Explainer: Quantum physics

Without quantum mechanics, we would not have the transistor. IvyMike/Flickr

This might surprise you, but there may be literally thousands, or even tens of thousands, of devices and components surrounding you right now that work because of our understanding of quantum physics.

Before you ask, it doesn’t include your dishwasher detergent.

Quantum Physics is a branch of science that engenders huge amounts of interest, awe, and, more often than not, bewilderment. But before we can tell you how it really impacts you, we need to provide a little bit of background.

OK, give me the theory

Quantum Physics is focused on explaining the behavior of matter and light at very small scales – single atoms and photons (“particles” of light). The mathematical formalism of quantum mechanics (distinguished from the broader term quantum physics) allows scientists to model the physics being probed through experiments.

There’s nothing unique about quantum physics – it’s a scientific theory just like any other, meeting the rigorous requirements of the scientific method.

But there are certainly some strange aspects of the theory.

The word “quantum” is defined by the Oxford English Dictionary as meaning a quantity, share, or portion. It was applied to pioneering studies of the nature of light and matter because experiments suggested that a wide variety of measures came with only very particular allowed values – quite contrary to what we generally observe in the world around us, or standard physical intuition.

It gets stranger.

In quantum physics nobody can tell you much with any certainty. They can only describe probabilities for measurement outcomes (e.g. where a particle might be). And quantum physics describes light as being both a particle and a wave at the same time.

Why is the theory so counterintuitive? Well, unfortunately that remains the subject of much study, including the active research field of quantum foundations, trying to elucidate what’s really going on.

Despite these quirks, quantum physics has become one of the most successful scientific theories developed to date, permitting scientists to explain a range of behaviors in systems from stars to gases, metals to light.

Most importantly, the theory has predictive power, a key requirement in science.

What about all those quantum applications?

Let’s begin with IT.

Transistors are the fundamental hardware elements in microprocessors – they represent bits of information in the way they conduct electricity (on = 1, off = 0).

Transistors are fabricated from materials known as semiconductors, in which charge-carrying electrons are only allowed to occupy certain discrete energy levels, as determined by quantum physics. As more electrons are added they form allowed “bands” in a prescribed manner.

The resultant energy “bandstructure,” which can be modified by applying voltages to wires connected to the device, gives rise to the switching behavior from which we build fundamental electrical elements.

Without quantum mechanics we would have no understanding of semiconductors, could not have engineered the transistor, and thus would have no microprocessors.

Similar things can be said about other familiar IT devices in your office. Mobile phones, for instance, use high-frequency circuits that function thanks to the same physics.

On the internet, network time is kept by atomic clocks which use the quantum description of atoms and light-matter interactions to produce an extremely stable and repeatable “tick.”

In fact, almost every piece of information technology hardware – from microprocessors in desktops and servers to optoelectronic modulators and laser diodes used in long distance communications for the internet owe their existence to our understanding of quantum physics.

Anything outside the office?

At home, if you turn on your flatpanel television it may well have what’s known as an LED-backlit display. This uses an energy-efficient light source know as a light-emitting diode.

The quantum physics of semiconductor bandstructure and Planck’s theory of radiation explain how to produce light of various colours from these devices.

Your home entertainment system may also have a DVD player that uses a solid-state laser, the development of which was based on Einstein’s quantum theory of radiation and later developments in stimulated emission.

Or if you had an MRI for a knee injury, that functioned thanks to developments in nuclear magnetic resonance and the quantum theory of “spin” angular momentum. We could go on and on …

To be clear, these aren’t technologies that can be torturously traced back to quantum theory – these are devices and systems that were developed explicitly because of our knowledge of quantum physics.

So now you know

The real, everyday impacts of quantum physics have been obscured by marketers who use the word “quantum” relentlessly to suggest that their products are “high-tech,” in applications as diverse as data storage and, yes, dishwasher detergent. Similarly, New-age groups have co-opted “quantum” and used it to mean pretty much any absurd pseudo-religious idea they wish.

All of this is bunk.

But now if someone tries to sell you something because it’s “quantum” you can separate truth from nonsense.

And if you question why this branch of physics matters to you, just look around and you’ll see the answer in nearly all of modern technology.