tag:theconversation.com,2011:/ca-fr/topics/photons-2839/articlesPhotons – La Conversation2023-09-04T17:37:53Ztag:theconversation.com,2011:article/2124202023-09-04T17:37:53Z2023-09-04T17:37:53ZDogs don’t see life through rose-coloured glasses, nor in black and white<p>For a few months now, I’ve been treating six-year-old Samuel, who has the beginnings of myopia. He’s very quick for his age and often asks me questions about tests I give him, and about what I see inside his eyes. </p>
<p>But the last question surprised me. </p>
<p>Samuel knows that some people, like his father, don’t see colours well. But what about his little poodle, Scotch, he asked?</p>
<p>I’m not a veterinarian and don’t want to intrude on their domain of expertise. However, as an optometrist, I can offer some insights that might help answer Samuel’s question. </p>
<h2>Cones and rods</h2>
<p>Ambient light is composed of <a href="https://www.britannica.com/science/photon">particles (photons)</a>, which line up in rays. Light rays travel and strike objects. Some rays are absorbed, while others are reflected, depending on the characteristics of their surfaces and the composition of their materials. The wavelengths of the reflected rays determine the colour of the object as it is perceived by the eye. </p>
<p>Like everything about human vision, colour perception is complex. The retina, the sensitive part that lines the back of the eye, has two types of photon receptors: cones and rods. The cones, in the centre of the retina (fovea), perceive bright light and are <a href="https://askabiologist.asu.edu/rods-and-cones">responsible for colour perception</a>.</p>
<p>There are three types of cones. Each type contains a specific photo-pigment called opsin, which defines its nature. The opsin is produced under the influence of specific genes. The shortest opsin (“Cone S” for <em>short</em>) reacts mainly to blue light (420 nm). The longer one (“Cone L”) is more sensitive to orange-red light (560 nm) and the one in between (“Cone M” for <em>middle</em>) <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">is activated in the presence of green (530 nm)</a>.</p>
<p>However, each cone reacts to each of the rays entering the eye. For example, a red ball will produce a weak response from the S cone (3/10), a slightly stronger response from the M cone (5/10) and a <a href="https://opentextbc.ca/biology/chapter/17-5-vision/">strong response from the L cone</a> (8/10). </p>
<p>The brain combines the signals emitted by each of these cones to form the colour it perceives. So, in the previous example, the perceived colour would be coded 3-5-8, corresponding to what we know as red. A pink colour might have the code 4-6-6, and blue, 8-6-3. Each combination of the 3-cone signals is unique, which allows us to appreciate different hues in all their variations. </p>
<p>That is, as long as the genetic code is intact. </p>
<p>The genes associated with colour vision can be mutated or defective, in which case the person will be partially or completely impaired. The best known of these anomalies is colour blindness (red-green deficiency or daltonism).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="perception of a plant according to a colour-blind person" src="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=331&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=331&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=331&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=415&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=415&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544341/original/file-20230823-249-j6j8jf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=415&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Colour blindness is associated with difficulty in perceiving red and green.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>And what about animals?</h2>
<p>Colour vision, in humans as in animals, <a href="https://www.discoverwildlife.com/animal-facts/animal-vision-how-do-animals-see/">has developed throughout evolution</a> and results from the needs of each species according to their environment, the prey they hunt and the threats they need to avoid.</p>
<p>For example, birds have a fourth opsin that allows them to see ultraviolet (UV) light. Humans cannot perceive this light because our crystalline (internal) lens <a href="https://www.nwf.org/Magazines/National-Wildlife/2012/AugSept/Animals/Bird-Vision">filters UV rays</a>. UV rays influence birds’ behavioural decisions, including foraging and <a href="https://www.sciencedirect.com/science/article/abs/pii/S0065345408601059#:%7E:text=Publisher%20%20Summary,light%2C%20depending%20on%20the%20species.">their choice of a mate</a>.</p>
<p>So the colour vision of birds is more complex, with the result that the pigeon, which can perceive a myriad of colours, wins the <a href="https://nuscimagazine.com/the-world-through-the-eyes-of-a-pigeon/#:%7E:text=Though%20this%20range%20of%20vision,is%20one%20of%20these%20animal">award for best color vision among all species</a>.</p>
<p>Insects also perceive UV light. This function is essential for them to spot pollen, although their colour vision is very poor. Their eyes are made up of multiple lenses (ommatidia) that perceive <a href="https://www.mpg.de/14337047/how-flies-see-the-world">more movement than colour</a>. That’s much more practical while in fast flight.</p>
<p>Most forest-dwelling mammals have only two opsins. That’s because they lost the one associated with orange-red over the course of evolution. This explains why, unlike humans, these animals don’t perceive the orange bibs of hunters. </p>
<p>Snakes, on the other hand, are more sensitive to red and infrared light, thanks to their infrared receptors. This is an advantage when it comes to spotting prey, as <a href="https://phys.org/news/2006-08-snakes-vision-enables-accurate-prey.html">they can distinguish their heat even at night</a>. </p>
<p>Unsurprisingly, it’s the monkey that’s closest to the human, with its three opsins. It is said to be trichromatic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="close-up of a black dog's eyes" src="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/544344/original/file-20230823-19-pd8rjz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Dogs only perceive yellow-green and violet-blue. Colours are perceived as paler, like pastels.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Back to Scotch</h2>
<p>The vision of dogs — such as our friend Scotch — is <a href="https://ophtalmoveterinaire.com/maladies_oculaires/vision-comment-voit-mon-chien/#:%7E:text=For%20r%C3%A9sumer%2C%20the%20vision%20of,for%20his%20life%20of%20dog.">quite different</a>. </p>
<p>Unlike humans, dogs’ eyes are located on the side of the skull. As a result, dogs have a wider field of vision (250 to 280 degrees), but less simultaneous vision. </p>
<p>So Scotch’s vision of movement is well developed throughout his visual field. But his central vision is actually six times weaker than ours. This is equivalent to the vision of a very myopic person not wearing glasses. Why? Because the dog’s retina contains no fovea, and therefore fewer cones. </p>
<p>But while dogs eyes have fewer cones, they have more rods. And as an added bonus, they have an extra layer of the retina, called the tapetum lucidum — or carpet. When combined, these ingredients mean dogs see better in dim light and at night. This layer receives light and reflects it back onto the retina for a second exposure. This explains why your dog’s eyes seem to glow at night.</p>
<p>When it comes to colours, dogs are dichromats. They perceive only yellow-green and violet-blue. Colours are perceived paler, like pastels. And some colours don’t contrast: that’s why a red ball on green grass will appear to them as pale yellow on a grey background, with little contrast.</p>
<p>So it’s possible, depending on the colour of the ball, that Scotch will not see it, and as a result, will gaze up at Samuel with a lost look. As for the infrared, he perceives heat through his nose, not through his eyes.</p>
<p>Cats are also dichromats. Their vision is therefore similar to that of dogs, but their colour palette is different — more oriented towards violet and green. Having no perception of red-green, they are essentially colour-blind. They are also very short-sighted. Their clear vision is limited to a few meters in front of them.</p>
<p>Throughout cats’ evolution, other senses came to compensate for this. Among other things, although they only perceive certain contrasts, they are <a href="https://www.wired.com/2013/10/cats-eye-view/">formidable at perceiving movement</a>. Mice move quickly! </p>
<p>Every species adapts to its environment, and humans are no exception. Who knows what our colour vision will be like 500 years from now, after we’ve been exposed to more and more electronic devices and artificial colours? </p>
<p>But that’s a question for Samuel to answer when he’s older.</p><img src="https://counter.theconversation.com/content/212420/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Langis Michaud ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>Your faithful companion sees the world differently than you do, but it’s a mistake to assume dogs only see black, white and shades of grey.Langis Michaud, Professeur Titulaire. École d'optométrie. Expertise en santé oculaire et usage des lentilles cornéennes spécialisées, Université de MontréalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2079742023-07-05T12:23:21Z2023-07-05T12:23:21ZHow splitting sound might lead to a new kind of quantum computer<p>When you turn on a lamp to brighten a room, you are experiencing light energy transmitted as photons, which are small, discrete quantum packets of energy. These photons must obey the sometimes strange laws of quantum mechanics, which, for instance, dictate that photons are indivisible, but at the same time, allow a photon <a href="https://www.cambridge.org/highereducation/books/introduction-to-quantum-mechanics/990799CA07A83FC5312402AF6860311E#overview">to be in two places at once</a>. </p>
<p>Similar to the photons that make up beams of light, indivisible quantum particles <a href="https://news.mit.edu/2010/explained-phonons-0706">called phonons</a> make up a beam of sound. These particles emerge from the collective motion of quadrillions of atoms, much as a “stadium wave” in a sports arena is due to the motion of thousands of individual fans. When you listen to a song, you’re hearing a stream of these very small quantum particles.</p>
<p>Originally conceived to <a href="https://www.wiley.com/en-us/Introduction+to+Solid+State+Physics%2C+8th+Edition-p-9780471415268">explain the heat capacities of solids</a>, phonons are predicted to obey the same rules of quantum mechanics as photons. The technology to generate and detect individual phonons has, however, lagged behind that for photons. </p>
<p>That technology is only now being developed, in part by <a href="https://clelandlab.uchicago.edu/">my research group</a> at the Pritzker School of Molecular Engineering at the University of Chicago. <a href="https://scholar.google.com/citations?user=uE04v0gAAAAJ&hl=en&oi=ao">We are exploring</a> the fundamental quantum properties of sound by splitting phonons in half and entangling them together.</p>
<p>My group’s fundamental research on phonons may one day allow researchers to build a new type of quantum computer, called a mechanical quantum computer.</p>
<h2>Splitting sound with ‘bad’ mirrors</h2>
<p>To explore the quantum properties of phonons, our team uses acoustic mirrors, which can direct beams of sound. Our latest experiments, published in <a href="https://doi.org/10.1126/science.adg8715">a recent issue of Science</a>, however, involve “bad” mirrors, called beam splitters, that reflect about half the sound sent toward them and let the other half through. Our team decided to explore what happens when we direct a phonon at a beam splitter. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A diagram showing a line representing a beam splitter, which a phonon hits. Two dashed lines on either side of the beam splitter line demarcate that the phonon is both reflected off the beam splitter and transmitted to the other side, in superposition." src="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534146/original/file-20230626-29-lr358i.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A beam splitter for phonons – the phonon enters a superposition state where it is both reflected and transmitted until it is detected.</span>
<span class="attribution"><span class="source">A.N. Cleland</span></span>
</figcaption>
</figure>
<p>As a phonon is indivisible; it cannot be split. Instead, after interacting with the beam splitter, the phonon ends up in what is called a “<a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">superposition state</a>.” In this state the phonon is, somewhat paradoxically, both reflected and transmitted, and you’re equally likely to detect the phonon in either state. If you intervene and detect the phonon, half the time you will measure that it was reflected and half the time that it was transmitted; in a sense, the state is <a href="https://doi.org/10.1119/1.3243279">selected at random</a> by the detector. Absent the detection process, the phonon will remain in the superposition state of being both transmitted and reflected. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UjaAxUO6-Uw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A brief Ted-Ed explainer on superposition, which happens when particles can exist in multiple places at once.</span></figcaption>
</figure>
<p>This superposition effect was observed many years ago with photons. Our results indicate that phonons have the same property. </p>
<h2>Entangled phonons</h2>
<p>After demonstrating that phonons can go into quantum superpositions just as photons do, my team asked <a href="https://doi.org/10.1126/science.adg8715">a more complex question</a>. We wanted to know what would happen if we sent two identical phonons into the beam splitter, one from each direction. </p>
<p>It turns out that each phonon will go into a similar superposition state of half-transmitted and half-reflected. But because of the physics of the beam splitter, if we time the phonons precisely, they will quantum-mechanically interfere with one another. What emerges is actually a superposition state of two phonons going one way and two phonons going the other – the two phonons are thus <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/entanglement">quantum-mechanically entangled</a>. </p>
<p>In quantum entanglement, each phonon is in a superposition of reflected and transmitted, but the two phonons are locked together. This means detecting one phonon as having been transmitted or reflected forces the other phonon to be in the same state.</p>
<p>So, if you detect, you’ll always detect two phonons, going one way or the other, never one phonon going each way. This same effect for light, the combination of superposition and interference of two photons, is called the <a href="https://doi.org/10.1103/PhysRevLett.59.2044">Hong-Ou-Mandel effect</a>, after the three physicists who first predicted and observed it in 1987. Now, my group has demonstrated this effect with sound. </p>
<h2>The future of quantum computing</h2>
<p>These results suggest that it may now be possible to build a mechanical quantum computer using phonons. There are continuing efforts to build <a href="https://news.mit.edu/2020/explained-quantum-engineering-1210">optical quantum computers</a> that require only the emission, detection and interference of single photons. These are in parallel with efforts to build electrical quantum computers, which through the use of large numbers of entangled particles promise an exponential speedup for certain problems, such as factoring large numbers or simulating quantum systems.</p>
<p>A quantum computer using phonons could be very compact and self-contained, built entirely on a chip similar to that of a laptop computer’s processor. Its small size could make it easier to implement and use, if researchers can further expand and improve phonon-based technologies.</p>
<p>My group’s <a href="https://doi.org/10.1126/science.adg8715">experiments with phonons</a> use qubits – the same technology that powers electronic quantum computers – which means that as the technology for phonons catches up, there’s the potential to integrate phonon-based computers with electronic quantum computers. Doing so could yield new, potentially unique computational abilities.</p><img src="https://counter.theconversation.com/content/207974/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew N. Cleland receives funding from various US federal funding agencies. He is a fellow of the American Physical Society (APS) and the American Association for the Advancement of Science. He is currently Past Chair of the Division of Quantum Information of the APS, and in 2023 held a Fulbright Distinguished Chair. He is a founder and a board member of Spectradyne LLC, a startup company based in Los Angeles that is commercializing electrical and optical detection of nanoparticles in fluids.</span></em></p>Scientists show they can create quantum superpositions of sound particles, pointing to the potential for mechanical quantum computers.Andrew N. Cleland, Professor of Molecular Engineering Innovation and Enterprise, University of Chicago Pritzker School of Molecular EngineeringLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2058202023-06-27T12:23:57Z2023-06-27T12:23:57ZThe digital future may rely on ultrafast optical electronics and computers<figure><img src="https://images.theconversation.com/files/532461/original/file-20230616-23761-r0m0kq.jpeg?ixlib=rb-1.1.0&rect=38%2C15%2C1683%2C1239&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The author's lab's ultrafast optical switch in action.</span> <span class="attribution"><span class="source">Mohammed Hassan, University of Arizona</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>If you’ve ever wished you had a faster phone, computer or internet connection, you’ve encountered the personal experience of hitting a limit of technology. But there might be help on the way.</p>
<p>Over the past several decades, scientists and engineers <a href="https://scholar.google.com/citations?user=JA0qsY0AAAAJ&hl=en&oi=ao">like me</a> have worked to develop faster transistors, the electronic components underlying modern electronic and digital communications technologies. These efforts have been based on a category of materials called semiconductors that have special electrical properties. <a href="https://doi.org/10.1038/483S43a">Silicon</a> is perhaps the best known example of this type of material. </p>
<p>But about a decade ago, scientific efforts hit the speed limit of semiconductor-based transistors. Researchers simply can’t make electrons move faster through these materials. One way engineers are trying to address the speed limits inherent in moving a current through silicon is to design shorter physical circuits – essentially giving electrons less distance to travel. Increasing the computing power of a chip comes down to increasing the number of transistors. However, even if researchers are able to get transistors to be very small, they won’t be fast enough for the faster processing and data transfer speeds people and businesses will need.</p>
<p>My <a href="https://hassan.lab.arizona.edu">research group’s work</a> aims to develop faster ways to move data, using ultrafast laser pulses in free space and optical fiber. The laser light travels through optical fiber with almost no loss and with a very low level of noise.</p>
<p>In our most recent study, published in February 2023 in Science Advances, we took a step toward that, demonstrating that it’s possible to use <a href="https://doi.org/10.1126/sciadv.adf1015">laser-based systems</a> equipped with optical transistors, which depend on photons rather than voltage to move electrons, and to transfer information much more quickly than current systems – and do so more effectively than <a href="https://doi.org/10.1038/s41586-021-03866-9">previously reported optical switches</a>.</p>
<h2>Ultrafast optical transistors</h2>
<p>At their most fundamental level, digital transmissions involve a signal switching on and off to represent ones and zeros. Electronic transistors use voltage to send this signal: When the voltage induces the electrons to flow through the system, they signal a 1; when there are no electrons flowing, that signals a 0. This requires a source to emit the electrons and a receiver to detect them. </p>
<p>Our system of ultrafast optical data transmission is based on light rather than voltage. Our research group is one of many working with optical communication at the transistor level – the building blocks of modern processors – to get around the current limitations with silicon. </p>
<p>Our system controls reflected light to transmit information. When light shines on a piece of glass, most of it passes through, though a little bit might reflect. That is what you experience as glare when driving toward sunlight or looking through a window.</p>
<p>We use two laser beams transmitted from two sources passing through the same piece of glass. One beam is constant, but its transmission through the glass is controlled by the second beam. By using the second beam to shift the properties of the glass from transparent to reflective, we can start and stop the transmission of the constant beam, switching the optical signal from on to off and back again very quickly. </p>
<p>With this method, we can switch the glass properties much more quickly than current systems can send electrons. So we can send many more on and off signals – zeros and ones – in less time.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a hand holds a bundle of optical fibers between thumb and first finger" src="https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=441&fit=crop&dpr=1 600w, https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=441&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=441&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=554&fit=crop&dpr=1 754w, https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=554&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/534180/original/file-20230626-1803-19w9pt.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=554&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The author’s research group has developed a way to switch light beams on and off, like those passing through these optical fibers, 1 million billion times a second.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/bundle-of-light-wave-cables-fibre-optic-news-photo/976186008">Mediacolors/Construction Photography/Avalon via Getty Images</a></span>
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<h2>How fast are we talking?</h2>
<p>Our study took the first step to transmitting data 1 million times faster than if we had used the typical electronics. With electrons, the maximum speed for transmitting data is a <a href="https://www.wolframalpha.com/input?i=nanosecond">nanosecond</a>, one-billionth of a second, which is very fast. But the optical switch we constructed was able to transmit data a million times faster, which took just a few hundred <a href="https://www.wolframalpha.com/input?i=attosecond">attoseconds</a>.</p>
<p>We were also able to transmit those signals securely so that an attacker who tried to intercept or modify the messages would fail or be detected. </p>
<p>Using a laser beam to carry a signal, and adjusting its signal intensity with glass controlled by another laser beam, means the information can travel not only more quickly but also much greater distances. </p>
<p>For instance, the James Webb Space Telescope recently transmitted <a href="https://theconversation.com/james-webb-space-telescope-an-astronomer-explains-the-stunning-newly-released-first-images-186800">stunning images from far out in space</a>. These pictures were transferred as data from the telescope to the base station on Earth at a rate of one “on” or “off” <a href="https://webbtelescope.org/quick-facts">every 35 nanosconds</a> using optical communications.</p>
<p>A laser system like the one we’re developing could speed up the transfer rate a billionfold, allowing faster and clearer exploration of deep space, more quickly revealing the universe’s secrets. And someday computers themselves might run on light.</p><img src="https://counter.theconversation.com/content/205820/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mohammed Hassan receives funding from the Gordon and Betty Moore Foundation and the Air Force Office of Scientific Research.</span></em></p>A researcher explains developments in using light rather than electrons to transmit information securely and quickly, even over long distances.Mohammed Hassan, Associate Professor of Physics and Optical Sciences, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1919292022-10-07T13:34:23Z2022-10-07T13:34:23ZNobel-winning quantum weirdness undergirds an emerging high-tech industry, promising better ways of encrypting communications and imaging your body<figure><img src="https://images.theconversation.com/files/488631/original/file-20221006-14-mzyckh.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C3000%2C2384&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Devices like this experimental apparatus can produce pairs of photons that are linked, or 'entangled'.</span> <span class="attribution"><a class="source" href="https://www.ornl.gov/news/researchers-reach-quantum-networking-milestone-real-world-environment">Carlos Jones/ORNL, U.S. Dept. of Energy</a></span></figcaption></figure><p>Unhackable communications devices, high-precision GPS and high-resolution medical imaging all have something in common. These technologies – some under development and some already on the market all rely on the non-intuitive quantum phenomenon of <a href="https://theconversation.com/what-is-quantum-entanglement-a-physicist-explains-the-science-of-einsteins-spooky-action-at-a-distance-191927">entanglement</a>.</p>
<p>Two quantum particles, like pairs of atoms or photons, can become entangled. That means a property of one particle is linked to a property of the other, and a change to one particle instantly affects the other particle, regardless of how far apart they are. This correlation is a key resource in quantum information technologies. </p>
<p>For the most part, quantum entanglement is still a subject of physics research, but it’s also a component of commercially available technologies, and it plays a starring role in the emerging <a href="https://www.google.com/search?hl=en&as_q=list+of+quantum+information+processing+market+research+reports&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&as_filetype=&tbs=">quantum information processing industry</a>.</p>
<h2>Pioneers</h2>
<p>The <a href="https://theconversation.com/nobel-prize-physicists-share-prize-for-insights-into-the-spooky-world-of-quantum-mechanics-191884">2022 Nobel Prize in Physics</a> recognized the profound legacy of <a href="https://www.nobelprize.org/prizes/physics/2022/aspect/facts/">Alain Aspect</a> of France, <a href="https://www.nobelprize.org/prizes/physics/2022/clauser/facts/">John F. Clauser</a> of the U.S. and Austrian <a href="https://www.nobelprize.org/prizes/physics/2022/zeilinger/facts/">Anton Zeilinger</a>’s experimental work with quantum entanglement, which has personally touched me since the start of my graduate school career as <a href="https://scholar.google.com/citations?hl=en&user=WTPrTLUAAAAJ&view_op=list_works&sortby=pubdate">a physicist</a>. Anton Zeilinger was a mentor of my Ph.D. mentor, <a href="https://physics.illinois.edu/people/directory/profile/kwiat">Paul Kwiat</a>, which heavily influenced my dissertation on experimentally understanding decoherence in photonic entanglement. </p>
<p><a href="https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448/">Decoherence</a> occurs when the environment interacts with a quantum object – in this case a photon – to knock it out of the quantum state of superposition. In <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">superposition</a>, a quantum object is isolated from the environment and exists in a strange blend of two opposite states at the same time, like a coin toss landing as both heads and tails. Superposition is necessary for two or more quantum objects to become entangled.</p>
<h2>Entanglement goes the distance</h2>
<p>Quantum entanglement is a critical element of quantum information processing, and photonic entanglement of the type pioneered by the Nobel laureates is crucial for transmitting quantum information. Quantum entanglement can be used to build large-scale quantum communications networks.</p>
<p>On a path toward long-distance quantum networks, Jian-Wei Pan, one of Zeilinger’s former students, and colleagues demonstrated entanglement distribution to two locations separated by 764 miles (1,203 km) on Earth <a href="https://doi.org/10.1126/science.aan3211">via satellite transmission</a>. However, direct transmission rates of quantum information are limited due to <a href="https://doi.org/10.1038/ncomms15043">loss</a>, meaning too many photons get absorbed by matter in transit so not enough reach the destination. </p>
<p>Entanglement is critical for solving this roadblock, through the nascent technology of quantum repeaters. An important milestone for early quantum repeaters, called entanglement swapping, <a href="https://link.aps.org/doi/10.1103/PhysRevLett.80.3891">was demonstrated</a> by Zeilinger and colleagues in 1998. Entanglement swapping links one each of two pairs of entangled photons, thereby entangling the two initially independent photons, which can be far apart from each other.</p>
<h2>Quantum protection</h2>
<p>Perhaps the most well known quantum communications application is Quantum Key Distribution (QKD), which allows someone to securely distribute encryption keys. If those keys are stored properly, they will be secure, even from future powerful, code-breaking quantum computers. </p>
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<figcaption><span class="caption">How quantum encryption keeps secrets safe.</span></figcaption>
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<p>While the first proposal for QKD did not explicitly require entanglement, an entanglement-based version was subsequently <a href="https://link.aps.org/doi/10.1103/PhysRevLett.67.661">proposed</a>. Shortly after this proposal came the first demonstration of the technique, through the air over a short distance on a <a href="https://doi.org/10.1007/BF00191318">table-top</a>. The first demonstrations of entangement-based QKD were published by research groups led by <a href="https://doi.org/10.1103/PhysRevLett.84.4729">Zeilinger</a>, <a href="https://doi.org/10.1103/PhysRevLett.84.4737">Kwiat</a> and <a href="https://doi.org/10.1103/PhysRevLett.84.4733">Nicolas Gisin</a> were published in the same issue of Physical Review Letters in May 2000.</p>
<p>These entanglement-based distributed keys can be used to dramatically improve the security of communications. A first important demonstration along these lines was from the Zeilinger group, which conducted a <a href="https://doi.org/10.1364/OPEX.12.003865">bank wire transfer in Vienna, Austria, in 2004</a>. In this case, the two halves of the QKD system were located at the headquarters of a large bank and the Vienna City Hall. The optical fibers that carried the photons were installed in the Vienna sewer system and spanned nine-tenths of a mile (1.45 km).</p>
<h2>Entanglement for sale</h2>
<p>Today, there are a handful of companies that have commercialized quantum key distribution technology, including my group’s collaborator <a href="https://qubitekk.com/">Qubitekk</a>, which focuses on an entanglement-based approach to QKD. With a more recent commercial Qubitekk system, my colleagues and I demonstrated <a href="https://doi.org/10.1038/s41598-022-16090-w">secure smart grid communications</a> in Chattanooga, Tennessee.</p>
<p>Quantum communications, computing and sensing technologies are of <a href="https://idstch.com/technology/photonics/entangled-photon-sources-is-critical-technology-for-secure-communications-systems/">great interest to the military and intelligence communities</a>. Quantum entanglement also promises to boost medical imaging through <a href="https://doi.org/10.1038/srep37714">optical sensing</a> and high-resolution <a href="https://news.engineering.arizona.edu/news/quantum-entanglement-offers-unprecedented-precision-gps-imaging-and-beyond">radio frequency detection</a>, which could also improve GPS positioning. There’s even a company gearing up to <a href="https://www.techrepublic.com/article/quantum-entanglement-as-a-service-the-key-technology-for-unbreakable-networks/">offer entanglement-as-a-service</a> by providing customers with network access to entangled qubits for secure communications.</p>
<p>There are many other quantum applications that have been proposed and have yet to be invented that will be enabled by future entangled quantum networks. Quantum computers will perhaps have the most direct impact on society by enabling direct simulation of problems that do not scale well on conventional digital computers. In general, quantum computers produce complex entangled networks when they are operating. These computers could have huge impacts on society, ranging from reducing energy consumption to developing personally tailored medicine. </p>
<p>Finally, entangled quantum sensor networks promise the capability to measure theorized phenomena, such as dark matter, that cannot be seen with today’s conventional technology. The strangeness of quantum mechanics, elucidated through decades of fundamental experimental and theoretical work, has given rise to a new burgeoning global quantum industry.</p><img src="https://counter.theconversation.com/content/191929/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas Peters receives funding from The United States Department of Energy (DOE) Office of Science Advanced Scientific Computing Research program and DOE's Office of Cybersecurity, Energy Security and Emergency Response. He is affiliated with Oak Ridge National Laboratory. </span></em></p>Quantum entanglement is the stuff of sci-fi, advanced physics research and, increasingly, technology used by governments, banks and the military.Nicholas Peters, Joint Faculty, University of TennesseeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1716082021-12-07T14:58:31Z2021-12-07T14:58:31ZQuantum entanglement: what it is, and why physicists want to harness it<figure><img src="https://images.theconversation.com/files/434373/original/file-20211129-25-djd15g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Two particles are said to be entangled when one cannot be perfectly described without information about the other being included.</span> <span class="attribution"><span class="source">Shutterstock/ezphoto</span></span></figcaption></figure><p>“Quantum entanglement” is one of several plot devices that crops up in modern sci-fi movies. Fans of the <a href="https://www.wired.co.uk/article/marvel-movies-science">Marvel superhero movies</a>, for instance, will be familiar with the idea of different time lines merging and intersecting, or characters’ destinies becoming intertwined through seemingly magical means.</p>
<p>But “quantum entanglement” isn’t just a sci-fi buzzword. It’s a very real, perplexing and useful phenomenon. “Entanglement” is one aspect of the broader collection of ideas in physics known as quantum mechanics, which is a theory that describes the behaviour of nature at the atomic, and even subatomic, level.</p>
<p>Understanding and harnessing entanglement is key to creating many cutting-edge technologies. These include quantum computers, which can solve certain problems far faster than ordinary computers, and quantum communication devices, which would allow us to communicate with one another without the slightest possibility of a eavesdropper listening in.</p>
<p>But what exactly <em>is</em> quantum entanglement? Two particles in quantum mechanics are said to be <em>entangled</em> when one of the particles cannot be perfectly described without including all of the information about the other one: the particles are “connected” in such a way that they are not independent of one another. While this sort of idea may seem to make sense at first glance, it is a difficult concept to grasp – and physicists are still learning more about it.</p>
<h2>Quantum dice</h2>
<p>Suppose that I give you and your friend, Thandi, each a small, opaque black box. Each box contains an ordinary six-sided die. You are both told to lightly shake your boxes to jumble the dice around. Then you part ways. Thandi goes home to one South African city, Cape Town; you return to another, Durban. You don’t communicate with each other during the process. When you get home, you each open your box and look at the upward-facing number on your die. </p>
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<img alt="" src="https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434372/original/file-20211129-21-q1lxam.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><span class="source">Shutterstock</span></span>
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<p>Ordinarily, there would be no correlation between the numbers you and Thandi see. She would be equally likely to observe any number between 1 and 6, as would you; importantly, the number she sees on her die would have no bearing whatsoever on the number you see on yours. </p>
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Read more:
<a href="https://theconversation.com/is-reality-a-game-of-quantum-mirrors-a-new-theory-suggests-it-might-be-162936">Is reality a game of quantum mirrors? A new theory suggests it might be</a>
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<p>This is unsurprising – indeed, it’s how the world normally works. However, if we could make this example “quantum”, it could behave quite differently. Suppose that I now tell Thandi and you to first lightly tap your boxes together, before then separately shaking them and heading your separate ways. </p>
<p>In a quantum mechanics analogy, this action of tapping the boxes against one another would enchant the dice and link – or entangle – them in a mysterious fashion: once you each arrive home, open your boxes and look at the numbers, your number and Thandi’s are guaranteed to be perfectly correlated. If you see a ‘4’ in Durban, you know that Thandi in Cape Town is guaranteed to measure a ‘4’ on her die too; if you happen to see a ‘6’, so will she.</p>
<p>In this analogy, the dice represent individual particles (like atoms or particles of light called photons) and the magic act of tapping the boxes together physically is what entangles them, so that measuring one die gives us information about the other.</p>
<h2>Making better entanglement</h2>
<p>As far as we know, there’s no magical box-tapping action to enchant a pair of dice or other objects on our human, macroscopic scale (if there were, we would be able to experience quantum mechanics in our everyday life and it would probably not be such a foreign, perplexing concept). For now, scientists have to be content with using things on the microscopic level, where it is much easier to observe quantum effects, like charged atoms called ions or special superconducting devices called <a href="https://www.youtube.com/watch?v=9MFPvrjHgF0">transmons</a>.</p>
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<a href="https://theconversation.com/explainer-what-is-quantum-machine-learning-and-how-can-it-help-us-114627">Explainer: what is quantum machine learning and how can it help us?</a>
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<p>This is the kind of work carried out in the University of the Witwatersrand’s <a href="https://structured-light.org/">Structured Light Laboratory</a>, in South Africa. Instead of ions or transmons, however, researchers in the lab use particles of light, called photons, to better understand quantum mechanics and its implications. We are interested in using the quantum nature of light for a variety of purposes: from designing efficient communication systems which are completely unhackable by a malevolent third party, to creating methods of imaging sensitive biological samples without damaging them. </p>
<p>Studies like this often require us to start with specially created states of entangled photons. But it’s not as simple as putting two dice in separate boxes and tapping them together. The processes used to create entangled photons in a real laboratory are constrained by many experimental variables. These include the shape of laser beams used in experiments and the sizes of small crystals where the entangled photons are created. These can give subpar outputs – or unideal states – that require researchers to selectively throw away some measurements once an experiment is done. This is not an optimal situation: photons are discarded and so energy is wasted.</p>
<p>A group of researchers from the lab, myself among them, recently took a step towards solving this problem. In <a href="https://onlinelibrary.wiley.com/doi/10.1002/qute.202100066">a journal article</a>, we mathematically calculated what the optimal laser shape needs to be in order to, as best as possible, create the entangled state that an experimenter would want to start their experiment with. The method proposes changing the input laser beam shape at the beginning of an experiment to maximise the entangled photon creation process later in the experiment. This will mean more photons available to perform your experiment the way you want to, and fewer stray ones.</p>
<p>Improving the efficiency of the entanglement creation and manipulation process, using techniques such as the one proposed, will be important to optimise the efficiency of a number of other quantum technologies, like quantum cryptography systems and the other technologies already mentioned. This is especially important as the fourth industrial revolution moves ahead globally and technologies with quantum mechanics at their cores undoubtedly <a href="https://www.weforum.org/agenda/2019/10/quantum-computers-next-frontier-classical-google-ibm-nasa-supremacy">become more commonplace</a>.</p><img src="https://counter.theconversation.com/content/171608/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas Bornman receives funding from the CSIR Scarce Skills Programme.</span></em></p>The quantum nature of light can be harnessed for a variety of purposes.Nicholas Bornman, Ph.D. student, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1551252021-02-15T18:51:20Z2021-02-15T18:51:20ZA tiny crystal device could boost gravitational wave detectors to reveal the birth cries of black holes<figure><img src="https://images.theconversation.com/files/384196/original/file-20210215-15-u84vo1.jpg?ixlib=rb-1.1.0&rect=8%2C13%2C2986%2C2645&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NSF / LIGO / Sonoma State University / A Simonnet</span>, <span class="license">Author provided</span></span></figcaption></figure><p>In 2017, astronomers witnessed the birth of a black hole for the first time. Gravitational wave detectors picked up the ripples in spacetime caused by <a href="https://en.wikipedia.org/wiki/GW170817">two neutron stars colliding</a> to form the black hole, and other telescopes then observed the resulting explosion.</p>
<p>But the real nitty-gritty of how the black hole formed, the movements of matter in the instants before it was sealed away inside the black hole’s event horizon, went unobserved. That’s because the gravitational waves thrown off in these final moments had such a high frequency that our current detectors can’t pick them up.</p>
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Read more:
<a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">At last, we've found gravitational waves from a collapsing pair of neutron stars</a>
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<p>If you could observe ordinary matter as it turns into a black hole, you would be seeing something similar to the Big Bang played backwards. The scientists who design gravitational wave detectors have been hard at work to figure out how improve our detectors to make it possible.</p>
<p>Today our team is publishing <a href="https://www.nature.com/articles/s42005-021-00526-2">a paper</a> that shows how this can be done. Our proposal could make detectors 40 times more sensitive to the high frequencies we need, allowing astronomers to listen to matter as it forms a black hole.</p>
<p>It involves creating weird new packets of energy (or “quanta”) that are a mix of two types of quantum vibrations. Devices based on this technology could be added to existing gravitational wave detectors to gain the extra sensitivity needed.</p>
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<img alt="" src="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383921/original/file-20210211-17-q8esrc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=464&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">An artist’s conception of photons interacting with a millimetre scale phononic crystal device placed in the output stage of a gravitational wave detector.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
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<h2>Quantum problems</h2>
<p>Gravitational wave detectors such as the <a href="https://en.wikipedia.org/wiki/LIGO">Laser Interferometer Gravitational-wave Observatory (LIGO)</a> in the United States use lasers to measure incredibly small changes in the distance between two mirrors. Because they measure changes 1,000 times smaller than the size of a single proton, the effects of quantum mechanics – the physics of individual particles or quanta of energy – play an important role in the way these detectors work.</p>
<p>Two different kinds of quantum packets of energy are involved, both predicted by Albert Einstein. In 1905 he predicted that light comes in packets of energy that we call <em>photons</em>; two years later, he predicted that heat and sound energy come in packets of energy called <em>phonons</em>. </p>
<p>Photons are used widely in modern technology, but phonons are much trickier to harness. Individual phonons are usually swamped by vast numbers of random phonons that are the heat of their surroundings. In gravitational wave detectors, phonons bounce around inside the detector’s mirrors, degrading their sensitivity.</p>
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<strong>
Read more:
<a href="https://theconversation.com/australias-part-in-the-global-effort-to-discover-gravitational-waves-54525">Australia's part in the global effort to discover gravitational waves</a>
</strong>
</em>
</p>
<hr>
<p>Five years ago physicists realised you could <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.211104">solve the problem</a> of insufficient sensitivity at high frequency with devices that <em>combine</em> phonons with photons. They showed that devices in which energy is carried in quantum packets that share the properties of both phonons and photons can have quite remarkable properties. </p>
<p>These devices would involve a radical change to a familiar concept called “resonant amplification”. Resonant amplification is what you do when you push a playground swing: if you push at the right time, all your small pushes create big swinging.</p>
<p>The new device, called a “white light cavity”, would amplify all frequencies equally. This is like a swing that you could push any old time and still end up with big results.</p>
<p>However, nobody has yet worked out how to make one of these devices, because the phonons inside it would be overwhelmed by random vibrations caused by heat.</p>
<h2>Quantum solutions</h2>
<p>In <a href="https://www.nature.com/articles/s42005-021-00526-2">our paper</a>, published in Communications Physics, we show how two different projects currently under way could do the job.</p>
<p>The Niels Bohr Institute in Copenhagen has been <a href="https://www.nature.com/articles/nnano.2017.101">developing devices</a> called phononic crystals, in which thermal vibrations are controlled by a crystal-like structure cut into a thin membrane. The Australian Centre of Excellence for Engineered Quantum Systems has also demonstrated <a href="https://www.nature.com/articles/srep02132">an alternative system</a> in which phonons are trapped inside an ultrapure quartz lens.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=415&fit=crop&dpr=1 600w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=415&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=415&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=521&fit=crop&dpr=1 754w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=521&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/383913/original/file-20210211-16-1girq3t.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=521&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artist’s impression of a tiny device that could boost gravitational wave detector sensitivity in high frequencies.</span>
<span class="attribution"><span class="source">Carl Knox / OzGrav / Swinburne University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We show both of these systems satisfy the requirements for creating the “negative dispersion” – which spreads light frequencies in a reverse rainbow pattern – needed for white light cavities. </p>
<p>Both systems, when added to the back end of existing gravitational wave detectors, would improve the sensitivity at frequencies of a few kilohertz by the 40 times or more needed for listening to the birth of a black hole.</p>
<h2>What’s next?</h2>
<p>Our research does not represent an instant solution to improving gravitational wave detectors. There are enormous experimental challenges in making such devices into practical tools. But it does offer a route to the 40-fold improvement of gravitational wave detectors needed for observing black hole births.</p>
<p>Astrophysicists have predicted <a href="https://journals.aps.org/prd/abstract/10.1103/PhysRevD.100.043005">complex gravitational waveforms</a> created by the convulsions of neutron stars as they form black holes. These gravitational waves could allow us to listen in to the nuclear physics of a collapsing neutron star. </p>
<p>For example, it has been shown that they can clearly reveal whether the neutrons in the star remain as neutrons or whether they <a href="https://en.wikipedia.org/wiki/Quark_star">break up into a sea of quarks</a>, the tiniest subatomic particles of all. If we could observe neutrons turning into quarks and then disappearing into the black hole singularity, it would be the exact reverse of the Big Bang where out of the singularity, the particles emerged which went on to create our universe.</p><img src="https://counter.theconversation.com/content/155125/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. </span></em></p>A small add-on to existing gravitational wave detectors could reveal what happens to matter as it becomes a black hole, a process like the big bang in reverse.David Blair, Emeritus Professor, ARC Centre of Excellence for Gravitational Wave Discovery, OzGrav, The University of Western AustraliaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1328272020-06-22T12:16:50Z2020-06-22T12:16:50ZWhat is the slowest thing on Earth?<figure><img src="https://images.theconversation.com/files/342474/original/file-20200617-94049-47hnes.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Lasers create colorful light shows at concerts, are used by doctors in surgeries – and are used in scientific laboratories.</span> <span class="attribution"><span class="source">EyeWolf/Getty Images</span></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What is the slowest thing on Earth? – Jiwon, Brookline, Massachusetts</strong></p>
</blockquote>
<hr>
<p>In the words of the infamous villain, <a href="https://www.imdb.com/title/tt0118655/">Dr. Evil</a>: “Lasers.” </p>
<p>Lasers focus a narrow, directed beam of light on a specific spot, making them a great tool for cutting, burning, welding – or in the case of Dr. Evil, shooting enemies from atop a shark. These activities all produce or require heat. Laser beams travel at the speed of light, more than 670 million miles per hour, making them the fastest thing in the universe.</p>
<p>So how does a laser produce the slowest thing on Earth? </p>
<p>First, it’s important to understand the relationship between an object’s temperature and its speed. The hotter something is, the more energy it has and the faster it moves. Even things that appear to be perfectly still – say, a pen or your notebook – are not. On a microscopic level, the particles they’re made of are moving rapidly. This is even true of living beings.</p>
<p>Let’s use the sloth as an example. If you zoom in on the molecules that make up this famously slow animal’s body, you’ll see them behaving like kids jumping around inside a bounce house. Why? About <a href="https://doi.org/10.2307/1379840">70% of this creature’s body is made up of water</a> and those water molecules are bouncing around at <a href="https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Map%3A_Physical_Chemistry_(McQuarrie_and_Simon)/18%3A_Partition_Functions_and_Ideal_Gases/18.11%3A_The_Equipartition_Principle">hundreds of miles per hour</a>.</p>
<h2>Laser cooling</h2>
<p>So it might seem surprising that I use bright, intense lasers to cool things down in my lab experiments. <a href="https://scholar.google.com/citations?user=rm6lxY0AAAAJ&hl=en&oi=sra">I am a physicist</a> who is interested in how atoms and molecules behave at the very coldest temperatures. It’s a strange world where quantum mechanics rules. In this realm, particles sometimes behave like waves in the ocean, and believe it or not, can sometimes be in two different places at the same time. </p>
<p>To study this extraordinary behavior, I use lasers to produce clouds of frigid atoms that are the coldest things on Earth – which we call <a href="https://www.britannica.com/science/Bose-Einstein-condensate">Bose-Einstein condensates</a>. When you cool a bunch of atoms down to almost absolute zero, the coldest possible temperature, atoms start to obey quantum mechanics and behave in surprising ways. </p>
<p>Studying ultra-cold atom clouds might provide clues about how other weird materials, <a href="https://theconversation.com/physicists-hunt-for-room-temperature-superconductors-that-could-revolutionize-the-worlds-energy-system-80707">like superconductors</a>, work. Superconductors carry electricity much better than existing materials, so well that they may someday be used to build super high-speed trains.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/340717/original/file-20200609-21208-18v2oum.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">In 1995, researchers cooled atoms lower than ever before and created a new state of matter that had been predicted by Albert Einstein. This graphic shows snapshots as the atoms condensed from more spread-out red, yellow and green areas into very dense blue and white areas.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Quantum_Physics;_Bose_Einstein_condensate_(5940505475).jpg#/media/File:Quantum_Physics;_Bose_Einstein_condensate_(5940505475).jpg">NIST/JILA/CU-Boulder</a></span>
</figcaption>
</figure>
<h2>Creating the slowest thing on Earth</h2>
<p>So how exactly do lasers chill out a cloud of atoms? In the lab, we start by shining lasers at atoms of a silvery-white metal called ytterbium. These atoms, which are really hot, are held inside a 1-foot-wide chamber. But after a few seconds under the laser beam, they cool off, slow down and become trapped together in the center of the chamber. </p>
<p>How does this happen? All light, including a laser, is made up of photons, which are packets of energy that are constantly moving. When we shine a laser into our chamber, the atoms collide with streams of photons in the beam and slow down and get colder – like what would happen if you tried running really fast against a strong wind.</p>
<p>These little collisions bring the temperature of the atom cloud down to just a few millionths of a degree above absolute zero. That’s 459 degrees below 0 degrees Fahrenheit.</p>
<p>But that’s still not enough to give this cloud the prize for being the slowest thing on Earth. It takes one last step to make it just a little colder, a technique we physicists call “<a href="https://www.sciencedirect.com/science/article/pii/S1049250X08601019">evaporative cooling</a>.” </p>
<p>First, we capture all the atoms, sometimes using a magnetic field made by running electricity through a wound-up wire. This creates an invisible well that holds the atoms: Picture marbles sitting at the bottom of a bowl. Then we lower the sides of this bowl-shaped force field by decreasing the electric current that runs through the wire. That allows the faster, warmer atoms to zoom out of the “bowl” and escape the trap. </p>
<p>Only the slower atoms are left behind – and they are truly beyond freezing: one-tenth of one-millionth of a degree above absolute zero. The atoms in this cloud move in slow motion: If they traveled in a straight line instead of bouncing around, it would take them an entire hour to travel across a room. For comparison, the molecules in your body could dash across that room in just a fraction of a second.</p>
<p>The atoms in our frigid atom cloud quite literally move at less than a snail’s pace – and that cloud is the slowest thing on Earth.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/132827/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Katie McCormick does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Physicists can use bright, hot lasers to slow atoms down so much that they measure -459 degrees Fahrenheit.Katie McCormick, Postdoctoral Scholar of Physics, University of WashingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1001552018-08-28T21:06:19Z2018-08-28T21:06:19ZNew era of astronomy uncovers clues about the cosmos<figure><img src="https://images.theconversation.com/files/231953/original/file-20180814-2894-1tzyen8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An illustration of two neutron stars spinning around each other while merging.</span> <span class="attribution"><span class="source"> NASA/CXC/Trinity University/D. Pooley et al.</span></span></figcaption></figure><p>Astronomers have had a blockbuster year. </p>
<p>In addition to tracking down <a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">a cosmic source of neutrinos</a>, they have detected the merger of <a href="https://theconversation.com/at-last-weve-found-gravitational-waves-from-a-collapsing-pair-of-neutron-stars-85528">two city-sized neutron stars, each more massive than the sun</a>. </p>
<p>The <a href="https://www.ligo.org/science/Publication-GW170817MMA/">discoveries were heralded</a> as evidence that a “<a href="https://www.ligo.org/science/Publication-GW170817MMA/">new era of multimessenger astronomy</a>” had arrived. </p>
<p>But what is multimessenger astronomy? </p>
<p>In our daily lives, we interpret the world around us based on different signals, such as sound waves, light (a type of electromagnetic wave) and skin pressure. Each of these signals may be carried by a different “messenger.” New messengers lead to new insights. So astronomers have eagerly welcomed a new set of messengers to their science.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230974/original/file-20180807-191044-7ega78.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Twenty-seven radio antennas make up the Karl G. Very Large Array in New Mexico. The VLA is an important tool for studying cosmic radio waves.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Many messengers</h2>
<p>For most of the history of astronomy, scientists primarily studied signals transmitted by one messenger, electromagnetic radiation. These waves, which move through space and time, are described by their wavelengths or the amount of energy found in their particles, the photons.</p>
<p>Radio waves have photons with the lowest amount of energy and the longest wavelengths, followed by infrared and optical light at intermediate energies and wavelengths. X-rays and gamma-rays have the shortest wavelengths and the highest energy. </p>
<p>But scientists study others messengers too: </p>
<ul>
<li>Cosmic rays: charged atomic particles and nuclei travelling near the speed of light.</li>
<li>Neutrinos: uncharged particles that see most of the universe as transparent.</li>
<li>Gravitational waves: wrinkles in the very fabric of space and time.</li>
</ul>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/230992/original/file-20180807-160647-1ql3xqb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The four messengers of astronomy.</span>
<span class="attribution"><span class="source">Adapted from IceCube Collaboration</span></span>
</figcaption>
</figure>
<p>And while some fields in astronomy have explored these messengers for years, astronomers have only recently observed events from well beyond the Milky Way with more than one messenger at the same time. In just a few months, the number of sources where astronomers can piece together the signals from different messengers doubled.</p>
<h2>Like a walk on the beach</h2>
<p>Multimessenger astronomy is a natural evolution of astronomy. Scientists need more data to put together a complete picture of the objects they study and match the theories they develop with their observations. </p>
<p>Astronomers have combined different wavelengths of photons to piece together some of the mysteries of the universe. For example, the combination of radio and optical data played a major role in determining that the Milky Way is a spiral galaxy in 1951.</p>
<p>And astronomy continues to reveal great results about our universe using just one messenger, photons. So if multimessenger astronomy is just an evolutionary step of an incredible history of successes, does that mean it’s just a new buzzword?</p>
<p>We don’t think so.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=398&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=398&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228950/original/file-20180724-189313-s1tiw7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=398&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An artistic rendition of NASA’s Chandra X-ray Observatory. This space satellite produces the most detailed X-ray images of high energy astrophysical phenomena.</span>
<span class="attribution"><span class="source">NGST</span></span>
</figcaption>
</figure>
<p>Imagine you are walking along an ocean beach. You are enjoying the sight of an incredible sunset, hearing the rolling waves, feeling the sand beneath your feet and smelling the salty air. Your combined senses form a more complete experience. </p>
<p>With multimessenger astronomy, we hope to learn more from the universe by combining multiple messengers, just as we combine sight, hearing, touch and smell.</p>
<h2>But it’s not always a picnic</h2>
<p>The cultures of astronomers and particle physicists represent different approaches to science. In multimessenger astronomy, these cultures collide.</p>
<p>Astronomy is an observational field and not an experiment. We study astronomical objects that change over time (time-domain astronomy), which means we often have only one chance to observe a transient astronomical event.</p>
<p>Until recently, most time-domain astronomers worked in small teams, on many projects at once. We use resources like <a href="http://www.astronomerstelegram.org/">The Astronomer’s Telegram</a> or the <a href="https://gcn.gsfc.nasa.gov/">Gamma-ray Coordination Network</a> to rapidly communicate results, even before submitting scientific papers.</p>
<p>Since most of the expected sources of multimessenger signals are transient astronomical events, it’s a huge effort to capture the messengers besides photons.</p>
<hr>
<p>
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<strong>
Read more:
<a href="https://theconversation.com/the-icecube-observatory-detects-neutrino-and-discovers-a-blazar-as-its-source-99720">The IceCube observatory detects neutrino and discovers a blazar as its source</a>
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<p>Particle physicists have led the way in creating large international collaborations to tackle their hardest problems, including the <a href="https://home.cern/topics/large-hadron-collider">Large Hadron Collider</a>, the <a href="https://icecube.wisc.edu/">IceCube Neutrino Observatory</a> and the <a href="https://www.ligo.caltech.edu/">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a>. Corralling hundreds to thousands of researchers to work towards common goals requires comprehensive identification of roles, strict communication guidelines and many teleconferences.</p>
<p>The need to respond to rapid changes in a multimessenger source and the huge effort to capture multimessenger signals means astronomy and particle physics must merge towards one another to elicit the best of both cultures.</p>
<h2>The benefits of multimessenger astronomy</h2>
<p>While multimessenger astronomy is an evolution of what astronomers and particle physicists have done for decades, the combined results are intriguing.</p>
<p>The detection of gravitational waves from merging neutron stars confirmed that <a href="https://theconversation.com/cosmic-alchemy-colliding-neutron-stars-show-us-how-the-universe-creates-gold-86104">these collisions made a large fraction of the gold and platinum</a> on Earth (and throughout the universe). It also showed how these collisions give rise to (at least some) <a href="https://theconversation.com/how-we-discovered-gravitational-waves-from-neutron-stars-and-why-its-such-a-huge-deal-85647">short gamma-ray bursts</a> — the origin of these explosive events has been a huge open question in astronomy. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/228936/original/file-20180723-189310-18799bp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The IceCube Neutrino Observatory used a cubic kilometre of crystal-clear Antarctic ice to capture the signal of a rare neutrino that helped pinpoint a galaxy four billion light years away with a supermassive black hole launching a jet of photons and near light-speed particles directly at our Solar System.</span>
<span class="attribution"><span class="source">IceCube Collaboration/NSF</span></span>
</figcaption>
</figure>
<p>The first association of a neutrino with a single astronomical source provided a glimpse into how the universe makes its most energetic particles. Multimessenger astronomy is revealing details about some of the most extreme conditions in our universe.</p>
<p>The multimessenger perspective is already yielding more than the sum of its parts — and we can expect to see more surprising discoveries in the future. Elite teams across Canada are already contributing to the growth of this young field, and multimessenger astronomy promises to play a major role in our next decade of astronomical research in Canada — and across the world.</p><img src="https://counter.theconversation.com/content/100155/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Gregory Sivakoff receives funding from Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), and Alberta Economic Development and Trade (EDT). Gregory Sivakoff is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Gregory Sivakoff also serves on the Council of the American Association of Variable Star Observers (AAVSO), a non-profit citizen astronomy organization.
</span></em></p><p class="fine-print"><em><span>Daryl Haggard receives funding from the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholars Program, Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du Québec – Nature et technologies (FRQNT). Daryl Haggard is a member of several professional societies for astronomy and physics, including the Canadian Astronomical Society (CASCA), Canadian Association of Physicists (CAP), American Astronomical Society (AAS), and the AAS High Energy Astrophysics Division (HEAD). Daryl Haggard also serves on the Laser Interferometer Gravitational-Wave Observatory (LIGO) Program Advisory Committee.</span></em></p>Astronomers are now able to detect a host of signals streaming through the universe. This newfound ability is like gaining new senses and it’s opening the door to understanding the cosmos.Gregory Sivakoff, Associate Professor, University of AlbertaDaryl Haggard, Assistant Professor of Physics, McGill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/947002018-05-23T10:39:19Z2018-05-23T10:39:19ZThe Standard Model of particle physics: The absolutely amazing theory of almost everything<figure><img src="https://images.theconversation.com/files/219824/original/file-20180521-14978-36nv6i.jpg?ixlib=rb-1.1.0&rect=174%2C0%2C977%2C649&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">How does our world work on a subatomic level?</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Varsha_ys.jpg">Varsha Y S</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The Standard Model. What a dull name for the most accurate scientific theory known to human beings.</p>
<p>More than a quarter of the Nobel Prizes in physics of the last century are direct inputs to or direct results of the Standard Model. Yet its name suggests that if you can afford a few extra dollars a month you should buy the upgrade. <a href="https://scholar.google.com/citations?user=eQiX0m4AAAAJ&hl=en&oi=ao">As a theoretical physicist</a>, I’d prefer The Absolutely Amazing Theory of Almost Everything. That’s what the Standard Model really is.</p>
<p>Many recall the excitement among scientists and media over the 2012 <a href="https://home.cern/topics/higgs-boson">discovery of the Higgs boson</a>. But that much-ballyhooed event didn’t come out of the blue – it capped a five-decade undefeated streak for the Standard Model. Every fundamental force but gravity is included in it. Every attempt to overturn it to demonstrate in the laboratory that it must be substantially reworked – and there have been many over the past 50 years – has failed. </p>
<p>In short, the <a href="https://home.cern/about/physics/standard-model">Standard Model</a> answers this question: What is everything made of, and how does it hold together?</p>
<h2>The smallest building blocks</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219828/original/file-20180521-14991-vlfgkx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">But these elements can be broken down further.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Periodic_table_vectorial.png">Rubén Vera Koster</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>You know, of course, that the world around us is made of molecules, and molecules are made of atoms. Chemist <a href="https://www.famousscientists.org/dmitri-mendeleev/">Dmitri Mendeleev</a> figured out in the 1860s how to organize all atoms – that is, the elements – into the periodic table that you probably studied in middle school. But there are 118 different chemical elements. There’s antimony, arsenic, aluminum, selenium … and 114 more.</p>
<p>Physicists like things simple. We want to boil things down to their essence, a few basic building blocks. Over a hundred chemical elements is not simple. The ancients believed that everything is made of just five elements – <a href="https://en.wikipedia.org/wiki/Classical_element">earth, water, fire, air and aether</a>. Five is much simpler than 118. It’s also wrong. </p>
<p>By 1932, scientists knew that all those atoms are made of just three particles – neutrons, protons and electrons. The neutrons and protons are bound together tightly into the nucleus. The electrons, thousands of times lighter, whirl around the nucleus at speeds approaching that of light. Physicists <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html">Planck</a>, <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html">Bohr</a>, <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1933/schrodinger-bio.html">Schroedinger</a>, <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html">Heisenberg</a> and friends had invented a new science – <a href="https://en.wikipedia.org/wiki/Quantum_mechanics">quantum mechanics</a> – to explain this motion.</p>
<p>That would have been a satisfying place to stop. Just three particles. Three is even simpler than five. But held together how? The negatively charged electrons and positively charged protons are bound together by <a href="https://en.wikipedia.org/wiki/Electromagnetism">electromagnetism</a>. But the protons are all huddled together in the nucleus and their positive charges should be pushing them powerfully apart. The neutral neutrons can’t help. </p>
<p>What binds these protons and neutrons together? “Divine intervention” a man on a Toronto street corner told me; he had a pamphlet, I could read all about it. But this scenario seemed like a lot of trouble even for a divine being – keeping tabs on every single one of the universe’s 10⁸⁰ protons and neutrons and bending them to its will. </p>
<h2>Expanding the zoo of particles</h2>
<p>Meanwhile, nature cruelly declined to keep its zoo of particles to just three. Really four, because we should count the <a href="https://en.wikipedia.org/wiki/Photon">photon</a>, the particle of light that <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1921/einstein-bio.html">Einstein</a> described. Four grew to five when <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1936/anderson-bio.html">Anderson</a> measured electrons with positive charge – positrons – striking the Earth from outer space. At least <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-bio.html">Dirac</a> had predicted these first anti-matter particles. Five became six when the pion, which <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1949/yukawa-bio.html">Yukawa</a> predicted would hold the nucleus together, was found. </p>
<p>Then came the muon – 200 times heavier than the electron, but otherwise a twin. “Who ordered that?” <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1944/rabi-bio.html">I.I. Rabi</a> quipped. That sums it up. Number seven. Not only not simple, redundant.</p>
<p>By the 1960s there were hundreds of “fundamental” particles. In place of the well-organized periodic table, there were just long lists of baryons (heavy particles like protons and neutrons), mesons (like <a href="https://en.wikipedia.org/wiki/Hideki_Yukawa">Yukawa</a>’s pions) and leptons (light particles like the electron, and the elusive neutrinos) – with no organization and no guiding principles.</p>
<p>Into this breach sidled the Standard Model. It was not an overnight flash of brilliance. No Archimedes leapt out of a bathtub shouting “eureka.” Instead, there was a series of crucial insights by a few key individuals in the mid-1960s that transformed this quagmire into a simple theory, and then five decades of experimental verification and theoretical elaboration. </p>
<p><a href="https://home.cern/about/updates/2014/01/fifty-years-quarks">Quarks</a>. They come in six varieties we call flavors. Like ice cream, except not as tasty. Instead of vanilla, chocolate and so on, we have up, down, strange, charm, bottom and top. In 1964, <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1969/gell-mann-bio.html">Gell-Mann</a> and <a href="https://www.macfound.org/fellows/113/">Zweig</a> taught us the recipes: Mix and match any three quarks to get a baryon. Protons are two ups and a down quark bound together; neutrons are two downs and an up. Choose one quark and one antiquark to get a meson. A pion is an up or a down quark bound to an anti-up or an anti-down. All the material of our daily lives is made of just up and down quarks and anti-quarks and electrons.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=536&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=536&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=536&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=673&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=673&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219958/original/file-20180522-51127-4tx5tr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=673&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Standard Model of elementary particles provides an ingredients list for everything around us.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Standard_Model_From_Fermi_Lab.jpg">Fermi National Accelerator Laboratory</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Simple. Well, simple-ish, because keeping those quarks bound is a feat. They are tied to one another so tightly that you never ever find a quark or anti-quark on its own. The theory of that binding, and the particles called gluons (chuckle) that are responsible, is called <a href="https://en.wikipedia.org/wiki/Quantum_chromodynamics">quantum chromodynamics</a>. It’s a vital piece of the Standard Model, but mathematically difficult, even posing an unsolved problem of basic mathematics. We physicists do our best to calculate with it, but we’re still learning how.</p>
<p>The other aspect of the Standard Model is “<a href="https://doi.org/10.1103/PhysRevLett.19.1264">A Model of Leptons</a>.” That’s the name of the landmark 1967 paper by <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/1979/weinberg-bio.html">Steven Weinberg</a> that pulled together quantum mechanics with the vital pieces of knowledge of how particles interact and organized the two into a single theory. It incorporated the familiar electromagnetism, joined it with what physicists called “the weak force” that causes certain radioactive decays, and explained that they were different aspects of the same force. It incorporated <a href="https://www.nobelprize.org/nobel_prizes/physics/laureates/2013/higgs-facts.html">the Higgs mechanism</a> for giving mass to fundamental particles. </p>
<p>Since then, the Standard Model has predicted the results of experiment after experiment, including the discovery of several varieties of quarks and of the <a href="https://en.wikipedia.org/wiki/W_and_Z_bosons">W and Z bosons</a> – heavy particles that are for weak interactions what the photon is for electromagnetism. The possibility that <a href="https://en.wikipedia.org/wiki/Neutrino#Mass">neutrinos aren’t massless</a> was overlooked in the 1960s, but slipped easily into the Standard Model in the 1990s, a few decades late to the party.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=484&fit=crop&dpr=1 754w, https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=484&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/219960/original/file-20180522-51095-vverdp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=484&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">3D view of an event recorded at the CERN particle accelerator showing characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers).</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:3D_view_of_an_event_recorded_with_the_CMS_detector_in_2012_at_a_proton-proton_centre_of_mass_energy_of_8_TeV.png">McCauley, Thomas; Taylor, Lucas; for the CMS Collaboration CERN</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Discovering the Higgs boson in 2012, long predicted by the Standard Model and long sought after, was a thrill but not a surprise. It was yet another crucial victory for the Standard Model over the dark forces that particle physicists have repeatedly warned loomed over the horizon. Concerned that the Standard Model didn’t adequately embody their expectations of simplicity, worried about its mathematical self-consistency, or looking ahead to the eventual necessity to bring the force of gravity into the fold, physicists have made numerous proposals for theories beyond the Standard Model. These bear exciting names like <a href="https://en.wikipedia.org/wiki/Grand_Unified_Theory">Grand Unified Theories</a>, <a href="https://en.wikipedia.org/wiki/Supersymmetry">Supersymmetry</a>, <a href="https://en.wikipedia.org/wiki/Technicolor_(physics)">Technicolor</a>, and <a href="https://en.wikipedia.org/wiki/String_theory">String Theory</a>. </p>
<p>Sadly, at least for their proponents, beyond-the-Standard-Model theories have not yet successfully predicted any new experimental phenomenon or any experimental discrepancy with the Standard Model.</p>
<p>After five decades, far from requiring an upgrade, the Standard Model is <a href="http://artsci.case.edu/smat50/">worthy of celebration</a> as the Absolutely Amazing Theory of Almost Everything.</p><img src="https://counter.theconversation.com/content/94700/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Glenn Starkman receives funding from the Office of Science of the US Department of Energy. He is affiliated with Case Western Reserve University. </span></em></p>A particle physicist explains just what this keystone theory includes. After 50 years, it’s the best we’ve got to answer what everything in the universe is made of and how it all holds together.Glenn Starkman, Distinguished University Professor of Physics, Case Western Reserve UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/934582018-03-16T10:28:31Z2018-03-16T10:28:31ZBlack holes aren’t totally black, and other insights from Stephen Hawking’s groundbreaking work<figure><img src="https://images.theconversation.com/files/210672/original/file-20180315-104645-5hja7a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What goes in doesn't go out?</span> <span class="attribution"><a class="source" href="https://images.nasa.gov/details-GSFC_20171208_Archive_e000984.html">NASA Goddard</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Mathematical physicist and cosmologist Stephen Hawking was best known for his work exploring the relationship between black holes and quantum physics. A black hole is the remnant of a dying supermassive star that’s fallen into itself; these remnants contract to such a small size that gravity is so strong even light cannot escape from them. Black holes loom large in the popular imagination – schoolchildren ponder why the whole universe doesn’t collapse into one. But Hawking’s careful theoretical work filled in some of the holes in physicists’ knowledge about black holes.</p>
<h2>Why do black holes exist?</h2>
<p>The short answer is: Because gravity exists, and the speed of light is not infinite.</p>
<p>Imagine you stand on Earth’s surface, and fire a bullet into the air at an angle. Your standard bullet will come back down, someplace farther away. Suppose you have a very powerful rifle. Then you may be able to shoot the bullet at such a speed that, rather than coming down far away, it will instead “miss” the Earth. Continually falling, and continually missing the surface, the bullet will actually be in an orbit around Earth. If your rifle is even stronger, the bullet may be so fast that it leaves Earth’s gravity altogether. This is essentially what happens when we send rockets to Mars, for example.</p>
<p>Now imagine that gravity is much, much stronger. No rifle could accelerate bullets enough to leave that planet, so instead you decide to shoot light. While photons (the particles of light) do not have mass, they are still influenced by gravity, bending their path just as a bullet’s trajectory is bent by gravity. Even the heaviest of planets won’t have gravity strong enough to bend the photon’s path enough to prevent it from escaping.</p>
<p>But black holes are not like planets or stars, they are the remnants of stars, packed into the smallest of spheres, say, just a few kilometers in radius. Imagine you could stand on the surface of a black hole, armed with your ray gun. You shoot upwards at an angle and notice that the light ray instead curves, comes down and misses the surface! Now the ray is in an “orbit” around the black hole, at a distance roughly what cosmologists call the Schwarzschild radius, the “point of no return.”</p>
<p>Thus, as not even light can escape from where you stand, the object you inhabit (if you could) would look completely black to someone looking at it from far away: a black hole.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210682/original/file-20180315-104659-zihdni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hawking worked to popularize his cosmological insights.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Switzerland-Hawking-Lecture/5e88bfa19d534f04a8d826dc186bbc60/64/1">AP Photo/Keystone, Salvatore Di Nolfi</a></span>
</figcaption>
</figure>
<h2>But Hawking discovered that black holes aren’t completely black?</h2>
<p>The short answer is: Yes.</p>
<p>My previous description of black holes used the language of classical physics – basically, Newton’s theory applied to light. But the laws of physics are actually more complicated because the universe is more complicated.</p>
<p>In classical physics, the word “vacuum” means the total and complete absence of any form of matter or radiation. But in quantum physics, the vacuum is much more interesting, in particular when it is near a black hole. Rather than being empty, the vacuum is teeming with particle-antiparticle pairs that are created fleetingly by the vacuum’s energy, but must annihilate each other shortly thereafter and return their energy to the vacuum. </p>
<p>You will find all kinds of particle-antiparticle pairs produced, but the heavier ones occur much more rarely. It’s easiest to produce photon pairs because they have no mass. The photons must always be produced in pairs so they’re moving away from each other and don’t violate the law of momentum conservation.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210693/original/file-20180315-104659-xj57lw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">No light can be seen coming from a black hole outside the Schwarzschild radius.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Blackhole.png">SubstituteR</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Now imagine that a pair is created just at that distance from the center of the black hole where the “last light ray” is circulating: the Schwarzschild radius. This distance could be far from the surface or close, depending on how much mass the black hole has. And imagine that the photon pair is created so that one of the two is pointing inward – toward you, at the center of the black hole, holding your ray gun. The other photon is pointing outward. (By the way, you’d likely be crushed by gravity if you tried this maneuver, but let’s assume you’re superhuman.) </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=466&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=466&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=466&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210706/original/file-20180316-104673-1nypkw6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A pair of photons that annihilate each other is labeled A. In a second pair of photons, labeled B, one enters the black hole while the other heads outward, setting up an energy debt that is paid by the black hole.</span>
<span class="attribution"><span class="source">Christoph Adami</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Now there’s a problem: The one photon that moved inside the black hole cannot come back out, because it’s already moving at the speed of light. The photon pair cannot annihilate each other again and pay back their energy to the vacuum that surrounds the black hole. But somebody must pay the piper and this will have to be the black hole itself. After it has welcomed the photon into its land of no return, the black hole must return some of its mass back to the universe: the exact same amount of mass as the energy the pair of photons “borrowed,” according to Einstein’s famous equality E=mc².</p>
<p>This is essentially what Hawking showed mathematically. The photon that is leaving the black hole horizon will make it look as if the black hole had a faint glow: the Hawking radiation named after him. At the same time he reasoned that if this happens a lot, for a long time, the black hole might lose so much mass that it could disappear altogether (or more precisely, become visible again).</p>
<h2>Do black holes make information disappear forever?</h2>
<p>Short answer: No, that would be against the law.</p>
<p>Many physicists began worrying about this question shortly after Hawking’s discovery of the glow. The concern is this: The fundamental laws of physics guarantee that every process that happens “forward in time,” can also happen “backwards in time.”</p>
<p>This seems counter to our intuition, where a melon that splattered on the floor would never magically reassemble itself. But what happens to big objects like melons is really dictated by the laws of statistics. For the melon to reassemble itself, many gazillions of atomic particles would have to do the same thing backwards, and the likelihood of that is essentially zero. But for a single particle this is no problem at all. So for atomic things, everything you observe forwards could just as likely occur backwards. </p>
<p>Now imagine that you shoot one of two photons into the black hole. They only differ by a marker that we can measure, but that does not affect the energy of the photon (this is called a “polarization”). Let’s call these “left photons” or “right photons.” After the left or right photon crosses the horizon, the black hole changes (it now has more energy), but it changes in the same way whether the left or right photon was absorbed.</p>
<p>Two different histories now have become one future, and such a future cannot be reversed: How would the laws of physics know which of the two pasts to choose? Left or right? That is the violation of time-reversal invariance. The law requires that every past must have exactly one future, and every future exactly one past. </p>
<p>Some physicists thought that maybe the Hawking radiation carries an imprint of left/right so as to give an outside observer a hint at what the past was, but no. The Hawking radiation comes from that flickering vacuum surrounding the black hole, and has nothing to do with what you throw in. All seems lost, but not so fast. </p>
<p>In 1917, Albert Einstein showed that matter (even the vacuum next to matter) actually does react to incoming stuff, in a very peculiar way. The vacuum next to that matter is “tickled” to produce a particle-antiparticle pair that looks like an exact copy of what just came in. In a very real sense, the incoming particle stimulates the matter to create a pair of copies of itself – actually a copy and an anti-copy. Remember, random pairs of particle and antiparticle are created in the vacuum all the time, but the tickled-pairs are not random at all: They look just like the tickler.</p>
<p>This copy process is known as the “stimulated emission” effect and is at the origin of all lasers. The Hawking glow of black holes, on the other hand, is just what Einstein called the “spontaneous emission” effect, taking place near a black hole.</p>
<p>Now imagine that the tickling creates this copy, so that the left photon tickles a left photon pair, and a right photon gives a right photon pair. Since one partner of the tickled pairs must stay outside the black hole (again from momentum conservation), that particle creates the “memory” that is needed so that information is preserved: One past has only one future, time can be reversed, and the laws of physics are safe.</p>
<p>In a cosmic accident, Hawking died on Einstein’s birthday, whose theory of light – it just so happens – saves Hawking’s theory of black holes.</p><img src="https://counter.theconversation.com/content/93458/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christoph Adami receives funding from the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the Templeton Foundation. </span></em></p>The famous cosmologist was closely identified with black holes due to his revolutionary theoretical work explaining some of their mysterious properties.Christoph Adami, Professor of Physics and Astronomy & Professor of Microbiology and Molecular Genetics, Michigan State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/888012017-12-18T18:33:31Z2017-12-18T18:33:31ZWater-dwelling organisms show new ways to harvest light for solar tech<figure><img src="https://images.theconversation.com/files/198308/original/file-20171208-27674-a2n4oj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Diatoms - like those seen under a microscope here - can teach us a lot about harvesting light.</span> <span class="attribution"><span class="source">Rattiya Thongdumhyu/Shutterstock</span></span></figcaption></figure><p>Photosynthesis is a great source <a href="https://theconversation.com/a-smart-switch-in-photosynthesis-holds-lessons-for-solar-technology-66602">of inspiration</a> for solar technology. By studying the minutiae of how plants convert light into useful forms of energy, scientists can better mimic nature’s clever solutions for cleaner energy production.</p>
<p>More than half of our planet’s photosynthetic energy conversion takes place in water. <a href="https://www.britannica.com/science/diatom">Diatoms</a>, which are the equivalent of grass in the sea because of their great abundance and importance, are responsible for most of this water-based photosynthesis. Diatoms are single-celled organisms that can take on an incredible variety of shapes and sizes and are a very common form of phytoplankton, the organisms in the plankton community that produce their own food.</p>
<p>Diatoms harvest light in much the same way that grass and most other plants do. But there’s a subtle difference in the relative orientation of three particular light-absorbing molecules in diatoms that sets them apart from their counterparts on land. </p>
<p>This structural difference means that the state of energy generated in diatoms immediately after light absorption should be susceptible to small deformations in their light harvesting apparatus. Large amounts of energy should be lost as a result. Instead, diatoms’ initial energy flow is very efficient and robust.</p>
<p>Until now, nobody has been able to explain this contradiction. Now a team with scientists from the Netherlands, Germany and Czech Republic – and myself, from South Africa – have managed to <a href="http://www.pnas.org/content/early/2017/12/05/1714656115.abstract">resolve this conundrum</a>. </p>
<p>Diatoms’ light-harvesting systems use multiple methods to circumvent energy traps. Our findings have important implications for the latest solar cell technologies; scientists are always looking for ways to avoid large energy losses in inexpensive materials, and diatoms’ tricks may offer new insights to keep cheap solar cells running efficiently and robustly throughout their processes.</p>
<h2>How to avoid an energy trap</h2>
<p>The very first step of photosynthesis involves the absorption of a photon – a particle of light. The photon is then converted into an excited state, a process which occurs in one of the plant’s antenna systems. These systems consist of a dense arrangement of light-absorbing molecules known as chromophores, bound to a protein scaffold.</p>
<p>The antenna systems’ main purpose is to ensure that, once photons have been converted into excited states, they reach a reaction centre in the plant where the energy can be converted into a more stable form. On their way to the reaction centre, the excitation energy must avoid temporal or permanent energy traps that will prevent them from reaching the reaction centre on time and the energy being lost.</p>
<p>Plants’ clever light-harvesting systems gear up to dodge those energy traps by sharing the photons’ energy among several chromophores. This type of extended or spread energy state is called an <a href="https://www.britannica.com/science/exciton">“exciton”</a> and it has several advantages. </p>
<p>For example, it does not easily get stuck in an energy trap. It’s like playing lawn bowls on a rough terrain: a golf ball will not get far, but a large ball is much less affected by holes and bumps in the grass. In the same way, excitons will not be easily caught or affected by an energy trap. They are efficient and robust.</p>
<p>Excitons also naturally create an energy gradient, which ensures that energy flows in one direction – straight to a spot in the plant’s light-harvesting antenna from which it can be passed on and eventually stored for future use. </p>
<p>Diatoms’ light-harvesting antennae work differently, and that’s what interested us.</p>
<p>They don’t use large excitons at a key position in their light-harvesting antennae. This suggests that the excitation energy will be quickly trapped and lost. We observed trapping, as we’d expected; but, remarkably, the energy was not lost. </p>
<p>Instead, diatoms have a special antenna structure that deposits the excitation energy in a unique state where it is less likely to be lost. The flow of energy is extremely sensitive to structural disorder – ubiquitous vibrations of the protein structure – but diatoms’ antennae react to the disorder in a positive way to harvest light efficiently. This kind of disorder is often equated with noise or messiness: so nature has showed us a way to use a “bad” thing for a “good” purpose. </p>
<p>This is good news because now we know that there is not only one solution to the important problem of preserving an excited state for a long time in a “messy” environment. For instance, the result could be applied in the world of quantum computing, where information has to be stored for a long time at room temperature. During this time it is strongly susceptible to a noisy environment.</p>
<h2>Learning from nature</h2>
<p>Excitons are pervasive in solar technologies. As there is a drive towards more abundant, natural, inexpensive materials for solar technologies, disorder in the materials becomes an increasingly more important constraint to deal with. </p>
<p>Some of these materials use polymers or organic materials, which exhibit structural disorder just like the proteins in the photosystems of plants and diatoms do. Inexpensive semiconductor-based materials contain a lot of defects, which often serve as energy-trapping centres. And light-absorbing molecules or nanostructures are being used more and more in solar technologies; these exhibit exciton states that are quite similar to those in the photosynthetic antennae.</p>
<p>We need to find ways of overcoming the adverse effects of disorder on excitons, or valuable energy will be lost. Our findings demonstrate that there may be multiple solutions to this problem.</p><img src="https://counter.theconversation.com/content/88801/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tjaart Krüger receives funding from the University of Pretoria, the Department of Science and Technology and the National Research Foundation.</span></em></p>Diatoms’ tricks may offer new insights that keep solar cell energy running efficiently and robustly throughout their processes.Tjaart Krüger, Associate Professor in Biophysics, University of PretoriaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/743552017-05-26T01:32:59Z2017-05-26T01:32:59ZHow do the chemicals in sunscreen protect our skin from damage?<figure><img src="https://images.theconversation.com/files/171062/original/file-20170525-23230-m46xg5.jpg?ixlib=rb-1.1.0&rect=0%2C98%2C2000%2C1419&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Don't skimp on the SPF.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/toned-photo-kid-beach-smooth-skin-381581356">Sabphoto via Shutterstock.com</a></span></figcaption></figure><p>Not so long ago, people like my Aunt Muriel thought of sunburn as a necessary evil on the way to a “good base tan.” She used to slather on the baby oil while using a large reflector to bake away. Aunt Muriel’s mantra when the inevitable burn and peel appeared: Beauty has its price.</p>
<p>Was she ever right about that price – but it was a lot higher than any of us at the time recognized. What sun addicts didn’t know then was that we were setting our skin up for damage to its structural proteins and DNA. Hello, wrinkles, liver spots and cancers. No matter <a href="https://doi.org/10.1001/archderm.1988.01670060015008">where your complexion falls</a> on the <a href="http://www.skincancer.org/prevention/are-you-at-risk/fitzpatrick-skin-quiz">Fitzpatrick Skin Type</a> scale, ultraviolet radiation (UV) from the sun or tanning beds will damage your skin.</p>
<p>Today, recognition of the risks posed by UV rays has motivated scientists, myself included, to study what’s going on in our cells when they’re in the sun – and devise modern ways to ward off that damage.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=236&fit=crop&dpr=1 600w, https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=236&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=236&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=297&fit=crop&dpr=1 754w, https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=297&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/170967/original/file-20170525-23279-110s6q8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=297&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">UV light that affects our skin has a shorter wavelength than the parts of the electromagnetic spectrum we can see.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:EM_Spectrum_Properties_edit.svg">Inductiveload, NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>What happens when sun hits skin</h2>
<p>Sunlight is composed of packets of energy called photons. The visible colors we can see by eye are relatively harmless to our skin; it’s the sun’s ultraviolet (UV) light photons that can cause skin damage. UV light can be broken down into two categories: UVA (in the wavelength range 320-400 nanometers) and UVB (in the wavelength range 280–320 nm). </p>
<p><iframe id="Niww2" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/Niww2/8/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Our skin contains molecules that are perfectly structured to absorb the energy of UVA and UVB photons. This puts the molecule into an energetically excited state. And as the saying goes, what goes up must come down. In order to release their acquired energy, these molecules undergo chemical reactions – and in the skin that means there are biological consequences.</p>
<p>Interestingly, some of these effects used to be considered helpful adaptations – though we now recognize them as forms of damage. Tanning is due to the production of <a href="https://www.derm101.com/inflammatory/embryologic-histologic-and-anatomic-aspects/melanocytes/">extra melanin pigment induced by UVA rays</a>. Exposure to the sun also turns on the skin’s natural antioxidant network, which <a href="http://www.nature.com/nchembio/journal/v10/n7/pdf/nchembio.1548.pdf">deactivates highly destructive reactive oxygen species (ROS) and free radicals</a>; if left unchecked, these can cause cellular damage and oxidative stress within the skin.</p>
<p>We also know that UVA light penetrates deeper into the skin than UVB, destroying a structural protein called collagen. As collagen degrades, our skin loses its elasticity and smoothness, leading to wrinkles. UVA is responsible for many of the visible signs of aging, while UVB light is considered the primary source of sunburn. Think “A” for aging and “B” for burning.</p>
<p>DNA itself can absorb both <a href="http://www.pnas.org/content/103/37/13765.short">UVA and UVB rays, causing mutations</a> which, if unrepaired, can lead to non-melanoma (basal cell carcinoma, squamous cell carcinoma) or <a href="https://doi.org/10.1126/science.1253735">melanoma skin cancers</a>. Other skin molecules pass absorbed UV energy on to those highly reactive ROS and free radicals. The resulting oxidative stress can overload the skin’s built-in antioxidant network and cause cellular damage. ROS can react with DNA, forming mutations, and with collagen, leading to wrinkles. They can also interrupt cell signaling pathways and gene expression.</p>
<p>The end result of all of these photoreactions is photodamage that accumulates over the course of a lifetime from repeated exposure. And – this cannot be emphasized enough — this applies to all skin types, from Type I (like Nicole Kidman) to Type VI (like Jennifer Hudson). <a href="http://www.skincancer.org/skin-cancer-information/skin-cancer-facts">Regardless of how much melanin we have in our skin</a>, we can develop UV-induced skin cancers and we will all eventually see the signs of photo-induced aging in the mirror.</p>
<h2>Filtering photons before the damage is done</h2>
<p>The good news, of course, is that the risk of skin cancer and the visible signs of aging can be minimized by preventing overexposure to UV radiation. When you can’t avoid the sun altogether, today’s sunscreens have got your back (and all the rest of your skin too).</p>
<p>Sunscreens employ UV filters: molecules specifically designed to help reduce the amount of UV rays that reach through the skin surface. A film of these molecules forms a protective barrier either absorbing (chemical filters) or reflecting (physical blockers) UV photons before they can be absorbed by our DNA and other reactive molecules deeper in the skin. </p>
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<p>In the United States, the Food and Drug Administration regulates sunscreens as drugs. Because we were historically most concerned with protecting against sunburn, <a href="http://dx.doi.org/10.1016/j.jaad.2010.01.005">14 molecules that block sunburn-inducing UVB rays</a> are approved for use. That we have just two UVA-blocking molecules available in the United States – avobenzone, a chemical filter; and zinc oxide, a physical blocker – is a testament to our more recent understanding that UVA causes trouble, not just tans.</p>
<p>The FDA also has enacted <a href="https://www.federalregister.gov/documents/2011/06/17/2011-14766/labeling-and-effectiveness-testing-sunscreen-drug-products-for-over-the-counter-human-use">strict labeling requirements</a> – most obviously about SPF (sun protection factor). On labels since 1971, SPF represents the relative time it takes for an individual to get sunburned by UVB radiation. For example, if it takes 10 minutes typically to burn, then, if used correctly, an SPF 30 sunscreen should provide 30 times that – 300 minutes of protection before sunburn. </p>
<p>“Used correctly” is the key phrase. Research shows that it takes about one ounce, or basically a <a href="https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs">shot glass-sized amount of sunscreen</a>, to cover the exposed areas of the average adult body, and a nickel-sized amount for the face and neck (more or less, depending on your body size). The majority of people apply between a <a href="https://www.ncbi.nlm.nih.gov/pubmed/12374537">quarter to a half of the recommended amounts</a>, placing their skin at risk for sunburn and photodamage.</p>
<p>In addition, sunscreen efficacy decreases in the water or with sweating. To help consumers, FDA now requires sunscreens labeled <a href="https://www.federalregister.gov/documents/2011/06/17/2011-14766/labeling-and-effectiveness-testing-sunscreen-drug-products-for-over-the-counter-human-use">“water-resistant” or “very water-resistant”</a> to last up to 40 minutes or 80 minutes, respectively, in the water, and the <a href="https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs">American Academy of Dermatology</a> and other medical professional groups <a href="https://www.cancer.org/cancer/skin-cancer/prevention-and-early-detection/uv-protection.html">recommend reapplication immediately after any water sports</a>. The general <a href="https://www.aad.org/media/stats/prevention-and-care/sunscreen-faqs">rule of thumb</a> is to reapply about every two hours and certainly after water sports or sweating.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/171063/original/file-20170525-23234-v4lxdi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">In the U.S., the FDA regulates sunscreens available to consumers.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/alameda-ca-june-05-2016-store-433399849">Sheila Fitzgerald via Shutterstock.com</a></span>
</figcaption>
</figure>
<p>To get high SPF values, multiple UVB UV filters are combined into a formulation based upon <a href="https://www.federalregister.gov/documents/2011/06/17/2011-14766/labeling-and-effectiveness-testing-sunscreen-drug-products-for-over-the-counter-human-use">safety standards set by the FDA</a>. However, the SPF doesn’t account for UVA protection. For a sunscreen to make a claim as having UVA and UVB protection and be labeled “Broad Spectrum,” it must pass <a href="https://www.fda.gov/drugs/guidancecomplianceregulatoryinformation/guidances/ucm330694.htm">FDA’s Broad Spectrum Test</a>, where the sunscreen is hit with a large dose of UVB and UVA light before its effectiveness is tested. </p>
<p>This pre-irradiation step was established in <a href="https://www.fda.gov/drugs/guidancecomplianceregulatoryinformation/guidances/ucm330694.htm">FDA’s 2012 sunscreen labeling rules</a> and acknowledges something significant about UV-filters: some can be photolabile, meaning they can degrade under UV irradiation. The most famous example may be <a href="http://onlinelibrary.wiley.com/doi/10.1046/j.1440-0960.1999.00319.x/full">PABA</a>. This UVB-absorbing molecule is rarely used in sunscreens today because it forms photoproducts that elicit an allergic reaction in some people.</p>
<p>But the Broad Spectrum Test really came into effect only once the UVA-absorbing molecule avobenzone came onto the market. Avobenzone can interact with octinoxate, a strong and widely used UVB absorber, in a way that makes avobenzone less effective against UVA photons. The UVB filter octocrylene, on the other hand, helps stabilize avobenzone so it lasts longer in its UVA-absorbing form. Additionally, you may notice on some sunscreen labels the molecule ethylhexyl methoxycrylene. It helps stabilize avobenzone even in the presence of octinoxate, and provides us with longer-lasting protection against UVA rays.</p>
<p>Next up in sunscreen innovation is the broadening of their mission. Because even the highest SPF sunscreens don’t block 100 percent of UV rays, the addition of antioxidants can supply a second line of protection when the skin’s natural antioxidant defenses are overloaded. Some antioxidant ingredients my colleagues and I have worked with include <a href="http://www.springer.com/us/book/9783319293813">tocopheral acetate (Vitamin E), sodium ascorbyl phosophate (Vitamin C), and DESM</a>. And sunscreen researchers are beginning to investigate if the <a href="http://www.springer.com/us/book/9783319293813">absorption of other colors of light</a>, like infrared, by skin molecules has a role to play in photodamage.</p>
<p>As research continues, one thing we know for certain is that protecting our DNA from UV damage, for people of every color, is synonymous with preventing skin cancers. The Skin Cancer Foundation, American Cancer Society and the American Academy of Dermatology all stress that research shows regular use of an SPF 15 or higher sunscreen prevents sunburn and reduces the risk of <a href="http://dx.doi.org/10.1016/S0140-6736(98)12168-2">non-melanoma cancers by 40 percent</a> and <a href="https://doi.org//10.1200/jco.2010.28.7078">melanoma by 50 percent</a>.</p>
<p>We can still enjoy being in the sun. Unlike my Aunt Muriel and us kids in the 1980s, we just need to use the resources available to us, from long sleeves to shade to sunscreens, in order to protect the molecules in our skin, especially our DNA, from UV damage.</p><img src="https://counter.theconversation.com/content/74355/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kerry Hanson has consulted for Bayer, J&J/Neutrogena, and P&G. Her academic work has been funded by Hallstar and through a joint University of California Discovery Grant with Merck. She is a member of the American Chemical Society. </span></em></p>Energy from the sun’s rays can cause skin damage and cancers. Sunscreens can absorb or reflect the dangerous UV light. Here’s how it works.Kerry Hanson, Research Chemist, University of California, RiversideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/746022017-03-30T06:13:18Z2017-03-30T06:13:18ZThe world’s first glow-in-the-dark frog found in Argentina<figure><img src="https://images.theconversation.com/files/162094/original/image-20170322-31217-183kp0s.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A male Hypsiboas punctatus frog in daylight.</span> <span class="attribution"><a class="source" href="https://upload.wikimedia.org/wikipedia/commons/c/ca/Hypsiboas_punctatus_Peru_02.JPG">Erfil/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Scientists in Argentina have discovered a frog that glows in moonlight and at twilight. Fluorescence in terrestrial environments had previously only been traced to a few species of insects and birds and had never been scientifically reported in any of the world’s 7,000-plus amphibian species.</p>
<p>A team of herpetologists made the <a href="http://www.nature.com/news/first-fluorescent-frog-found-1.21616">headline-grabbing discovery</a> in the outskirts of the city of Santa Fe, Argentina, while collecting frogs to research the biochemical <em>cloricia</em> in amphibians. They sought out the polka-dot tree frog (<em>Hypsiboas punctatus</em>), a species found throughout South America, because its translucent skin allows the <a href="https://en.wikipedia.org/wiki/Polka-dot_tree_frog">accumulation of biliverdin</a> (a blue-green bile pigment) to be seen with the naked eye.</p>
<p>But when they shone a UVA light on the frogs, they did not see the faint red biliverdin emission they had anticipated. Rather, what they saw was a bright and beautiful cyan fluorescence. So luminous were the frogs that under the black light they glowed in the dark, helping the scientists locate specimens. This fluorescence was present in all of the 100-plus polka-dot tree frogs collected.</p>
<p>The team included researchers from the <a href="http://www.macn.secyt.gov.ar/cont_Gral/home.php">Bernardino Rivadavia Argentine Museum of Natural Sciences-CONICET</a>, the <a href="http://exactas.uba.ar/">University of Buenos Aires</a>, the <a href="http://www.leloir.org.ar/en/">Instituto Leloir Foundation</a> and <a href="http://www.inquimae.fcen.uba.ar/">INQUIMAE-CONICET</a> in Argentina and Brazil’s <a href="http://fcfrp.usp.br/pg/pcf/en/">University of São Paulo Faculty of Pharmaceutical Sciences of Ribeirão Preto</a>.</p>
<h2>Luminous in the moonlight</h2>
<p>The polka-dot tree frog’s translucent skin appears to glow because it allows a high level of transmission of light in the green and red parts of the electromagnetic spectrum, while blocking transmission of blue light.</p>
<p>The peculiar cyan fluorescence, which we found originated in its skin glands and lymph nodes, belongs to a family of derivatives of the molecule dihydroisoquinolinone. The compounds were named <a href="http://dx.doi.org/10.1073/pnas.1701053114">“hyloins”</a>, after the amphibian family Hylidae, to which the tree frog belongs.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162274/original/image-20170323-4930-1rvlcpu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The polka-dot tree frog seen in daylight, above, and glowing under black light, below.</span>
<span class="attribution"><span class="source">Julián Faivovich and Carlos Taboada</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Fluorescence can be an important biosignal for visual communication, helping these frogs locate each other. The perceived brightness depends on several factors: the proportion of photons arising from fluorescence compared to those reflected by the animal; the spectral lighting conditions of the environment where the amphibians live; and the sensitivity of frogs’ eyes to different colours.</p>
<p>In the case of <em>Hypsiboas punctatus</em>, we found that under twilight-nocturnal conditions, between 18% and 30% of all the light (photons) emanating from the frog’s skin were florescent. That’s a substantial proportion, enough to add significant fluorescence to the typical green (in daylight) colouration of the frog, enhancing its visibility.</p>
<p>Finding fluorescence in a land animal is particularly interesting because it has been <a href="http://pubs.rsc.org/-/content/articlelanding/2015/pp/c5pp00122f/unauth#!divAbstract">generally considered irrelevant</a> but for its presence in some insects (spiders, scorpions, beetles, butterflies, moths, dragonflies, millipedes) and in two avian species, parrots and parrotlets. In parrotlets, differences in feather fluorescence between sexes <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.2012.00931.x/abstract">have been found to serve</a> a function in mating and attraction.</p>
<p>With the polka-dot tree frog, we expect that its fluorescence plays a role in inter-species visual communication (because it matches the sensitivity of the frogs’ eyes photoreceptors for blue and green). We do not believe that it has any relevance to mating, as florescence does not seem to differ between females and males.</p>
<h2>What else glows?</h2>
<p>The discovery of fluorescence in frogs – a species previously unknown to exhibit it – has renewed interest in searching for other glow-in-the-dark amphibians.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=500&fit=crop&dpr=1 600w, https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=500&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=500&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=628&fit=crop&dpr=1 754w, https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=628&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/162262/original/image-20170323-4924-ntlsn0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=628&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Beetles also display fluorescence.</span>
</figcaption>
</figure>
<p>The finding also opens additional avenues for future research. A more detailed study on the spectral sensitivity of the eye photoreceptors of <em>Hypsiboas punctatus</em>, for example, would help us calculate the amount of light reaching each of the polka-dot tree frog’s photoreceptors and better understand the species’ visual perception.</p>
<p>We are also interested in evaluating the photophysical properties of the purified free fluorophores found in this study, including their chemical and biochemical makeup. They could potentially be used as fluorescent markers or labels in molecular biology or biotechnology, allowing <a href="https://en.wikipedia.org/wiki/Fluorescent_tag">microscopic detection of biomolecules</a>.</p>
<p>Finally, this discovery has given scientists a strong hint for the answer to an important question in biophotophysical research: does naturally occurring fluorescence act as a biosignal, or is it simply a non-functional outcome of certain pigments’ chemical structure?</p>
<p>The polka-dot tree frog’s moonlight glow suggests strongly that, yes, fluorescence matters.</p>
<hr>
<p><em>Scientists involved in this work were: Carlos Taboada (Bernardino Rivadavia Argentina Museum of Natural Sciences-CONICET and the University of Buenos Aires, INQUIMAE-CONICET); Andrés E. Brunetti (Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo); Federico N. Pedron (University of Buenos Aires, INQUIMAE-CONICET and the Department of Inorganic, Analytic and Physical Chemical Chemistry, FCEN); Fausto Carnevale Neto (Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo); Darío A. Estrin (University of Buenos Aires, INQUIMAE-CONICET and the Department of Inorganic, Analytic and Physical Chemical Chemistry, FCEN); Sara E. Bari (University of Buenos Aires, INQUIMAE-CONICET); Lucía B. Chemes (Protein Structure-Function and Engineering Laboratory, Fundación Instituto Leloir and Instituto de Investigaciones Bioquímicas de Buenos Aires-CONICET); Norberto Peporine Lopes (Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo); María G. Lagorio (University of Buenos Aires, INQUIMAE-CONICET and the Department of Inorganic, Analytic and Physical Chemical Chemistry, FCEN); and Julián Faivovich (Bernardino Rivadavia Argentina Museum of Natural Sciences-CONICET and University of Buenos Aires Department of Biodiversity and Biologial Experimentation, FCEN).</em></p><img src="https://counter.theconversation.com/content/74602/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>María Gabriela Lagorio does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists in Argentina have discovered a frog that glows in moonlight and at twilight.María Gabriela Lagorio, Researcher and Professor, Bioespectroscopy and Biophotochemistry, Universidad de Buenos AiresLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/689032016-11-29T02:25:35Z2016-11-29T02:25:35ZThe future of electronics is light<figure><img src="https://images.theconversation.com/files/147248/original/image-20161123-19717-hrc3xx.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A basic design of a light-based chip.</span> <span class="attribution"><span class="source">Arnab Hazari</span>, <span class="license">Author provided</span></span></figcaption></figure><p>For the past four decades, the electronics industry has been driven by what is called “<a href="http://www.mooreslaw.org/">Moore’s Law</a>,” which is not a law but more an axiom or observation. Effectively, it suggests that the electronic devices double in speed and capability about every two years. And indeed, every year tech companies come up with new, faster, smarter and better gadgets.</p>
<p>Specifically, Moore’s Law, as articulated by Intel cofounder Gordon Moore, is that “The number of transistors incorporated in a chip will <a href="https://www-ssl.intel.com/content/www/us/en/history/museum-gordon-moore-law.html">approximately double every 24 months</a>.” Transistors, tiny electrical switches, are the fundamental unit that drives all the electronic gadgets we can think of. As they get smaller, they also <a href="http://www.intel.com/content/www/us/en/silicon-innovations/moores-law-technology.html">get faster and consume less electricity</a> to operate.</p>
<p>In the technology world, one of the biggest questions of the 21st century is: How small can we make transistors? If there is a limit to how tiny they can get, we might reach a point at which we can no longer continue to make smaller, more powerful, more efficient devices. It’s an industry with <a href="https://www.statista.com/statistics/272115/revenue-growth-ce-industry/">more than US$200 billion</a> in annual revenue in the U.S. alone. Might it stop growing?</p>
<h2>Getting close to the limit</h2>
<p>At the present, companies like Intel are mass-producing transistors <a href="https://www-ssl.intel.com/content/www/us/en/silicon-innovations/intel-14nm-technology.html">14 nanometers across</a> – just 14 times wider than <a href="https://dx.doi.org/10.1016/0022-2836(81)90099-1">DNA molecules</a>. They’re made of silicon, the <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/elabund.html">second-most abundant material</a> on our planet. Silicon’s atomic size is <a href="http://www.extremetech.com/computing/97469-is-14nm-the-end-of-the-road-for-silicon-lithography">about 0.2 nanometers</a>.</p>
<p>Today’s transistors are about 70 silicon atoms wide, so the possibility of making them even smaller is itself shrinking. We’re getting very close to the limit of how small we can make a transistor.</p>
<p>At present, transistors use electrical signals – electrons moving from one place to another – to communicate. But if we could use light, made up of photons, instead of electricity, we could make transistors even faster. My work, on finding ways to integrate light-based processing with existing chips, is part of that nascent effort.</p>
<h2>Putting light inside a chip</h2>
<p>A <a href="https://reibot.org/2011/09/06/a-beginners-guide-to-the-mosfet/">transistor has three parts</a>; think of them as parts of a digital camera. First, information comes into the lens, analogous to a transistor’s source. Then it travels through a channel from the image sensor to the wires inside the camera. And lastly, the information is stored on the camera’s memory card, which is called a transistor’s “drain” – where the information ultimately ends up.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=550&fit=crop&dpr=1 600w, https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=550&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=550&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=691&fit=crop&dpr=1 754w, https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=691&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/147791/original/image-20161128-22729-tc0olq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=691&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Light waves can have different frequencies.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:VisibleEmrWavelengths.svg">maxhurtz</a></span>
</figcaption>
</figure>
<p>Right now, all of that happens by moving electrons around. To substitute light as the medium, we actually need to move photons instead. Subatomic particles like electrons and photons travel in a wave motion, vibrating up and down even as they move in one direction. The length of each wave depends on what it’s traveling through. </p>
<p>In silicon, the most efficient wavelength for photons is <a href="http://www.its.bldrdoc.gov/fs-1037/dir-040/_5927.htm">1.3 micrometers</a>. This is very small – a human hair is <a href="http://www.nano.gov/nanotech-101/what/nano-size">around 100 micrometers across</a>. But <a href="http://homepages.rpi.edu/%7Esawyes/Models_review.pdf">electrons in silicon</a> are even smaller – with wavelengths <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/debrog2.html">50 to 1,000 times shorter</a> than photons.</p>
<p>This means the equipment to handle photons needs to be bigger than the electron-handling devices we have today. So it might seem like it would force us to build larger transistors, rather than smaller ones.</p>
<p>However, for two reasons, we could keep chips the same size and deliver more processing power, shrink chips while providing the same power, or, potentially both. First, a <a href="http://www.nature.com/lsa/focus/circuits/index.html">photonic chip</a> needs only a few light sources, generating photons that can then be directed around the chip with very small lenses and mirrors.</p>
<p>And second, light is much faster than electrons. On average photons can travel about <a href="http://education.jlab.org/qa/electron_01.html">20 times faster</a> than electrons in a chip. That means computers that are 20 times faster, a speed increase that would take about 15 years to achieve with current technology.</p>
<p>Scientists have demonstrated <a href="http://www.nature.com/lsa/focus/circuits/index.html">progress toward photonic chips</a> in recent years. A key challenge is making sure the new light-based chips can work with all the existing electronic chips. If we’re able to figure out how to do it – or even to use light-based transistors to enhance electronic ones – we could see significant performance improvement.</p>
<h2>When can I get a light-based laptop or smartphone?</h2>
<p>We still have some way to go before the first consumer device reaches the market, and progress takes time. The first transistor was made in the year 1907 using vacuum tubes, which were <a href="http://www.edisontechcenter.org/VacuumTubes.html">typically between one and six inches tall</a> (on average 100 mm). By 1947, the current type of transistor – the one that’s now just 14 nanometers across – was invented and it was <a href="https://en.wikipedia.org/wiki/History_of_the_transistor#The_first_transistor">40 micrometers long</a> (about 3,000 times longer than the current one). And in 1971 the first commercial microprocessor (the powerhouse of any electronic gadget) was <a href="https://en.wikipedia.org/wiki/Intel_4004">1,000 times bigger</a> than today’s when it was released.</p>
<p>The vast research efforts and the consequential evolution seen in the electronics industry are only starting in the photonic industry. As a result, current electronics can perform tasks that are far more complex than the best current photonic devices. But as research proceeds, light’s capability will catch up to, and ultimately surpass, electronics’ speeds. However long it takes to get there, the future of photonics is bright.</p><img src="https://counter.theconversation.com/content/68903/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arnab Hazari's research group receives funding from the National Science Foundation, under MRSEC program.</span></em></p>As electronic transistors get tinier, they approach a point at which they won’t be able to get smaller. How can we keep shrinking our devices, and making them more powerful at the same time? Light.Arnab Hazari, Ph.D. student in Electrical Engineering, University of MichiganLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/662102016-09-29T06:36:10Z2016-09-29T06:36:10ZHold it right there: how (and why) to stop light in its tracks<figure><img src="https://images.theconversation.com/files/139710/original/image-20160929-27051-13s7aly.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A visualisation of simulation data showing light successfully trapped at a standstill.</span> <span class="attribution"><span class="license">Author provided</span></span></figcaption></figure><p>We are taught in school that the speed of light is a universal constant. Yet we also know that light travels more slowly through materials such as water and glass. Recently, we have even discovered that light can <a href="http://www.abc.net.au/news/2016-09-27/scientists-stop-light-like-star-wars-in-cloud-of-atoms/7867344">actually be made to stand completely still</a>.</p>
<p>In fact, it was first done a long time ago … in a galaxy far, far away. In a scene from the <a href="http://www.imdb.com/title/tt2488496/">latest Star Wars film</a>, Kylo Ren stops a blaster pulse using The Force. The pulse is frozen, shimmering in mid-air. More recently, for <a href="http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys3901.html">our paper published in Nature Physics this week</a>, we stopped a pulse of laser light using a rather different method, by trapping it in a cloud of cold rubidium atoms.</p>
<p>Rubidium and other similar atoms have been used previously to <a href="http://www.nature.com/news/2001/010119/full/news010125-3.html">slow down and store light</a> and even to <a href="http://www.nature.com/nature/journal/v426/n6967/full/nature02176.html">trap it</a>. These systems all work by absorbing and re-emitting laser light from the atoms in a controlled way. </p>
<p>But we found a new way to trap light, by using the light to write a particular “shape” into the atoms. When the light was re-emitted, it became trapped in the atoms. It turned out that once we had picked the right directions and frequencies for our lasers, the experiment was pretty straightforward. The hard part was figuring out the right frequencies and directions!</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/139708/original/image-20160929-27014-1biw49v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A cloud of rubidium atoms inside a vacuum chamber was used to slow the light to a standstill.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Embracing entanglement</h2>
<p>Why do this? We are interested in trapping light because our ultimate goal is to make individual light particles, or photons, interact with one another. By interacting directly, the photons will become entangled. By scaling this up to many interactions, involving many photons, we could theoretically create the intricate states of information necessary for powerful <a href="https://theconversation.com/au/topics/quantum-computing-525">quantum computing</a>. </p>
<p>Unfortunately, photons interact incredibly weakly with each other, but they can interact more strongly if they can be confined in a particular material long enough to enhance the interaction to a more useful level. In fact, these sorts of interactions have recently been <a href="http://www.nature.com/nphys/journal/v11/n11/abs/nphys3433.html">demonstrated</a> by <a href="http://www.pnas.org/content/113/35/9740.abstract">multiple</a> research <a href="http://advances.sciencemag.org/content/2/4/e1600036.full">groups</a> around the world, often by using atom clouds to confine the light. But, as I’ll explain below, our new stationary light system may have advantages when it comes to getting photons to interact.</p>
<h2>Light switch</h2>
<p>Quantum computing is an exciting and rapidly evolving field of research, and our team is part of the Australian Research Council’s Centre for Quantum Computation and Communication Technology. There are many different potential platforms for quantum computing. For example, the centre’s UNSW team has demonstrated quantum computing operations <a href="https://www.engineering.unsw.edu.au/news/quantum-computing-first-two-qubit-logic-gate-in-silicon">using phosphorus atoms embedded in silicon chips</a>. </p>
<p>But our group mainly studies light, not least because it is very likely that light will play some role in quantum computers. It offers a convenient way to send quantum information within or between computers because, unlike atoms or electric currents, it is not vulnerable to stray magnetic or electric fields. It may even be possible to perform quantum computation using light, and this is the idea that motivates our research into stationary light.</p>
<p>Our team has been able to store and retrieve pulses of light in the same system. We have also <a href="https://www.osapublishing.org/optica/abstract.cfm?uri=optica-3-1-100">been able to show</a> that quantum information encoded in these light pulses is preserved – meaning that it can form the basis of computing memory.</p>
<p>However, this is not sufficient to generate the sort of interaction we want, because the light is entirely absorbed into the atoms and it can no longer interact. Instead, we need to trap light in the memory, not just store it.</p>
<p>While researching how to trap light in the atomic memory, I discovered using a computer simulation that a particular kind of shape written into the atomic memory would produce stationary light. By retrieving the light in two directions at once, the light could actually be trapped in the memory. All the light being re-emitted throughout the memory would destructively interfere at the ends of the memory and not escape.</p>
<p>The simulations also predicted other interesting behaviour: if the wrong shape was written, some light would escape, but the memory would rapidly evolve to a shape where the light is trapped. This could be useful for stationary light by making it more robust, but it may also be useful for other optical processing.</p>
<p>We were able to demonstrate all of this behaviour experimentally using our atomic memory. Unlike Kylo Ren’s frozen blaster pulse, it was not possible to see the stationary light directly (to see something, photons have to travel from the object to your eyes, and these photons were not going anywhere). Instead, the fact the behaviour of the system matched our predictions so precisely confirmed that the light was indeed stationary.</p>
<p>Light has previously been trapped in a similar system. What makes our system new and interesting is that we believe it is the most convincing demonstration so far, but also that the behaviour of our stationary light is radically different. We believe that this new behaviour, where the light travels more freely through the memory, could allow for stronger nonlinear interactions.</p>
<p>This experiment is only a single step on the long road to optical quantum computing. The next step will be to prove that photons can indeed interact with one another within our system. Looking much further down the road, we hope this will give rise to a device that can use some of our discoveries, among many others, to generate the intricate states of many entangled photons necessary for an optical quantum computer.</p><img src="https://counter.theconversation.com/content/66210/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jesse Everett does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Freezing light in mid-air isn’t just the realm of Star Wars, as new research shows. But what do you do with the light once it’s trapped? One option is to use it to develop new forms of computers.Jesse Everett, PhD student at the Australian National University, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/587472016-05-03T20:32:30Z2016-05-03T20:32:30ZSmall and bright: what nanophotonics means for you<figure><img src="https://images.theconversation.com/files/120943/original/image-20160503-19535-16aqe0o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Nanophotonics uses photons to do amazing things.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Twenty fifteen was UNESCO’s <a href="http://www.light2015.org/Home.html">International Year of Light and Light based Technologies</a>. It was a celebration of past milestones in optics and photonics and a look forward into its future. </p>
<p>We celebrated 1,000 years of <a href="http://www.light2015.org/Home/ScienceStories/1000-Years-of-Arabic-Optics.html">Arabic optics</a>, 150 years since <a href="https://en.wikipedia.org/wiki/Maxwell%27s_equations">James Maxwell’s electrodynamics</a>, 100 years since Albert Einstein’s <a href="https://theconversation.com/au/topics/general-relativity">general relativity</a> and 50 years since the invention of optical fibres. This year we celebrate 100 year since <a href="https://www.nyu.edu/pages/linguistics/courses/v610003/shan.html">Claude Shannon</a>, who introduced the theory of information, was born. </p>
<p>Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, followed by theories on light and vision developed by ancient Greek philosophers. </p>
<p>The basic principles of optics are familiar: we wear glasses that rely on refraction to bend light in ways that magnify and sharpen images, use microscopes to see into microscopic worlds and telescopes to look to the stars.</p>
<p>We are probably less familiar with photonics. <a href="https://theconversation.com/au/topics/photonics">Photonics</a> deals with the generation, detection and manipulation of photons, the building blocks of light. The field sprang from the invention of the laser and <a href="https://theconversation.com/au/topics/fiber-optics">fibre optics</a> in the 1960s. </p>
<p>Optical fibres are silica glass wires the size of a human hair that transmit vast amounts of laser-generated information, forming the backbone of today’s internet. </p>
<p>The smartphone also exemplifies the importance of photonics: we use lasers to machine the casing; optics are used in the lithography that manufactures the microelectronic circuits; and the display and the network that connects the phones are both photonics based. </p>
<p>The next milestone will be when the photonics is integrated into the smartphone itself.</p>
<h2>Dawn of nanophotonics</h2>
<p>The 21st century will be the century of photonics and nanotechnology – nanophotonics – which deals the study of the behaviour of light on the nanometre scale, and of the interaction of nanometre-scale objects with light.</p>
<p>It is worth noting that the nanoscale is usually cited as 1–100 nanometres, so a nanometre is a billionth of a metre. In photonics, we are dealing with light waves that have a wavelength around a micron (one thousand nanometres). </p>
<p>However, these light waves interact at around the nanometre scale. So too are the structures that matter when it comes to manipulating this light.</p>
<p>At the University of Sydney we have been creating a new optical processing technology based on nanophotonics. This research is being undertaken by the <a href="http://www.cudos.org.au/">CUDOS ARC Centre of Excellence</a>, which is headquartered in the School of Physics and the <a href="http://sydney.edu.au/nano/hub/index.shtml">Sydney Nanoscience Hub</a> at the University of Sydney with nodes at ANU, RMIT University, Macquarie University, Monash University, Swinburne University and UTS.</p>
<p>At CUDOS we want to take the next step in the evolution of this technology. We want to build a truly photonic chip that will essentially put the entire optical network on to a chip the size of your thumbnail. </p>
<p>By doing this, we can leverage the massive semiconductor industry to harness the processing power of light on a length scale that can be mass produced and integrated into smart devices.</p>
<p>Fortunately silicon – which is the basis of microelectronics – is compatible with photonics. Most silicon chips today, such as the one in your computer and smartphone, use electrons to transmit information and perform computations. The trick has been getting these chips to work with light as well as electrons. </p>
<p>We now can build photonic circuits into the same silicon, although we are not talking about replacing the transistors in conventional chips with optical transistors. Photonics complements and interfaces with electronics.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/53FbwBYrPXI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How nanophotonics can combine with microprocessors.</span></figcaption>
</figure>
<p>Photonic chips, or photonic integrated circuits (PICs), represent a new paradigm in information processing. Over the past decade, CUDOS and other researchers around the world have created PICs for a range of applications spanning communications, computing, defence and security, medicine and sensing. </p>
<p>In communication systems, photonic chips can increase the capacity of our communications networks. In data centres, they are reducing the energy consumption, which matters because every Google search today consumes the energy required to boil a cup of water. </p>
<p>In defence photonic chips can enhance radar technology that helps protect our assets and personnel. And in health, we can reduce the scale and complexity of medical devices that are used to diagnose disease.</p>
<p>Another benefit is in “switching”, which is central to all communications networks. At the new Sydney Nanoscience Hub, we are building nanoscale switching technologies that can switch at the speed of light, thousands of times faster than current switching technology.</p>
<p>We are using state of the art lithography, such as the tools in the Nanoscience Hub’s clean room, to fabricate nanoscale circuits and structures. Lithography literally means printing, but in this context we are printing circuits on silicon wafers with nanometre scale features. </p>
<h2>Bright future</h2>
<p>So what’s next? We need to transform PICs into active devices that sense and interact, analyse, respond to and manipulate their environment. </p>
<p>We are already building photonic spectroscopy techniques into the same silicon chip that performs electronic processing in your smartphone. This will potentially enable your smartphone to perform tasks such as medical diagnosis, including analysing blood or saliva, or sense pollutants in the environment via spectroscopy technologies. </p>
<p>But photonics is not well suited to some of these tasks.</p>
<p>So we need moving parts that can manipulate the microscopic world; we need mechanical actuation at the nanoscale, and we really would prefer a chip with no moving parts. </p>
<p>Our approach is to use sound waves that can be generated on the chip. These are not the traditional sound waves that we hear or use in ultrasound, but ultrahigh frequency sound waves. We refer to them as “phonons”, which are particles of sound, just as photons are particles of light. </p>
<p>We are talking about hypersound, phonons with frequencies from 100 megahertz to tens of gigahertz. We are building a completely new chip that incorporates a photonic circuit for these hypersound phonons. </p>
<p>Harnessing hypersound on a chip enables the manipulation of microscale biological and chemical elements, which means we can mix, sort and select and even create a centrifuge on a chip. This is a laboratory-on-a-chip that can be integrated into the smart phone.</p>
<p>This represents a new paradigm for information processing. The speed of sound is about 100,000 times slower than the speed of light. We can couple information from the light wave to hypersound and store information.</p>
<p>The phonon frequencies coincide with the radio frequencies that are important in next generation mobile communications and radar, which allows us to process these microwave waves via the interaction between optical and phonon waves.</p>
<p>Australia has always punched well above it’s weight in photonics research and commercialisation. We now have the nanoscience and nanotechnology infrastructure and capacity to take the next big step, which is to bring photonics on to the chip where it will transform our lives.</p><img src="https://counter.theconversation.com/content/58747/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Eggleton receives funding from the Australian Research Council, the NSW Department of Trade and Investment and The US Air Force Office of Research. He is on the Council of the Australian Optical Society and the Board of Governors for IEEE Photonics Society.</span></em></p>Nanophotonics deals with photons at the nanometre scale, and it’s set to transform everything from internet speeds to turning your smartphone into a portable science lab.Benjamin J. Eggleton, Professor; ARC Laureate Fellow, Director, ARC Centre of Excellence for Ultrahigh bandwidth Devices for Optical Systems, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/190312013-10-10T09:00:53Z2013-10-10T09:00:53ZThe power of one: single photons illuminate quantum technology<figure><img src="https://images.theconversation.com/files/32810/original/h9spt5qx-1381386106.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">No photon bunches, please.</span> <span class="attribution"><span class="source">derekbruff</span></span></figcaption></figure><p>Quantum mechanics, which aims to describe the nano-scale world around us, has already led to the development of <a href="https://theconversation.com/explainer-quantum-physics-570">many technologies</a> ubiquitous in modern life, including broadband optical fibre communication and smartphone displays. </p>
<p>These devices operate using billions and billions of photons, the smallest indivisible quanta of light - but many powerful quantum effects (such as enabling <a href="https://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">quantum secure communication</a>) can only be harnessed when working with a single photon.</p>
<p>The quantum science community has been waiting for more than a decade for a compact optical chip that delivers exactly one photon at a time at very high rates.</p>
<p>With international and local collaborators, I reported today in <a href="http://www.nature.com/naturecommunications">Nature Communications</a> the ability to combine single photon-generating devices on a single silicon chip, a breakthrough for next generation quantum technologies.</p>
<h2>Photons as qubits</h2>
<p>In 1982, American physicist and Nobel Prize laureate <a href="http://www.feynman.com/">Richard Feynman</a> proposed the idea of building a new type of computer based on the principles of quantum mechanics. </p>
<p>While a regular computer represents information as a <a href="http://en.wikipedia.org/wiki/Bit">bit</a> with a value of either 0 or 1, the quantum equivalent is the <a href="http://en.wikipedia.org/wiki/Qubit">qubit</a>, a quantum particle that has two clear binary states. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=861&fit=crop&dpr=1 600w, https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=861&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=861&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1081&fit=crop&dpr=1 754w, https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1081&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/32797/original/67q2rc52-1381380127.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1081&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Photon™</span></span>
</figcaption>
</figure>
<p>Due to its quantum nature a qubit can be in either state 0, or state 1 or superposition of them both at the same time. </p>
<p>Computations performed using a qubit follow a different set of rules to a regular computer - and this allows certain problems to be solved exponentially faster.</p>
<p>A photon is one example of a quantum particle that can be used as a qubit, and ideally researchers would like to be able to generate photons one by one, as two or more photons in a bunch no longer act as a qubit. </p>
<p>It is easy to generate many photons, but much harder to ensure they come out one by one - photons are gregarious by nature - and a high generation rate is desired, similar to a high central processing unit <a href="http://en.wikipedia.org/wiki/Clock_rate">clock speed</a>. </p>
<p>The creation of single photons has been possible for <a href="http://www.sciencemag.org/content/290/5500/2282.short">some years</a>, but with poor performance and often bulky implementation. We showed that by combining multiple imperfect devices, all on a single silicon chip, we can produce a much higher quality and compact source of single photons, opening a number of new applications.</p>
<h2>Fishing for photons</h2>
<p>The challenge in our research was within the physical mechanism behind photon generation. There is an intrinsic link between the rate of useful single photons creation and how often two or more photons are generated instead: these bunches are unwanted.</p>
<p>Generating higher rates of single photons is thus accompanied by a higher proportion of unwanted additional photons, so we wanted to reduce that to a more favourable ratio.</p>
<p>Think about it in terms of fishing - instead of generating photons, we want to catch fish. An easy option is to send a fisherman out on a boat to cast a net; this will result in a lot of good fish, but also a lot of unwanted garbage. </p>
<p>This is analogous to using a conventional photon source, which generates many photons, but also a lot of unwanted photon bunches. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=237&fit=crop&dpr=1 600w, https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=237&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=237&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=298&fit=crop&dpr=1 754w, https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=298&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/32784/original/dxyr76sr-1381375452.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=298&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A single device for generating single photons (one fisherman) when operating at a high rate (casting a large net) generated unwanted photon bunches. By combining two single photon sources (two fishermen on a boat) on a single silicon chip (the boat), the proportion of ‘garbage’ photon bunches was significantly reduced. In the future we will combine many photon sources on one chip (we want many fishermen!).</span>
<span class="attribution"><span class="source">SevenPixelz</span></span>
</figcaption>
</figure>
<p>Alternatively, we can send two people out with fishing rods. With some luck, they could collectively catch the same number of fish in the same amount of time, but because the method is more selective, the chance of collecting garbage has been vastly reduced. </p>
<p>This is analogous to the work done here: two single photon sources (the fishermen) were combined on a single silicon chip (the boat), with the proportion of “garbage” photon bunches significantly reduced.</p>
<h2>More fishermen</h2>
<p>In the future we will extend this idea and combine many more devices onto a single silicon optical chip. Even though each individual source operates at a lower rate, they can be combined to give much higher rates – you just need more fishermen! </p>
<p>This will allow us to generate a large number of useful single photons, which can act as optical qubits, a fundamental ingredient of complex quantum processors. </p>
<p>The impact of this work opens the potential for more advanced single photon technologies, including secure communication where improved single photon generation directly increases the distance and bit-rate of a quantum secure communication link. </p>
<p>This an active area of research at the Centre for Ultrahigh Bandwidth Devices for Optical Systems (<a href="http://www.cudos.org.au/">CUDOS</a>) within the <a href="http://sydney.edu.au/science/physics/cudos/">University of Sydney</a>. </p>
<p>Still more applications include metrology (the science of measurement), <a href="http://www.nature.com/nphys/journal/v8/n4/full/nphys2258.html">simulation</a> of biological and chemical systems, and - of course - <a href="https://theconversation.com/computing-1-0-1-quantum-information-in-an-atoms-core-13535">quantum computing</a>.</p><img src="https://counter.theconversation.com/content/19031/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matt Collins does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Quantum mechanics, which aims to describe the nano-scale world around us, has already led to the development of many technologies ubiquitous in modern life, including broadband optical fibre communication…Matt Collins, PhD candidate in Physics, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/170602013-08-18T20:20:07Z2013-08-18T20:20:07ZTeleportation just got easier – but not for you, unfortunately<figure><img src="https://images.theconversation.com/files/29318/original/znfhnr3h-1376544108.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Teleportation is still well and truly entrenched in science fiction, unless you're a photon.</span> <span class="attribution"><span class="source">Photon™</span></span></figcaption></figure><p>Thanks to two studies <a href="http://www.nature.com/nature/current_issue.html">published in Nature last Thursday</a>, the chance of successful teleportation has considerably increased. Which is a good thing, right?</p>
<p>Whether or not you’ve ever been on a long-haul flight, you’ve probably fantasised about being able to magically disappear from one place and reappear in another. And a natural question for a physicist is whether there is any way to achieve this in practice.</p>
<p>In fact, something known as “quantum teleportation” became a <a href="http://www.nature.com/nature/journal/v390/n6660/abs/390575a0.html">reality in 1997</a>. This first demonstration was for particles of light (<a href="http://en.wikipedia.org/wiki/Photon">photons</a>). Since then, physicists have also applied teleportation to other very small things, for example <a href="http://physicsworld.com/cws/article/news/2009/jan/22/atoms-teleport-information-over-long-distance">single atoms</a>.</p>
<p>So when can we expect to just teleport ourselves to our chosen destination? You might want to sit down for this. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=816&fit=crop&dpr=1 600w, https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=816&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=816&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1025&fit=crop&dpr=1 754w, https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1025&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/29305/original/cn4zgy95-1376540717.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1025&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption"></span>
<span class="attribution"><span class="source">Wonderlane</span></span>
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<p>The first step to teleporting a person is measuring and recording the position, direction of motion and energy of every particle in the body, which would require more data storage than will ever be available - much, much more. </p>
<p>In fact, a <a href="http://www.wired.com/wired/archive/3.11/krauss_pr.html">conservative estimate</a> would mean you’d need about 10<sup>22</sup> gigabytes (1 followed by 22 zeros) of hard drive space. That’s a stack of hard drives about 20 <a href="http://www.grc.nasa.gov/WWW/k-12/Numbers/Math/Mathematical_Thinking/how_long_is_a_light_year.htm">light-years</a> tall. </p>
<p>Proxima Centauri, the nearest star to Earth other than the sun, is around <a href="http://heasarc.nasa.gov/docs/cosmic/nearest_star_info.html">four light-years away</a>. </p>
<p>Worse, we have no method to even make these measurements, let alone reconstruct a person based on the data. So we can forget about teleporting people.</p>
<h2>Knowing enough - but not too much</h2>
<p>What about something really simple – such as a single particle? How about an atom, or a photon? How can these be teleported?</p>
<p>The problem here was thought to be the <a href="http://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">Heisenberg uncertainty principle</a>, a cornerstone of quantum mechanics that limits what you can know. </p>
<p>It might sound counter-intuitive, but if you try to measure the position of a single atom you will change its velocity. If you find out exactly how fast it is moving, then you won’t know where it is. </p>
<p>The problem is, if you want to teleport a particle, this is precisely the information you want to measure and transmit. </p>
<p>A physicist would call this information the “state” of the particle. If you’re not allowed to measure the complete state of the particle, teleportation looks impossible.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/29317/original/2q74vg7v-1376544051.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
<span class="attribution"><span class="source">jasoneppink</span></span>
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<p>So the key to teleportation is not knowing too much. As long as the measurements that you make do not reveal the position or velocity, then you have a loophole that allows you to circumvent the uncertainty principle. </p>
<p>What if you could disturb the particle before you measure it, so you never know its state, and then subtract off that disturbance at the other end to recreate the original state of the particle? </p>
<p>This was the breakthrough realisation that American physicist <a href="http://goo.gl/fSyvZ">Charles Bennett</a> had in 1993. The key was to disturb the particle you want to teleport in a particular way. You can do this by using a pair of <a href="https://theconversation.com/wind-up-your-clockwork-universe-einstein-if-you-can-524">quantum-entangled particles</a>. </p>
<p>These particles are linked to each other so that if you measure the state of one of the entangled pair, you learn about the state of the other half of the pair. </p>
<h2>Alice and Bob</h2>
<p>In the standard description of teleportation, <a href="http://en.wikipedia.org/wiki/Alice_and_Bob">Alice is teleporting something to Bob</a>. Alice uses one of the entangled particles to measure the state of the input particle. She records what she measures and sends the information to Bob. </p>
<p>Bob can’t tell what the state of the particle was, because the entanglement used in the measurement hides the true nature of the state. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=663&fit=crop&dpr=1 754w, https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=663&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/29306/original/bgy6ytt2-1376540774.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=663&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="attribution"><span class="source">Wikimedia Commons</span></span>
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</figure>
<p>What Bob can do, however, is use the information from Alice to modify the state of the other entangled particle. In this way he can recreate the exact state of the particle Alice originally measured. </p>
<p>This is how quantum teleportation works. Most photon experiments teleport over a metre or so inside a lab, although there has recently been a <a href="http://blog.physicsworld.com/2012/05/22/quantum-teleportation-record-b/">demonstration over 143km</a> in the Canary Islands.</p>
<h2>A sense of security</h2>
<p>It turns out that quantum teleportation is not just a good party trick. The nature of the communication between Alice and Bob in this system is pretty interesting. </p>
<p>The information that Alice measures and sends to Bob cannot be used to recreate the input state without the other entangled particle. That means Eve the eavesdropper can’t spy on Alice’s measurement and get the information for herself. </p>
<p>The entangled pair is unique, so only Bob can recreate the original state. Immediately you have a technique for secure communication. </p>
<p>If you encode information in your particles, measure them with one part of an entangled state and then send the information to Bob, you have cryptography that is made strong by quantum physics. You really can’t crack it by any means, unless you have the other part of the entangled pair.</p>
<h2>Reasons to be cheerful</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=414&fit=crop&dpr=1 600w, https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=414&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=414&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=520&fit=crop&dpr=1 754w, https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=520&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/29322/original/3x7nm39z-1376545696.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=520&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A 128-qubit superconducting adiabatic quantum optimisation processor chip.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>Teleportation has many other uses in <a href="http://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">quantum information systems</a>. </p>
<p>These are <a href="https://theconversation.com/quantum-computers-coming-to-a-store-near-you-16320">proposed methods</a> for building computers and communication networks that use quantum mechanics as a core part of their functionality and have enormous potential to provide secure communications and high-speed computing. </p>
<p>The catch is that any time you want to move quantum information from one place to another in one of these systems, you can’t just measure the information and send it to the next part of the process, since the measurement will destroy the information. Instead, you can teleport it.</p>
<h2>Back to Nature</h2>
<p>The two papers published together in this week’s Nature show something very important. </p>
<p>Until now, teleporting photons of light using the method described above has been probabilistic, because you couldn’t synchronise the arrival of the entangled photons with the arrival of the photon to be measured. </p>
<p>On the odd occasion when the photons aligned, the measurement would only work half the time. That means every time you try and teleport your information it will only work very occasionally - much less than 1% of the time. </p>
<p>If you have a lot of back-to-back-teleporting circuits in your quantum computer or quantum network, the chances of them all working together will become vanishingly small. </p>
<p>These two most recent experiments show deterministic quantum teleportation in two different systems so that the process is no longer probabilistic. Instead it can, in principle, work every time a photon is ready to be teleported. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/29303/original/ybb4rjvx-1376540332.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="attribution"><span class="source">mercurialn</span></span>
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<p><a href="http://www.nature.com/nature/journal/v500/n7462/full/nature12366.html">One of the new studies</a> – by researchers from Japan and Germany – shows how it is possible to teleport photons of light that are in the <a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">infrared spectrum</a>, just below the wavelength visible to the human eye.</p>
<p>The <a href="http://www.nature.com/nature/journal/v500/n7462/full/nature12422.html">other experiment</a> – by researchers in Switzerland and Australia – demonstrates teleportation of microwave photons with a frequencies between 4 and 7 GHz. </p>
<p>Neither system is production-ready, in the sense that they are both just proof of principle experiments. Although the teleportation is no longer probabilistic, it is still not 100% efficient - a 40% chance of success in the case of the infrared system and 25% in the case of the microwave system.</p>
<p>Still, this is a vast improvement on less than 1% that was previously possible with photons. Long-haul flights will continue for some time yet, but the new experiments represent a milestone on the long road to building a functional quantum information system.</p><img src="https://counter.theconversation.com/content/17060/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ben Buchler receives funding from the ARC centre of Excellence for Quantum Computation and Communication technology (CQC2T).</span></em></p>Thanks to two studies published in Nature last Thursday, the chance of successful teleportation has considerably increased. Which is a good thing, right? Whether or not you’ve ever been on a long-haul…Ben Buchler, Research Fellow in Quantum Science, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/106422012-11-12T03:54:15Z2012-11-12T03:54:15Z‘Louder’ light could power a brighter quantum future<figure><img src="https://images.theconversation.com/files/17511/original/4y7c38t8-1352689364.jpg?ixlib=rb-1.1.0&rect=0%2C341%2C1022%2C513&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When you shine a torch into a dusty room, not all the photons reach their destination.</span> <span class="attribution"><span class="source">Simon Greig (xrrr)</span></span></figcaption></figure><p>All of the light we see around us comes in chunks of energy known as <a href="http://en.wikipedia.org/wiki/Photon">photons</a>. As well as making up light, photons can be used to carry and process information and their <a href="https://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">quantum properties</a> make possible new tasks in secure communication, ultra-fast <a href="https://theconversation.com/compute-this-the-quantum-future-is-crystal-clear-6671">quantum computing</a> and more.</p>
<p>To develop these new technologies and the science behind them, we need to learn to manipulate single-photon quantum states in new and powerful ways.</p>
<p>With collaborators at the University of Queensland and the University of Science and Technology of China, my research group at Griffith University has done just that. </p>
<p>We’ve experimentally demonstrated the noiseless amplification of information encoded in a single photon that has been subjected to loss. Our results were <a href="http://arxiv.org/abs/1208.5881">published in Nature Physics</a> on Sunday.</p>
<h2>Loss? Noise? Amplification?</h2>
<p>Amplifiers are ubiquitous in modern technology. They’re used to enlarge singers’ voices at concerts and to boost long-distance data transmission for the internet.</p>
<p>Modern amplifiers pretty much just work, and signals come through crystal clear nearly all of the time. Any imperfections in an amplifier’s output signal are mostly due to technical noise – stuff in the amplifier not working as well as it could.</p>
<p>But through precise engineering design and lots of hard work, this technical noise can be virtually eliminated. That leaves just <a href="http://en.wikipedia.org/wiki/Quantum_noise">quantum noise</a> – uncertainty in the signal due to its fundamentally quantum origin.</p>
<p>This quantum noise is usually so much smaller than the signal being amplified that it can be completely ignored. Unless the signal is a quantum system itself!</p>
<h2>Quantum communications</h2>
<p>In recent years, scientists have been working towards the development of quantum technologies – devices that will use the <a href="https://theconversation.com/explainer-quantum-physics-570">fundamental properties of the quantum world</a> to outperform the best current (or “classical”) technologies.</p>
<p>Among the many approaches being explored is the idea of encoding information into the <a href="http://en.wikipedia.org/wiki/Quantum_state">quantum states</a> – the quantum description of properties such as <a href="http://en.wikipedia.org/wiki/Photon_polarization">polarisation</a> – of photons.</p>
<p>Information transmission and processing with photons has the potential to <a href="https://theconversation.com/explainer-quantum-computation-and-communication-technology-7892">guarantee secure communications</a>, and the ability to calculate solutions to certain problems that <a href="http://motherboard.vice.com/2012/8/21/how-five-times-three-equals-a-hacking-revolution">can’t be practically solved by an ordinary computer</a> – now or ever. </p>
<p>Let’s consider the communication task as an example.</p>
<p>In order to be secure, each quantum bit (or <a href="http://en.wikipedia.org/wiki/Qubit">qubit</a>) of information is typically sent in a single photon. <a href="https://theconversation.com/explainer-heisenbergs-uncertainty-principle-7512">Heisenberg’s Uncertainty Principle</a> means if an eavesdropper tries to measure the information, she disturbs the photon – the quantum version of “you can’t have your cake and eat it too.”</p>
<p>The point is that the intended recipient can detect the intrusion, or proceed with certainty if none exists.</p>
<p>But, crucially, the range of quantum communication is currently limited by the loss of the photons.</p>
<h2>Losing light</h2>
<p>If you shine a flashlight around a dark house, you’ll notice a few things. If you haven’t vacuumed for a while, you might be able to see where the light beam goes by the light that is scattered off dust particles.</p>
<p>And if you shine the flashlight out through a window to see who’s dog is barking, some of the light bounces back off the window. In both cases, not all of the light reaches its intended destination.</p>
<p>Optical communication signals travelling through the atmosphere, or an optical fibre network, also suffer these kinds of loss.</p>
<p>For single photons, loss like this is devastating, because there really isn’t much light to lose! Losing single photons drastically limits the range of quantum-secured communications and other quantum science tasks that require light to travel significant distances. </p>
<h2>Lost or not?</h2>
<p>The funny thing about quantum mechanics is that when a single photon encounters loss, we don’t know whether it’s lost or not until we try to detect it.</p>
<p>It’s just like the famous <a href="https://theconversation.com/teleporting-schrodingers-cats-not-easy-but-its-all-right-miaow-919">Schrodinger’s cat</a> thought experiment in which a hypothetical cat in a box is, because of quantum physics, both alive and dead at the same time.</p>
<p>In fact, quantum physics suggests that it’s the act of looking – opening the lid – that forces a “decision” about the cat’s fate.</p>
<p>Now, if you were a cat-lover confronted with the box containing Schrodinger’s cat, you may wish to try to make it more probable the cat is alive before you open the box. That would mean you’d need to do something to the quantum state of the cat without looking. </p>
<p>And this is exactly what our photon amplifier does. It amplifies the likelihood of the photon being present, without learning any of the information carried in the photon’s quantum state.</p>
<p>The secret to this operation is the idea of quantum teleportation.</p>
<h2>Into the realms of science fiction</h2>
<p>The word “teleportation” brings to mind our favourite science fiction shows, where some kind of matter (often people) are moved over long distances without traversing the space in between. In the quantum version, it’s not matter that’s moved, but information. </p>
<p>The idea in our qubit amplifier scheme is to teleport the information carried by the lossy photon on to another light beam where it’s much more likely a photon is present.</p>
<p>In our experiment, which was based on <a href="http://arxiv.org/abs/1003.0635">an idea</a> by University of Geneva researchers, we took a signal where photons were present just 4% of the times we expected them (the remainder being lost), and amplified it until photons were present 20% of the times expected.</p>
<p>In each case, the quality of the information was preserved to a high degree. In principle, it’s possible to amplify to close to 100% photon presence, but this actually requires improvements in the quality of sources of extra photons used to power the amplifier – a problem on which Australian and international researchers continue to make steady progress.</p>
<h2>Things can only get better</h2>
<p>The laws of quantum physics say that you can’t accurately copy an unknown quantum state, a fact known as the <a href="http://en.wikipedia.org/wiki/No-cloning_theorem">“no cloning theorem”</a>. Because of this kind of idea,
it turns out that the qubit amplifier can’t work every time – sometimes it tries to teleport the information but fails.</p>
<p>But when it succeeds it sends a separate success signal. Thus we know when we can use its output and when we can’t.</p>
<p>It turns out that this is enough to make future versions (with higher amplification) very useful in various quantum communication tasks, as well as for quantum-enhanced measurements, and in the scientific exploration of other strange and useful properties of the quantum world.</p>
<p>Perhaps in the future, qubit amplifiers will be as common in quantum technologies as amplifiers are in classical devices today.</p><img src="https://counter.theconversation.com/content/10642/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Geoff Pryde receives funding from the Australian Research Council, the Defence Science and Technology Organization, and Griffith University. He is a Program Manager in the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology.</span></em></p>All of the light we see around us comes in chunks of energy known as photons. As well as making up light, photons can be used to carry and process information and their quantum properties make possible…Geoff Pryde, Professor in Physics, Griffith UniversityLicensed as Creative Commons – attribution, no derivatives.