tag:theconversation.com,2011:/id/topics/qubits-76705/articlesQubits – The Conversation2024-03-26T17:01:56Ztag:theconversation.com,2011:article/2262572024-03-26T17:01:56Z2024-03-26T17:01:56ZHow long before quantum computers can benefit society? That’s Google’s US$5 million question<figure><img src="https://images.theconversation.com/files/583117/original/file-20240320-26-rmpub2.jpg?ixlib=rb-1.1.0&rect=5%2C0%2C3828%2C2160&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption"></span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/quantum-computer-black-background-3d-render-1571871052">Bartlomiej K. Wroblewski / Shutterstock</a></span></figcaption></figure><p>Google and the XPrize Foundation have launched a competition worth US$5 million (£4 million) to develop <a href="https://blog.google/technology/research/google-gesda-and-xprize-launch-new-competition-in-quantum-applications/">real-world applications for quantum computers</a> that benefit society – by speeding up progress on one of the UN Sustainable Development Goals, for example. The principles of quantum physics suggest quantum computers could perform very fast calculations on particular problems, so this competition may expand the range of applications where they have an advantage over conventional computers.</p>
<p>In our everyday lives, the way nature works can generally be described by what we call <a href="https://en.wikipedia.org/wiki/Classical_physics#:%7E:text=Classical%20physical%20concepts%20are%20often,of%20quantum%20mechanics%20and%20relativity.">classical physics</a>. But nature behaves very differently at tiny quantum scales – below the size of an atom. </p>
<p>The race to harness quantum technology can be viewed as a new industrial revolution, progressing from devices that use the properties of classical physics to those utilising the <a href="https://www.energy.gov/science/doe-explainsquantum-mechanics#:%7E:text=Quantum%20mechanics%20is%20the%20field,%E2%80%9Cwave%2Dparticle%20duality.%E2%80%9D">weird and wonderful properties of quantum mechanics</a>. Scientists have spent decades trying to develop new technologies by harnessing these properties. </p>
<p>Given how often we are told that <a href="https://projects.research-and-innovation.ec.europa.eu/en/horizon-magazine/quantum-technologies">quantum technologies</a> will revolutionise our everyday lives, you may be surprised that we still have to search for practical applications by offering a prize. However, while there are numerous examples of success using quantum properties for enhanced precision in sensing and timing, there has been a surprising lack of progress in the development of quantum computers that outdo their classical predecessors.</p>
<p>The main bottleneck holding up this development is that the software – using <a href="https://www.nature.com/articles/npjqi201523">quantum algorithms</a> –
needs to demonstrate an advantage over computers based on classical physics. This is commonly known as <a href="https://theconversation.com/what-is-quantum-advantage-a-quantum-computing-scientist-explains-an-approaching-milestone-marking-the-arrival-of-extremely-powerful-computers-213306">“quantum advantage”</a>.</p>
<p>A crucial way quantum computing differs from classical computing is in using a property known as <a href="https://spectrum.ieee.org/what-is-quantum-entanglement">“entanglement”</a>. Classical computing <a href="https://web.stanford.edu/class/cs101/bits-bytes.html">uses “bits”</a> to represent information. These bits consist of ones and zeros, and everything a computer does comprises strings of these ones and zeros. But quantum computing allows these bits to be in a <a href="https://azure.microsoft.com/en-gb/resources/cloud-computing-dictionary/what-is-a-qubit">“superposition” of ones and zeros</a>. In other words, it is as if these ones and zeros occur simultaneously in the quantum bit, or qubit.</p>
<p>It is this property which allows computational tasks to be performed all at once. Hence the belief that quantum computing can offer a significant advantage over classical computing, as it is able to perform many computing tasks at the same time. </p>
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<a href="https://theconversation.com/what-is-quantum-advantage-a-quantum-computing-scientist-explains-an-approaching-milestone-marking-the-arrival-of-extremely-powerful-computers-213306">What is quantum advantage? A quantum computing scientist explains an approaching milestone marking the arrival of extremely powerful computers</a>
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<h2>Notable quantum algorithms</h2>
<p>While performing many tasks simultaneously should lead to a performance increase over classical computers, putting this into practice has proven more difficult than theory would suggest. There are actually only a few notable quantum algorithms which can perform their tasks better than those using classical physics.</p>
<figure class="align-center ">
<img alt="Quantum chips - rendering" src="https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=369&fit=crop&dpr=1 600w, https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=369&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=369&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=464&fit=crop&dpr=1 754w, https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=464&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/583127/original/file-20240320-20-fnde2i.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="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/futuristic-cpu-quantum-processor-global-computer-1210158169">Yurchanka Siarhei / Shutterstock</a></span>
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<p>The most notable are the <a href="https://www.st-andrews.ac.uk/physics/quvis/simulations_html5/sims/cryptography-bb84/Quantum_Cryptography.html">BB84 protocol</a>, developed in 1984, and <a href="https://www.nature.com/articles/s41598-021-95973-w">Shor’s algorithm</a>, developed in 1994, both of which use entanglement to outperform classical algorithms on particular tasks. </p>
<p>The BB84 protocol is a cryptographic protocol – a system for ensuring secure, private communication between two or more parties which is considered more secure than comparable classical algorithms.</p>
<p>Shor’s algorithm uses entanglement to demonstrate how current <a href="https://www.rand.org/pubs/commentary/2023/09/when-a-quantum-computer-is-able-to-break-our-encryption.html#:%7E:text=One%20of%20the%20most%20important,secure%20internet%20traffic%20against%20interception.">classical encryption protocols can be broken</a>, because they are based on the factorisation of very large numbers. <a href="https://ieeexplore.ieee.org/document/365700">There is also evidence</a> that it can perform certain calculations faster than similar algorithms designed for conventional computers. </p>
<p>Despite the superiority of these two algorithms over conventional ones, few advantageous quantum algorithms have followed. However, researchers have not given up trying to develop them. Currently, there are a couple of main directions in research.</p>
<h2>Potential quantum benefits</h2>
<p>The first is to use quantum mechanics to assist in what are called <a href="https://arxiv.org/abs/2312.02279">large-scale optimisation tasks</a>. Optimisation – finding the best or most effective way to solve a particular task – is vital in everyday life, from ensuring traffic flow runs effectively, to managing operational procedures in factory pipelines, to streaming services deciding what to recommend to each user. It seems clear that quantum computers could help with these problems.</p>
<p>If we could reduce the computational time required to perform the optimisation, it could save energy, reducing the carbon footprint of the many computers currently performing these tasks around the world and the data centres supporting them.</p>
<p>Another development that could offer wide-reaching benefits is to use quantum computation to simulate systems, such as combinations of atoms, that behave according to quantum mechanics. Understanding and predicting how quantum systems work in practice could, for example, lead to better drug design and medical treatments. </p>
<p>Quantum systems could also lead to improved electronic devices. As computer chips get smaller, quantum effects take hold, potentially reducing the devices’s performance. A better fundamental understanding of quantum mechanics could help avoid this.</p>
<p>While there has been significant investment in building quantum computers, there has been less focus on ensuring they will directly benefit the public. However, that now appears to be changing.</p>
<p>Whether we will all have quantum computers in our homes within the next 20 years remains doubtful. But, given the current financial commitment to making quantum computation a practical reality, it seems that society is finally in a better position to make use of them. What precise form will this take? There’s US$5 million dollars on the line to find out.</p><img src="https://counter.theconversation.com/content/226257/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adam Lowe 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 computing has huge promise from a technical perspective, but the practical benefits are less clear.Adam Lowe, Lecturer, School of Computer Science and Digital Technologies, Aston UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2133062023-11-17T13:29:43Z2023-11-17T13:29:43ZWhat is quantum advantage? A quantum computing scientist explains an approaching milestone marking the arrival of extremely powerful computers<figure><img src="https://images.theconversation.com/files/559476/original/file-20231114-21-dv3rca.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5731%2C3829&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">IBM's quantum computer got President Joe Biden's attention.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/president-joe-biden-looks-at-quantum-computer-as-he-tours-news-photo/1243772280">Mandel Ngan/AFP via Getty Images</a></span></figcaption></figure><p>Quantum advantage is the milestone the field of quantum computing is fervently working toward, where a quantum computer can solve problems that are beyond the reach of the most powerful non-quantum, or classical, computers. </p>
<p>Quantum refers to the scale of atoms and molecules where the laws of physics as we experience them break down and a different, counterintuitive set of laws apply. Quantum computers take advantage of these strange behaviors to solve problems.</p>
<p>There are some types of problems that are <a href="https://theconversation.com/limits-to-computing-a-computer-scientist-explains-why-even-in-the-age-of-ai-some-problems-are-just-too-difficult-191930">impractical for classical computers to solve</a>, such as cracking state-of-the-art encryption algorithms. Research in recent decades has shown that quantum computers have the potential to solve some of these problems. If a quantum computer can be built that actually does solve one of these problems, it will have demonstrated quantum advantage.</p>
<p>I am <a href="https://scholar.google.com/citations?user=2J2t64gAAAAJ&hl=en">a physicist</a> who studies quantum information processing and the control of quantum systems. I believe that this frontier of scientific and technological innovation not only promises groundbreaking advances in computation but also represents a broader surge in quantum technology, including significant advancements in quantum cryptography and quantum sensing.</p>
<h2>The source of quantum computing’s power</h2>
<p>Central to quantum computing is the quantum bit, or <a href="https://quantumatlas.umd.edu/entry/qubit/">qubit</a>. Unlike classical bits, which can only be in states of 0 or 1, a qubit can be in any state that is some combination of 0 and 1. This state of neither just 1 or just 0 is known as a <a href="https://quantumatlas.umd.edu/entry/superposition/">quantum superposition</a>. With every additional qubit, the number of states that can be represented by the qubits doubles. </p>
<p>This property is often mistaken for the source of the power of quantum computing. Instead, it comes down to an intricate interplay of superposition, <a href="https://encyclopedia2.thefreedictionary.com/Quantum+Interference">interference</a> and <a href="https://theconversation.com/nobel-winning-quantum-weirdness-undergirds-an-emerging-high-tech-industry-promising-better-ways-of-encrypting-communications-and-imaging-your-body-191929">entanglement</a>.</p>
<p>Interference involves manipulating qubits so that their states combine constructively during computations to amplify correct solutions and destructively to suppress the wrong answers. Constructive interference is what happens when the peaks of two waves – like sound waves or ocean waves – combine to create a higher peak. Destructive interference is what happens when a wave peak and a wave trough combine and cancel each other out. Quantum algorithms, which are few and difficult to devise, set up a sequence of interference patterns that yield the correct answer to a problem.</p>
<p>Entanglement establishes a uniquely quantum correlation between qubits: The state of one cannot be described independently of the others, no matter how far apart the qubits are. This is what Albert Einstein famously dismissed as “spooky action at a distance.” Entanglement’s collective behavior, orchestrated through a quantum computer, enables computational speed-ups that are beyond the reach of classical computers.</p>
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<figcaption><span class="caption">The ones and zeros – and everything in between – of quantum computing.</span></figcaption>
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<h2>Applications of quantum computing</h2>
<p>Quantum computing has a range of potential uses where it can outperform classical computers. In cryptography, quantum computers pose both an opportunity and a challenge. Most famously, they have the <a href="https://theconversation.com/is-quantum-computing-a-cybersecurity-threat-107411">potential to decipher current encryption algorithms</a>, such as the widely used <a href="https://www.britannica.com/topic/RSA-encryption">RSA scheme</a>. </p>
<p>One consequence of this is that today’s encryption protocols need to be reengineered to be resistant to future quantum attacks. This recognition has led to the burgeoning field of <a href="https://www.nist.gov/programs-projects/post-quantum-cryptography">post-quantum cryptography</a>. After a long process, the National Institute of Standards and Technology recently selected four quantum-resistant algorithms and has begun the process of readying them so that organizations around the world can use them in their encryption technology.</p>
<p>In addition, quantum computing can dramatically speed up quantum simulation: the ability to predict the outcome of experiments operating in the quantum realm. Famed physicist Richard Feynman <a href="https://doi.org/10.1007/BF02650179">envisioned this possibility</a> more than 40 years ago. Quantum simulation offers the potential for considerable advancements in chemistry and materials science, aiding in areas such as the intricate modeling of molecular structures for drug discovery and enabling the discovery or creation of materials with novel properties. </p>
<p>Another use of quantum information technology is <a href="https://doi.org/10.1103/RevModPhys.89.035002">quantum sensing</a>: detecting and measuring physical properties like electromagnetic energy, gravity, pressure and temperature with greater sensitivity and precision than non-quantum instruments. Quantum sensing has myriad applications in fields such as <a href="https://www.azoquantum.com/Article.aspx?ArticleID=444">environmental monitoring</a>, <a href="https://doi.org/10.1038/s41586-021-04315-3">geological exploration</a>, <a href="https://doi.org/10.1038/s42254-023-00558-3">medical imaging</a> and <a href="https://www.defenseone.com/ideas/2022/06/quantum-sensorsunlike-quantum-computersare-already-here/368634/">surveillance</a>.</p>
<p>Initiatives such as the development of a quantum internet that interconnects quantum computers are crucial steps toward bridging the quantum and classical computing worlds. This network could be secured using quantum cryptographic protocols such as quantum key distribution, which enables ultra-secure communication channels that are protected against computational attacks – including those using quantum computers.</p>
<p>Despite a growing application suite for quantum computing, developing new algorithms that make full use of the quantum advantage – in particular <a href="https://journals.aps.org/prxquantum/pdf/10.1103/PRXQuantum.3.030101">in machine learning</a> – remains a critical area of ongoing research.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a metal apparatus with green laser light in the background" src="https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/559489/original/file-20231115-29-uo273g.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>
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<span class="caption">A prototype quantum sensor developed by MIT researchers can detect any frequency of electromagnetic waves.</span>
<span class="attribution"><a class="source" href="https://news.mit.edu/2022/quantum-sensor-frequency-0621">Guoqing Wang</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
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<h2>Staying coherent and overcoming errors</h2>
<p>The quantum computing field faces significant hurdles in hardware and software development. Quantum computers are highly sensitive to any unintentional interactions with their environments. This leads to the phenomenon of decoherence, where qubits rapidly degrade to the 0 or 1 states of classical bits. </p>
<p>Building large-scale quantum computing systems capable of delivering on the promise of quantum speed-ups requires overcoming decoherence. The key is developing effective methods of suppressing and correcting quantum errors, <a href="http://www.cambridge.org/9780521897877">an area my own research is focused on</a>.</p>
<p>In navigating these challenges, numerous quantum hardware and software startups have emerged alongside well-established technology industry players like Google and IBM. This industry interest, combined with significant investment from governments worldwide, underscores a collective recognition of quantum technology’s transformative potential. These initiatives foster a rich ecosystem where academia and industry collaborate, accelerating progress in the field.</p>
<h2>Quantum advantage coming into view</h2>
<p>Quantum computing may one day be as disruptive as the arrival of <a href="https://memberservices.theconversation.com/newsletters/?nl=ai">generative AI</a>. Currently, the development of quantum computing technology is at a crucial juncture. On the one hand, the field has already shown early signs of having achieved a narrowly specialized quantum advantage. <a href="https://www.nature.com/articles/s41586-019-1666-5">Researchers at Google</a> and later a <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.180501">team of researchers in China</a> demonstrated quantum advantage <a href="https://doi.org/10.1038/s41534-023-00703-x">for generating a list of random numbers</a> with certain properties. My research team demonstrated a quantum speed-up <a href="https://doi.org/10.1103/PhysRevLett.130.210602">for a random number guessing game</a>.</p>
<p>On the other hand, there is a tangible risk of entering a “quantum winter,” a period of reduced investment if practical results fail to materialize in the near term.</p>
<p>While the technology industry is working to deliver quantum advantage in products and services in the near term, academic research remains focused on investigating the fundamental principles underpinning this new science and technology. This ongoing basic research, fueled by enthusiastic cadres of new and bright students of the type I encounter almost every day, ensures that the field will continue to progress.</p><img src="https://counter.theconversation.com/content/213306/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Daniel Lidar receives funding from the NSF, DARPA, ARO, and DOE.</span></em></p>Several companies have made quantum computers, but these early models have yet to demonstrate quantum advantage: the ability to outstrip ordinary supercomputers.Daniel Lidar, Professor of Electrical Engineering, Chemistry, and Physics & Astronomy, University of Southern CaliforniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1960652023-01-12T08:22:48Z2023-01-12T08:22:48ZQuantum computers threaten our whole cybersecurity infrastructure: here’s how scientists can bulletproof it<figure><img src="https://images.theconversation.com/files/502119/original/file-20221220-20-oerjes.jpg?ixlib=rb-1.1.0&rect=105%2C19%2C3089%2C1978&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Against quantum cyber attacks, one can use smarter softwares, or encrypt communications differently in terms of hardware.</span> <span class="attribution"><a class="source" href="https://unsplash.com/fr/photos/wGICoyAhEs4">Salvatore Andrea Santacroce/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><a href="https://www.nature.com/articles/s41586-021-03928-y">Thirteen</a>, <a href="https://www.nature.com/articles/s41586-019-1666-5">53</a> and <a href="https://www.newscientist.com/article/2346074-ibm-unveils-worlds-largest-quantum-computer-at-433-qubits/">433</a>. That’s the size of <em>quantum computers</em> in terms of <a href="https://learn.microsoft.com/en-us/azure/quantum/concepts-the-qubit">quantum bits</a>, or qubits, which has significantly grown in the last years due to important public and private investments and initiatives. Obviously, it is not only a mere question of quantity: the quality of the prepared qubits is as important as their number for a quantum computer to beat our existing classical computers, that is, to attain what’s called the “quantum advantage”. Yet it is conceivable that soon quantum-computing devices delivering such an advantage will be available. How would this affect our daily lives?</p>
<p>Making predictions is never easy, but it is agreed that <em>cryptography</em> will be altered by the advent of quantum computers. It is an almost trivial statement that privacy is a key issue in our information society: every day, immense amounts of confidential data are exchanged through the Internet. The security of these transactions is crucial and mostly depends on a single concept: complexity or, more precisely, computational complexity. Confidential information remains secret because any eavesdropper wanting to read it needs to solve an extremely complex mathematical problem.</p>
<p>In fact, the problems used for cryptography are so complex for our present algorithms and computers that the information exchange remains secure for any practical purposes – solving the problem and then hacking the protocol would take a ridiculous number of years. The most paradigmatic example of this approach is the <a href="https://en.wikipedia.org/wiki/RSA_(cryptosystem)">RSA protocol</a> (for its inventors Ron Rivest, Adi Shamir and Leonard Adleman), which today secures our information transmissions. </p>
<p>The security of the RSA protocol is based on the fact that we don’t yet have any efficient algorithm to <a href="https://medium.com/coinmonks/integer-factorization-defining-the-limits-of-rsa-cracking-71fc0675bc0e">factorise large numbers</a> – given a large number, the goal is to find two numbers whose product is equal to the initial number. For example, if the initial number is 6, the solution is 2 and 3, as 6=2x3. Cryptographic protocols are constructed in such a way that the enemy, to decrypt the message, needs to factorise a <em>very</em> large number (not 6!), which is at present impossible to do.</p>
<p>If computing devices are built for that would allow current cryptography methods to be easily cracked, our current privacy paradigm needs to be rethought. This will be the case for <a href="https://theconversation.com/google-claims-to-have-invented-a-quantum-computer-but-ibm-begs-to-differ-127309">quantum computers</a> (once an operational quantum computer exists, that is): they should be able to break RSA because there is a <a href="https://ieeexplore.ieee.org/abstract/document/365700">quantum algorithm for efficient factorisation</a>. While classical computers may need the age of the universe to such a problem, <em>ideal</em> quantum computers should be able to do it in a <a href="https://arxiv.org/pdf/1905.09749.pdf">few hours</a> or maybe even minutes. </p>
<p>This is why cryptographers are developing solutions to replace RSA and attain <em>quantum-safe security</em>, that is, cryptographic protocols that are secure against an enemy who has access to a quantum computer. To do so, there exist two main approaches: <em>post-quantum cryptography</em> and <em>quantum key distribution</em>.</p>
<h2>How to encrypt information in a world equipped with quantum computers</h2>
<p>Post-quantum cryptography maintains the security paradigm based on complexity. One should look for mathematical problems that remain difficult for quantum computers and use them to construct cryptographic protocols, the idea again being that an enemy can hack them only after a ridiculously large amount of time. Researchers are working hard to develop algorithms for post-quantum cryptography. In fact, the National Institute of Standards and Technology (NIST) initiated a process to <a href="https://csrc.nist.gov/projects/post-quantum-cryptography/selected-algorithms-2022">solicit and evaluate these algorithms</a> and the chosen candidates were announced in July 2022.</p>
<p>Post-quantum cryptography presents a very strong advantage: it is based on software. It is therefore cheap and, more importantly, its integration with existing infrastructures is straightforward, as one only needs to replace the previous protocol, say RSA, by the new one.</p>
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<p>But post-quantum cryptography also has a clear risk: our confidence on the “hardness” of the chosen algorithms against quantum computers is limited. Here it is important to recall that, strictly speaking, none of the cryptographic protocols based on complexity are proven to be secure. In other words, there is no proof that they cannot be solved efficiently on a classical or quantum computer.</p>
<p>This is the case for factoring: one can’t rule out the discovery of an efficient algorithm for factorisation that would enable a classic computer to break down RSA, no quantum computer required. While unlikely, such a possibility cannot be excluded. In the case of the new algorithms, the evidence of their complexity is much more limited, as they have not yet been intensively tested against smart researchers, much less quantum computers. Indeed, a quantum-safe algorithm proposed in the NIST initiative was later <a href="https://thequantuminsider.com/2022/08/05/nist-approved-post-quantum-safe-algorithm-cracked-in-an-hour-on-a-pc/">cracked in an hour on a standard PC</a>.</p>
<h2>Exploit the laws of quantum physics to secure communications</h2>
<p>The second approach for quantum-safe security is <a href="https://www.ssi.gouv.fr/en/publication/should-quantum-key-distribution-be-used-for-secure-communications/"><em>quantum key distribution</em></a>. Here, the security of the protocols is no longer based on complexity considerations, but on the laws of quantum physics. We therefore speak of quantum <em>physical security</em>.</p>
<p>Without entering into the details, a secret key is distributed using qubits and the protocol’s security follows from the <a href="https://en.wikipedia.org/wiki/Uncertainty_principle">Heisenberg uncertainty principle</a>, which implies that any intervention by the eavesdropper is detected because modifies the state of these qubits. The main advantage of quantum key distribution is that it is based on quantum phenomena that have been verified in many experimental labs.</p>
<p>The main problem for its adoption is that it requires new (quantum) hardware. It is therefore expensive and its integration with existing infrastructures is not easy. Yet important initiatives are taking place for the <a href="https://digital-strategy.ec.europa.eu/en/policies/european-quantum-communication-infrastructure-euroqci">deployment of quantum key distribution at a European scale</a>.</p>
<p>Which approach to take? This question is often presented as an either-or choice and even in this article, you may have given this impression too. However, our vision is that the right way to go is to look for the combination of post-quantum and quantum key distribution. The latter has shown us that quantum physics provides us with new tools and recipes to truly safeguard our secrets. If the two approaches are combined, hackers will have a <em>much</em> more difficult time, as they will have to face both complex computational problems and quantum phenomena.</p>
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<img alt="" src="https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=158&fit=crop&dpr=1 600w, https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=158&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=158&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=198&fit=crop&dpr=1 754w, https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=198&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/310261/original/file-20200115-134768-1tax26b.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=198&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em>Created in 2007 to help accelerate and share scientific knowledge on key societal issues, the AXA Research Fund has supported nearly 700 projects around the world conducted by researchers in 38 countries. To learn more, visit the site of the AXA Research Fund or follow on Twitter @AXAResearchFund.</em></p><img src="https://counter.theconversation.com/content/196065/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Antonio Acín is ICREA Professor at the ICFO-The Institute of Photonic Sciences. Il received funding from the AXA Research Fund, the European Union and the Spanish and Catalan gouvernments.</span></em></p>To protect against future quantum cyber attacks, two technological paths are being explored. Decryption.Antonio Acín, Professor and group leader, Instituto de Ciencias Fotónicas (ICFO)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1919892022-10-25T13:03:37Z2022-10-25T13:03:37ZCould energy efficiency be quantum computers’ greatest strength yet?<figure><img src="https://images.theconversation.com/files/490845/original/file-20221020-26-a4hkfz.jpg?ixlib=rb-1.1.0&rect=0%2C50%2C5568%2C3650&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The energy consumption of large computers is very high – so what about future quantum computers?</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/VT4rx775FT4">maximalfocus/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><a href="https://www.youtube.com/watch?v=bayTbt_8aNc">Quantum computers</a> have attracted considerable interest of late for their potential to crack problems in a few hours where <a href="https://hal.inria.fr/hal-00925622/document">they might take the age of the universe</a> (i.e., tens of billions of years) on the best supercomputers. Their <a href="https://theconversation.com/retour-sur-les-technologies-quantiques-sont-elles-pretes-a-entrer-dans-nos-vies-159740">real-life applications</a> are manifold and range from drugs and materials design to solving complex optimisation problems. They are therefore primarily intended for scientific and industrial research.</p>
<p>Traditionally, <a href="https://theconversation.com/cartes-bleues-et-securite-des-echanges-vers-une-cryptographie-post-quantique-178478">“quantum supremacy”</a> is sought from the point of view of raw computing power: we want to calculate (much) faster.</p>
<p>However, the question of its energy consumption could also now warrant research, with current supercomputers sometimes consuming <a href="https://www.la-croix.com/France/Meta-supercalculateurs-quoi-faire-2022-01-25-1201196837">as much electricity as a small town</a> (which could in fact <a href="http://www.cai2.sk/ojs/index.php/cai/article/view/1960">limit the increase in their computing power</a>). Information technologies, at their end, accounted for <a href="https://www.nature.com/articles/s43246-020-0022-5">11% of global electricity consumption</a> in 2020.</p>
<h2>Why focus on the energy consumption of quantum computers?</h2>
<p>Since a quantum computer can solve problems in a few hours where a supercomputer might take several tens of billions of years, it is natural to expect it will consume much less energy. However, manufacturing such powerful quantum computers will require that we solve many scientific and technological challenges, potentially over one to several decades of research.</p>
<p>A more modest goal would be to create less powerful quantum computers, capable of solving computations in a time relatively comparable to supercomputers, but using much less energy.</p>
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<img alt="" src="https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491064/original/file-20221021-20-ppcrlh.jpeg?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="caption">Google, Amazon, Microsoft and IBM are some of the tech giants to have taken an interest in quantum computing.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/ibm_research_zurich/40645906341">Graham Carlow</a></span>
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<p>This potential energy benefit of quantum computing has already been discussed. Google’s <a href="https://www.nature.com/articles/s41586-019-1666-5">Sycamore quantum processor</a> consumes 26 kilowatts of electrical power, far less than a supercomputer, and runs a test quantum algorithm in seconds. Following the experiment, scientists put forward classical algorithms to simulate the quantum algorithm. The first proposals for classical algorithms required <a href="https://www.ibm.com/blogs/research/2019/10/on-quantum-supremacy/">much more energy</a> – which seemed to demonstrate the energy advantage of quantum computing, but they were soon followed by <a href="https://journals.aps.org/prx/abstract/10.1103/PhysRevX.10.041038">other proposals</a>, which were much more energy efficient.</p>
<p>The question of the energy advantage is therefore still open to question and is an open research topic, especially since the quantum algorithm performed by Sycamore has no identified “useful” application to date.</p>
<h2>Superposition: the fragile phenomenon at the heart of quantum computing</h2>
<p>To know whether quantum computers can be expected to provide an energy advantage, it is necessary to understand the fundamental laws according to which they operate.</p>
<p>Quantum computers manipulate physical systems called <a href="https://azure.microsoft.com/en-us/resources/cloud-computing-dictionary/what-is-a-qubit/">qubits</a> (for <em>quantum bits</em>) to perform a calculation. A qubit can take two values: 0 (the “ground state”, of minimum energy) and 1 (the “excited state”, of maximum energy). It can also occupy a “superposition” of 0 and 1. <a href="https://press.princeton.edu/books/hardcover/9780691183527/philosophy-of-physics">How we interpret superpositions is still the subject of heated philosophical debates</a>, but, to put it simply, it means that the qubit can be “both” in state 0 and state 1 with certain associated <a href="https://www.feynmanlectures.caltech.edu/III_03.html">“probability amplitudes”</a>.</p>
<p>Thanks to these probabilities, we can <a href="https://www.nature.com/articles/nature13460">greatly simplify</a> the principle of the quantum computer by saying that it implements algorithms that perform calculations on several numbers “at once” (in this case 0 and 1 at the same time). This advantage becomes clear when the number of qubits is increased: 300 qubits in superpositions are capable of representing 2 to the power of 300 states at the same time. As an example, <a href="https://www.youtube.com/watch?v=4cwtlmTfNYA">this is approximately the number of atoms in the observable universe</a> – so representing so many states <em>at once</em> on a supercomputer is completely unrealistic.</p>
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<img alt="A man stands by a quantum computer in California" src="https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=387&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=387&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=387&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491014/original/file-20221021-12-dnas7u.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&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">Erik Lucero, lead engineer of Google Quantum AI, stands beside a quantum computer in Goleta, California in September.</span>
<span class="attribution"><a class="source" href="https://news.afp.com/#/c/main/search/photos?id=newsml.afp.com.20220922T015329Z.doc-32jv4yv&type=photo">Frederic Brown/AFP</a></span>
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<p>However, the foundations of quantum theory tell us that if the values of these probability amplitudes are “measured” by another physical system, then the superposition is destroyed: the qubit relaxes to the value of 1 or 0, thus introducing an error into the calculation.</p>
<p>One concrete example of such a destruction is when the qubit absorbs a photon (a particle of light that is a small packet of energy). If this is the case, it is because it was not in its maximum energy state (since it can absorb energy, that of the photon). The photon, and therefore through it the “environment” of the qubit has therefore indirectly “found” the value of the amplitudes, which destroys the superposition. This is called <a href="https://arxiv.org/abs/quant-ph/0306072">“decoherence”</a>.</p>
<p>[<em>Nearly 80,000 readers look to The Conversation France’s newsletter for expert insights into the world’s most pressing issues</em>. <a href="https://theconversation.com/fr/newsletters/la-newsletter-quotidienne-5?utm_source=inline-70ksignup">Sign up now</a>]</p>
<p>Generally speaking, the challenge is to ensure that the qubits are sufficiently isolated to avoid any information leakage: we can’t allow a photon or another particle to disturb our qubit. This is a challenge because the qubits must also be controllable: they cannot be completely isolated.</p>
<p>This lack of protection is the main source of error in qubit-based calculations. For example, one of the most mature qubit technologies runs into an <a href="https://arxiv.org/abs/1905.13641">error every 1,000 operations</a>. When you consider that <a href="https://arxiv.org/abs/1905.09749">it takes 10¹³ operations</a> for a typical quantum algorithm, you can see that this is far too many.</p>
<h2>Preserving superpositions has an energy cost</h2>
<p>The energy cost of computing a quantum computer will mostly come from this need for “protection of the quantum data”. For example, it is often necessary to set the qubit environment close to absolute zero (-273°C) to ensure that no photons populate this environment, avoiding the problem mentioned above. This is a very energy-intensive process.</p>
<p>Some other techniques, such as <a href="https://www.pourlascience.fr/sd/technologie/les-codes-correcteurs-d-erreurs-quantiques-23810.php">quantum error correction</a>, also preserve quantum information, and can improve the fidelity of operations. However, in addition to the challenges they raise, these techniques also incur a very high energy cost because they involve error detection algorithms, or additional qubits for error detection, etc.</p>
<p>In short, the more accurate we want an operation performed on a qubit to be, the more it will have to be protected, and the more energy we will have to spend for that. There is a very strong link between “error rate” and “energy” in quantum computing. Understanding this link precisely may then allow the design of a very energy efficient computer.</p>
<h2>Is an energy quantum advantage possible?</h2>
<p>Some theoretical studies have been able to calculate the energy cost necessary for the realisation of quantum computers, but in a <a href="https://arxiv.org/abs/2103.16726">non-optimised regime</a>, notably not exploiting the link between error rate and energy, and often with a <a href="https://arxiv.org/abs/2205.12092">simplified model</a> of the computer.</p>
<p>Exploiting this link can lead to powerful optimisations <a href="https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.2.040335">reducing the energy cost of algorithms</a>. In practice, <a href="https://tel.archives-ouvertes.fr/tel-03579666">this requires an interdisciplinary approach</a> including the understanding of the fundamental phenomena inducing decoherence, the modelling of quantum error correction algorithms and codes as well as the whole “engineering” part necessary to control the qubits. One can then calculate the minimal energy cost needed to solve different problems, while aiming at an error probability for the algorithm considered as “acceptable”.</p>
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<img alt="A disk from a quantum computing system" src="https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/491081/original/file-20221021-13-3lhsfi.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&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">A wafer of a D-Wave quantum computing system.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/jurvetson/39188583425">Creative Commons Attribution</a></span>
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<p>As <a href="https://arxiv.org/abs/2209.05469">we have seen</a>, for qubits of excellent quality (i.e., of a quality that is still out of reach in practice today), there are tasks for which the quantum computer could spend one hundred times less energy than the best current supercomputers for a comparable calculation time (comparable in the sense that both would be able to solve the task in a reasonable time). This energy gain of a factor of 100 is also indicative: one could imagine saving more energy by carrying out additional optimisations.</p>
<p>This is because a quantum computer computes using fundamentally different processes to a classical computer: the former manipulates qubits and the latter bits. Thus, for the same task and even for the same computing time, the number of operations can be drastically different. Moreover, an operation performed in a quantum computer will involve physical processes that are radically different from implemented on a supercomputer. These two remarks taken together imply that, conceptually, even at equal computation time, even if a quantum logic operation consumes more energy than a classical logic operation, the smaller number of quantum logic operations may mean that the quantum computer will ultimately be much more energy-efficient.</p>
<p>Of course, this example comes from theoretical calculations, based on sometimes highly optimistic assumptions. However, it does seem to indicate that one of the primary advantages of quantum computing <a href="https://quantum-energy-initiative.org/">may well be energetic before it is computational</a>.</p><img src="https://counter.theconversation.com/content/191989/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marco Fellous-Asiani 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>Recent suggests quantum computers could solve problems with breathtaking speed by comparison to current supermodels.Marco Fellous-Asiani, Post-doctorant en information quantique au Centre of New Technologies, University of WarsawLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1659562021-08-13T22:17:02Z2021-08-13T22:17:02ZHow a simple crystal could help pave the way to full-scale quantum computing<figure><img src="https://images.theconversation.com/files/415984/original/file-20210813-27-1uv81jl.jpeg?ixlib=rb-1.1.0&rect=0%2C25%2C3360%2C2208&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Serwan Asaad/UNSW</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Vaccine and drug development, artificial intelligence, transport and logistics, climate science — these are all areas that stand to be transformed by the development of a full-scale quantum computer. And there has been <a href="https://www.wsj.com/articles/psiquantum-raises-450-million-to-build-its-quantum-computer-11627387321">explosive growth</a> in quantum computing <a href="https://www.forbes.com/sites/moorinsights/2021/03/23/ionq-takes-quantum-computing-public-with-a-2-billion-deal/?sh=271072285d06">investment</a> over the past decade.</p>
<p>Yet current quantum processors are relatively small in scale, with fewer than 100 <em>qubits</em> — the basic building blocks of a quantum computer. Bits are the smallest unit of information in computing, and the term qubits stems from “quantum bits”.</p>
<p>While early quantum processors have been crucial for demonstrating the potential of quantum computing, realising globally significant applications will likely require processors with <a href="https://www.pnas.org/content/114/29/7555">upwards of a million qubits</a>.</p>
<p>Our new research tackles a core problem at the heart of scaling up quantum computers: how do we go from controlling just a few qubits, to controlling millions? In research <a href="https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abg9158">published today</a> in Science Advances, we reveal a new technology that may offer a solution.</p>
<h2>What exactly is a quantum computer?</h2>
<p>Quantum computers use qubits to hold and process quantum information. Unlike the bits of information in classical computers, qubits make use of the quantum properties of nature, known as “superposition” and “entanglement”, to perform some calculations much faster than their classical counterparts.</p>
<p>Unlike a classical bit, which is represented by either 0 or 1, a qubit can exist in <em>two</em> states (that is, 0 and 1) at the same time. This is what we refer to as a superposition state.</p>
<p>Demonstrations by <a href="https://www.nature.com/articles/s41586-019-1666-5">Google</a> and <a href="https://science.sciencemag.org/content/370/6523/1460">others</a> have shown even current, early-stage quantum computers can outperform the most powerful supercomputers on the planet for a highly specialised (albeit not particularly useful) task — reaching a milestone we call quantum supremacy.</p>
<p>Google’s quantum computer, built from superconducting electrical circuits, had just 53 qubits and was cooled to a temperature close to -273°C in a high-tech refrigerator. This extreme temperature is needed to remove heat, which can introduce errors to the fragile qubits. While such demonstrations are important, the challenge now is to build quantum processors with many more qubits.</p>
<p>Major efforts are underway at UNSW Sydney to make quantum computers from the same material used in everyday computer chips: silicon. A conventional silicon chip is thumbnail-sized and packs in several billion bits, so the prospect of using this technology to build a quantum computer is compelling.</p>
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Read more:
<a href="https://theconversation.com/quantum-computers-could-arrive-sooner-if-we-build-them-with-traditional-silicon-technology-123115">Quantum computers could arrive sooner if we build them with traditional silicon technology</a>
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<h2>The control problem</h2>
<p>In silicon quantum processors, information is stored in individual electrons, which are trapped beneath small electrodes at the chip’s surface. Specifically, the qubit is coded into the electron’s <a href="https://en.wikipedia.org/wiki/Spin_(physics)">spin</a>. It can be pictured as a small compass inside the electron. The needle of the compass can point north or south, which represents the 0 and 1 states. </p>
<p>To set a qubit in a superposition state (both 0 <em>and</em> 1), an operation that occurs in all quantum computations, a control signal must be directed to the desired qubit. For qubits in silicon, this control signal is in the form of a microwave field, much like the ones used to carry phone calls over a 5G network. The microwaves interact with the electron and cause its spin (compass needle) to rotate.</p>
<p>Currently, each qubit requires its own microwave control field. It is delivered to the quantum chip through a cable running from room temperature down to the bottom of the refrigerator at close to -273°C. Each cable brings heat with it, which must be removed before it reaches the quantum processor.</p>
<p>At around 50 qubits, which is state-of-the-art today, this is difficult but manageable. Current refrigerator technology can cope with the cable heat load. However, it represents a huge hurdle if we’re to use systems with a million qubits or more.</p>
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<h2>The solution is ‘global’ control</h2>
<p>An elegant solution to the challenge of how to deliver control signals to millions of spin qubits was <a href="https://www.nature.com/articles/30156">proposed in the late 1990s</a>. The idea of “global control” was simple: broadcast a single microwave control field across the entire quantum processor. </p>
<p>Voltage pulses can be applied locally to qubit electrodes to make the individual qubits interact with the global field (and produce superposition states).</p>
<p>It’s much easier to generate such voltage pulses on-chip than it is to generate multiple microwave fields. The solution requires only a single control cable and removes obtrusive on-chip microwave control circuitry. </p>
<p>For more than two decades global control in quantum computers remained an idea. Researchers could not devise a suitable technology that could be integrated with a quantum chip and generate microwave fields at suitably low powers.</p>
<p>In our work we show that a component known as a dielectric resonator could finally allow this. The dielectric resonator is a small, transparent crystal which traps microwaves for a short period of time. </p>
<p>The trapping of microwaves, a phenomenon known as resonance, allows them to interact with the spin qubits longer and greatly reduces the power of microwaves needed to generate the control field. This was vital to operating the technology inside the refrigerator.</p>
<p>In our experiment, we used the dielectric resonator to generate a control field over an area that could contain up to four million qubits. The quantum chip used in this demonstration was a device with two qubits. We were able to show the microwaves produced by the crystal could flip the spin state of each one.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/415815/original/file-20210812-26-1twkkg8.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">Illustration of a crystal dielectric resonator producing a global control field in a spin quantum processor.</span>
<span class="attribution"><span class="source">Tony Melov</span></span>
</figcaption>
</figure>
<h2>The path to a full-scale quantum computer</h2>
<p>There is still work to be done before this technology is up to the task of controlling a million qubits. For our study, we managed to flip the state of the qubits, but not yet produce arbitrary superposition states. </p>
<p>Experiments are ongoing to demonstrate this critical capability. We’ll also need to further study the impact of the dielectric resonator on other aspects of the quantum processor.</p>
<p>That said, we believe these engineering challenges will ultimately be surmountable — clearing one of the greatest hurdles to realising a large-scale spin-based quantum computer.</p>
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Read more:
<a href="https://theconversation.com/error-correcting-the-things-that-go-wrong-at-the-quantum-computing-scale-84846">Error correcting the things that go wrong at the quantum computing scale</a>
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<img src="https://counter.theconversation.com/content/165956/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jarryd Pla receives funding from the Australian Research Council. He is also an inventor on patents related to quantum computing.</span></em></p><p class="fine-print"><em><span>Andrew Dzurak receives research funding from the Australian Research Council and the US Army Research Office. He is a member of the Executive Board of the Sydney Quantum Academy and a member of the Executive of the ARC Centre of Excellence for Quantum Computation and Communication Technology. He is also an inventor on a number of patents related to quantum computing.</span></em></p>So far researchers have only been able to control a handful of qubits — the basic units of information in a quantum computer. A new approach could help them control millions at a time.Jarryd Pla, Senior Lecturer in Quantum Engineering, UNSW SydneyAndrew Dzurak, Scientia Professor in Quantum Engineering, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1265032019-12-03T12:58:03Z2019-12-03T12:58:03ZA quantum computing future is unlikely, due to random hardware errors<figure><img src="https://images.theconversation.com/files/304539/original/file-20191130-156095-1m7msum.jpg?ixlib=rb-1.1.0&rect=603%2C11%2C3069%2C2121&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Will quantum computers ever reliably best classical computers?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-render-qubits-1015677376">Amin Van/Shutterstock.com</a></span></figcaption></figure><figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=801&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=801&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=801&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1007&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1007&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303588/original/file-20191125-74588-1s17qy1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1007&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s rendition of the Google processor.</span>
<span class="attribution"><a class="source" href="https://ai.googleblog.com/2019/10/quantum-supremacy-using-programmable.html">Forest Stearns, Google AI Quantum Artist in Residence</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p><a href="https://www.nature.com/articles/s41586-019-1666-5">Google announced</a> this fall to much fanfare that it had demonstrated “quantum supremacy” – that is, it performed a specific quantum computation far faster than the best classical computers could achieve. IBM <a href="https://www.quantamagazine.org/google-and-ibm-clash-over-quantum-supremacy-claim-20191023/">promptly critiqued the claim</a>, saying that its own classical supercomputer could perform the computation at <a href="https://www.ibm.com/blogs/research/2019/10/on-quantum-supremacy/">nearly the same speed with far greater fidelity</a> and, therefore, the Google announcement should be taken “with a large dose of skepticism.”</p>
<p>This wasn’t the first time someone cast doubt on quantum computing. Last year, <a href="https://scholar.google.com/citations?user=EsHfKvUAAAAJ&hl=en&oi=sra">Michel Dyakonov</a>, a theoretical physicist at the University of Montpellier in France, offered a slew of technical reasons <a href="https://spectrum.ieee.org/computing/hardware/the-case-against-quantum-computing">why practical quantum supercomputers will never be built</a> in an article in IEEE Spectrum, the flagship journal of electrical and computer engineering.</p>
<p>So how can you make sense of what is going on?</p>
<p>As someone who has worked on <a href="https://arxiv.org/abs/quant-ph/0206144">quantum computing</a> for <a href="https://arxiv.org/abs/quant-ph/0503027">many years</a>, I believe that due to the inevitability of random errors in the hardware, useful quantum computers are unlikely to ever be built. </p>
<h2>What’s a quantum computer?</h2>
<p>To understand why, you need to understand how quantum computers work since they’re fundamentally different from classical computers.</p>
<p>A classical computer uses 0s and 1s to store data. These numbers could be voltages on different points in a circuit. But a quantum computer works on quantum bits, also known as qubits. You can picture them as waves that are associated with amplitude and phase.</p>
<p>Qubits have special properties: They can exist in superposition, where they are both 0 and 1 at the same time, and they may be entangled so they share physical properties even though they may be separated by large distances. It’s a behavior that does not exist in the world of classical physics. The <a href="https://en.wikipedia.org/wiki/Quantum_superposition">superposition vanishes when the experimenter interacts</a> with the quantum state. </p>
<p>Due to superposition, a quantum computer with 100 qubits can represent 2<sup>100</sup> solutions simultaneously. For certain problems, this exponential parallelism can be harnessed to create a tremendous speed advantage. Some <a href="https://www.technologyreview.com/s/613596/how-a-quantum-computer-could-break-2048-bit-rsa-encryption-in-8-hours/">code-breaking problems could be solved exponentially faster on a quantum machine</a>, for example.</p>
<p>There is another, narrower approach to quantum computing called <a href="https://en.wikipedia.org/wiki/Quantum_annealing">quantum annealing</a>, where qubits are used to speed up optimization problems. D-Wave Systems, based in Canada, has built optimization systems that use qubits for this purpose, but critics also claim that these systems <a href="https://www.theverge.com/2014/6/19/5824336/google-s-quantum-computer-just-flunked-its-first-big-test">are no better than classical computers</a>.</p>
<p>Regardless, companies and countries are investing massive amounts of money in quantum computing. China has developed a <a href="https://www.scmp.com/news/china/society/article/2110563/china-building-worlds-biggest-quantum-research-facility">new quantum research facility worth US$10 billion</a>, while the European Union has developed a €1 billion ($1.1 billion) <a href="https://ec.europa.eu/digital-single-market/en/news/european-commission-will-launch-eu1-billion-quantum-technologies-flagship">quantum master plan</a>. The United States’ <a href="https://www.technologyreview.com/f/612679/president-trump-has-signed-a-12-billon-law-to-boost-us-quantum-tech/">National Quantum Initiative Act</a> provides $1.2 billion to promote quantum information science over a five-year period.</p>
<p>Breaking encryption algorithms is a powerful motivating factor for many countries – if they could do it successfully, it would give them an enormous intelligence advantage. But these investments are also promoting fundamental research in physics. </p>
<p><a href="https://www.predictiveanalyticstoday.com/what-is-quantum-computing/">Many companies are pushing to build quantum computers</a>, including Intel and Microsoft in addition to Google and IBM. These companies are trying to build hardware that replicates the circuit model of classical computers. However, current experimental systems have less than 100 qubits. To achieve useful computational performance, you probably need machines with hundreds of thousands of qubits.</p>
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<a href="https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/303589/original/file-20191125-74588-j0a746.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=496&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">Google’s Sycamore processor has only 54 qubits.</span>
<span class="attribution"><a class="source" href="https://ai.googleblog.com/2019/10/quantum-supremacy-using-programmable.html">Erik Lucero, Research Scientist and Lead Production Quantum Hardware, Google</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Noise and error correction</h2>
<p>The mathematics that underpin quantum algorithms is well established, but there are daunting engineering challenges that remain. </p>
<p>For computers to function properly, they must correct all small random errors. In a quantum computer, such errors arise from the non-ideal circuit elements and the interaction of the qubits with the environment around them. For these reasons the qubits can lose coherency in a fraction of a second and, therefore, the computation must be completed in even less time. If random errors – which are inevitable in any physical system – are not corrected, the computer’s results will be worthless.</p>
<p>In classical computers, small noise is corrected by taking advantage of a concept known as thresholding. It works like the rounding of numbers. Thus, in the transmission of integers where it is known that the error is less than 0.5, if what is received is 3.45, the received value can be corrected to 3.</p>
<p>Further errors can be corrected by introducing redundancy. Thus if 0 and 1 are transmitted as 000 and 111, then at most one bit-error during transmission can be corrected easily: A received 001 would be a interpreted as 0, and a received 101 would be interpreted as 1.</p>
<p>Quantum error correction codes are a generalization of the classical ones, but there are crucial differences. For one, the unknown qubits cannot be copied to incorporate redundancy as an error correction technique. Furthermore, errors present within the incoming data before the error-correction coding is introduced cannot be corrected. </p>
<h2>Quantum cryptography</h2>
<p>While the problem of noise is a serious challenge in the implementation of quantum computers, it isn’t so in quantum cryptography, where people are dealing with single qubits, for single qubits can remain isolated from the environment for significant amount of time. Using quantum cryptography, two users can exchange the very large numbers known as keys, which secure data, without anyone able to break the key exchange system. Such key exchange could help secure communications between satellites and naval ships. But the actual encryption algorithm used after the key is exchanged remains classical, and therefore the encryption is theoretically no stronger than classical methods.</p>
<p>Quantum cryptography is being commercially used in a limited sense for high-value banking transactions. But because the two parties must be authenticated using classical protocols, and since a chain is only as strong as its weakest link, it’s not that different from existing systems. Banks are still using a classical-based authentication process, which itself could be used to exchange keys without loss of overall security. </p>
<p>Quantum cryptography technology <a href="https://www.extremetech.com/extreme/287094-quantum-cryptography#disqus_thread">must shift its focus to quantum transmission of information</a> if it’s going to become significantly more secure than existing cryptography techniques. </p>
<h2>Commercial-scale quantum computing challenges</h2>
<p>While quantum cryptography holds some promise if the problems of quantum transmission can be solved, I doubt the same holds true for generalized quantum computing. Error-correction, which is fundamental to a multi-purpose computer, is such a significant challenge in quantum computers that I don’t believe they’ll ever be built at a commercial scale.</p>
<p>[ <em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>. ]</p><img src="https://counter.theconversation.com/content/126503/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Subhash Kak 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>Google claims quantum supremacy – IBM says not so fast. One researcher explains why he doesn’t see quantum computers outpacing classical computers any time soon … and maybe not ever.Subhash Kak, Regents Professor of Electrical and Computer Engineering, Oklahoma State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1272552019-11-19T18:22:53Z2019-11-19T18:22:53ZQuantum computing, the new frontier of finance<figure><img src="https://images.theconversation.com/files/302156/original/file-20191118-66953-pqj5x8.jpg?ixlib=rb-1.1.0&rect=0%2C111%2C1526%2C1055&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Close-up on the circuitry of the Vesuvius quantum computer, announced in 2012 by the Canadian firm D-Wave Systems.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/jurvetson/39188582795">Steve Jurvetson/Flickr</a></span></figcaption></figure><p>The evolution of modern finance was closely linked to the evolution of computers, communications, and financial mathematics. Two main changes happened in the 1970s with the beginning of derivative trading and after the crisis of 2007 with the massive introduction of fintech.</p>
<p>Derivatives pricing started with the celebrated <a href="https://www.investopedia.com/terms/b/blackscholes.asp">Black and Scholes equation</a> and formulas in 1974, followed by a wealth of mathematical methods to compute the prices of derivatives. Still, even the 1980s derivative pricing required supercomputers, giving big firms a major competitive advantage – before the 2007 crisis, the trading volume was close to 1 trillion dollars a day. The prevailing opinion was that derivatives had enabled us to complete financial markets so that any stream of cash flows could be engineered.</p>
<p>This belief was shattered by the <a href="https://www.nytimes.com/2018/09/12/upshot/financial-crisis-recession-recovery.html">2007 financial crisis</a>, which showed that hedging can be perfect only as long as counterparties stay solvent. With the <a href="https://www.nytimes.com/2018/09/17/opinion/lehman-brothers-financial-crisis.html">failure of Lehman Brothers</a>, the world of finance became painfully understood that there is risk in derivatives and that free markets are not self-regulating. To save them, central banks injected trillions of dollars, euros and yens in liquidity through <a href="https://www.investopedia.com/terms/q/quantitative-easing.asp">quantitative easing</a> (QE). In the United States, the Fed injected some 4.5 trillion dollars in liquidity, roughly <a href="https://fred.stlouisfed.org/">one-third of the total monetary mass</a>.</p>
<h2>Understanding clients and mitigating problems</h2>
<p>After the crisis, the financial world turned its attention to understanding clients and to mitigate the problems created by market manipulations made possible by automated trading. Fintech uses computer-based techniques to model client behaviour, to automate dealing with clients and to plan and execute trades. At the same time, a number of <a href="https://www.investopedia.com/terms/f/flash-crash.asp">“flash crashes”</a> – sudden but short-lived large drops in market value – has heightened the attention of major players to the risk of crowding of algorithms.</p>
<p>A major new change is now in sight through the possible implementation of quantum computers. Instead of binary bits – the classic elementary unit of information – quantum computing uses <a href="https://en.wikipedia.org/wiki/Qubit">qubits</a> (quantum bits), obtained by the superposition of binary states. This would allow them to process a much larger amount of information thousands of times faster than classical computers. </p>
<p>It was generally believed that quantum computing was far in the future, but Google has recently announced to have actually reached this goal. First, the <a href="https://www.ft.com/content/b9bb4e54-dbc1-11e9-8f9b-77216ebe1f17"><em>Financial Times</em> reported</a> that Google had posted a paper on the NASA website announcing that its quantum computer called Sycamore has been able to perform in three minutes a computation that would take 10,000 years to perform on classical supercomputers. The paper was later removed from the website, but Google confirmed the announcement with an <a href="https://www.nature.com/articles/d41586-019-03224-w">October 23 paper in <em>Nature</em></a> and invited scientists and journalists to <a href="https://www.nytimes.com/2019/10/30/opinion/google-quantum-computer-sycamore.html">watch the computation</a>.</p>
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<figcaption><span class="caption">Google claims “quantum computer supremacy” with new processor (ABC News).</span></figcaption>
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<h2>Quantum leaps</h2>
<p>Why is it so important to reach <a href="https://en.wikipedia.org/wiki/Quantum_supremacy">quantum supremacy</a>? Modern economies are shaped by complex computations. Supercomputers are used to design products such as cars and planes, invent new drugs, create electronic circuits, model economies, organise large-scale logistics and study the climate. Unfortunately, computations also allow us to build lethal weapons and, increasingly, to monitor and attempt to control the behaviour of populations.</p>
<p>In the last 70 years, computing power has increased by a mind-boggling multiple. In the 1960s, even powerful computers were able to perform only a few MFLOPS (millions of floating point operations per second) while today the most powerful computer is able to perform almost <a href="https://www.theverge.com/circuitbreaker/2018/6/12/17453918/ibm-summit-worlds-fastest-supercomputer-america-department-of-energy">100 PetFLOPS</a> (10 raised to 17th power).</p>
<p>Even with such power, there are important computational tasks that are not solvable or only partially solvable today. The study of combustion and turbulence, the study of molecules from basic physical principles (quantum-mechanical simulation), engineering nuclear fusion and even logistic problems are some of the grand Challenges of computation as defined by federal <a href="http://www.hpcc.gov/">High Performance Computing and Communications</a> (HPCC) program. Solving these problems would give a firm or even a nation an important competitive advantage. There is, of course, also the sinister possibility of creating more destructive weapons.</p>
<p>What would be the importance of quantum supremacy for finance and economics? First, quantum computing would make current cryptographic techniques unsafe. Methods and algorithms will have to be changed. <a href="https://www.technologyreview.com/s/613946/explainer-what-is-post-quantum-cryptography/">Post-quantum cryptography</a>, or quantum-resistant cryptography, is a flourishing sector of study both in academia and with firms involved in cryptography. Some firms already offer products for post-quantum cryptography, which will be big business.</p>
<h2>Intuition, not brute force</h2>
<p>But probably the major changes would be in artificial intelligence (AI) and machine learning. The fact is that we do not know how human intuition and problem-solving works. Ultimately, computers solve problems with a brute-force approach by looking at different alternatives and choosing the best. The search space of quantum computers could be thousands of time larger than the search space considered by current computers. It would become feasible to synthesise a design from specifications and machines could become more “creative” through the ability to explore an immense range of possible design solutions. In the fields of finance and economics, quantum computing could lead to analysing a large space of heterogeneous data to make financial and predictions and understanding economic phenomena. </p>
<p>Amid such hope, caution is necessary: financial and economic data are truly complex, and analysis will not necessarily lead to more accurate predictions given the complexity of data. The complexity and non-stationarity of data might defy analysis. In other words, it is questionable if the use of quantum computing will reduce uncertainty.</p>
<p>The global effect of quantum computing on economic and social life will depend on the use that will be made of this tool – and that stems from human decisions rather than being forced by knowledge itself.</p><img src="https://counter.theconversation.com/content/127255/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Les auteurs ne travaillent pas, ne conseillent pas, ne possèdent pas de parts, ne reçoivent pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'ont déclaré aucune autre affiliation que leur organisme de recherche.</span></em></p>On October 23 Google announced that it built a quantum computer thousands of times faster than classic computers. This could have immense impacts on finance, cryptography and other fields.Sergio Focardi, Enseignant-chercheur en Finance quantitative à l’ESILV et à l'EMLV, membre du De Vinci Research Center, Pôle Léonard de VinciDavide Mazza, Professor of Finance, Pôle Léonard de VinciLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1240822019-09-26T04:05:11Z2019-09-26T04:05:11ZWhy are scientists so excited about a recently claimed quantum computing milestone?<figure><img src="https://images.theconversation.com/files/293991/original/file-20190925-51438-z6d76t.jpg?ixlib=rb-1.1.0&rect=19%2C0%2C3176%2C2011&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Researchers from Google may have demonstrated 'quantum supremacy' for the first time, opening pathways to a new era of computation.</span> <span class="attribution"><a class="source" href="https://ai.googleblog.com">Google</a></span></figcaption></figure><p>A quantum computer may have solved a problem in minutes that would take the fastest conventional supercomputer more than 10,000 years. A draft of a paper by Google researchers laying out the achievement leaked in recent days, <a href="https://www.ft.com/content/b9bb4e54-dbc1-11e9-8f9b-77216ebe1f17">setting off</a> an avalanche of news coverage and speculation. </p>
<p>While the research has not yet been peer-reviewed – the final version of the paper is expected to appear soon – if it all checks out it would represent “the first computation that can only be performed on a quantum processor”. </p>
<p>That sounds impressive, but what does it mean?</p>
<h2>Quantum computing: the basics</h2>
<p>To understand why quantum computers are a big deal, we need to go back to conventional, or digital, computers.</p>
<p>A computer is a device that takes an input, carries out a sequence of instructions, and produces an output. In a digital computer, these inputs, instructions and outputs are all sequences of 1s and 0s (individually called bits). </p>
<p>A quantum computer does the same thing, but it uses <em>quantum</em> bits, or qubits. Where a bit takes on only one of two values (1 or 0), a qubit uses the complex mathematics of quantum mechanics, providing a richer set of possibilities. </p>
<p>Building quantum computers takes phenomenal engineering. They must be isolated to ensure nothing interferes with the delicate quantum states of the qubits. This is why they are kept in vacuum chambers containing fewer particles than outer space, or in refrigerators colder than anything in the universe. </p>
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<a href="https://theconversation.com/quantum-computers-could-arrive-sooner-if-we-build-them-with-traditional-silicon-technology-123115">Quantum computers could arrive sooner if we build them with traditional silicon technology</a>
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<p>But at the same time, you need a way to interact with the qubits to carry out instructions on them. The difficulty of this balancing act means that the size of quantum computers has grown slowly. </p>
<p>However, as the number of qubits connected together in a quantum computer grows, it becomes exponentially more complicated to imitate its behaviour with a digital computer. Adding a single qubit to your quantum computer could double the amount of time it would take a digital computer to carry out equivalent calculations. </p>
<p>By the time you get up to 53 qubits – that’s how many are in the Sycamore chip used by the Google researchers – the quantum computer can quickly perform calculations that would take our biggest digital computers (supercomputing clusters) thousands of years.</p>
<h2>What is quantum supremacy?</h2>
<p>Quantum computers won’t be faster than digital computers for everything. We know they will be good at factorising large numbers (which is bad news for online security) and simulating some physical systems like complex molecules (which is good news for medical research). But in many cases they will have no advantage, and researchers are still working out exactly what kinds of calculations they can speed up and by how much.</p>
<p><a href="https://arxiv.org/abs/1203.5813">Quantum supremacy was the name given</a> to the hypothetical point at which a quantum computer could perform a calculation no conceivable digital computer could perform in a reasonable amount of time. </p>
<p>The Google researchers now appear to have performed such a calculation, although the calculation itself is at first sight uninspiring. </p>
<p>The task is to execute a sequence of random instructions on the quantum computer, then output the result of looking at its qubits. For a big enough number of instructions, this becomes <a href="https://www.nature.com/articles/nature23458">very hard to mimic</a> with a digital computer.</p>
<h2>Useful quantum computers still not in sight</h2>
<p>The idea of quantum supremacy is popular because it is a graspable milestone – a valuable currency in the highly competitive area of quantum computing research. </p>
<p>Google’s achievement is technically impressive because it required full programmability on the 53-qubit chip. But the task performed was designed specifically to demonstrate quantum supremacy, and nothing more. It is not known whether such a device can perform any other calculations that a digital computer cannot also do. In other words, this does not signal the arrival of quantum computing.</p>
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Read more:
<a href="https://theconversation.com/in-the-future-everyone-might-use-quantum-computers-112063">In the future, everyone might use quantum computers</a>
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<p>A usable general-purpose quantum computer will need to be much larger. Instead of 53 qubits, it will require millions. (Strictly speaking, it will require thousands of nearly error-free qubits, but producing those will involve millions of noisy qubits like those in the Google device.) </p>
<p>Ubiquitous quantum computing is still far enough away that attempting to predict when it will occur and what useful tasks it will eventually be used for is a <a href="https://www.pcworld.com/article/155984/worst_tech_predictions.html">recipe for embarrassment</a> because history teaches us that unforeseen applications will blossom as access to new tools becomes available. </p>
<h2>A new tool for science</h2>
<p>From a scientific point of view, the future of quantum computation is now much more exciting. </p>
<p>On one hand, quantum computation is confronting. In the same way the outputs of early digital computers could be verified by hand calculations, the outputs of quantum computers have until now been verifiable by digital computers. </p>
<p>This is no longer the case. But that is good, because now these new devices give us new scientific tools. Just running these devices produces exotic physics that we have never encountered in nature. Simulating quantum physics in this new regime could provide new insights into all areas of science, all the way from more detailed understandings of biological processes to probing the possible effects quantum physics has on spacetime. </p>
<p>Quantum computation represents a fundamental shift that is now under way. What is most exciting is not what we can do with with a quantum computer today, but the undiscovered truths it will reveal tomorrow.</p><img src="https://counter.theconversation.com/content/124082/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Ferrie receives funding from the Australian Research Council and the Australian Department of Industry, Innovation and Science. He also has a vested interest the success of quantum computing so he can sell more copies of his book Quantum Computing for Babies.</span></em></p>A leaked research paper shows that quantum computer researchers may have overtaken conventional ones for the first timeChristopher Ferrie, Senior Lecturer, UTS Chancellor's Postdoctoral Research and ARC DECRA Fellow, University of Technology SydneyLicensed as Creative Commons – attribution, no derivatives.