Quantum computing and quantum supremacy

Recently, Google claimed that it had achieved quantum supremacy – the point at which a quantum computer can perform a task that would be impossible for a conventional computer (or would take so long it would be entirely impractical for a conventional computer). To achieve quantum supremacy, Google’s quantum computer completed a calculation in 200 seconds that Google claimed would have taken even the most powerful supercomputer 10,000 years to complete. But what is quantum computing? And how does it work?

What is quantum computing?

Traditional computers are, at their heart, very fast versions of the simplest electronic calculators. They are only capable of processing one “bit” of information at a time, in the form of a binary 1 or 0. Each bit is like an on/off switch, that can either be in the off position – represented by a zero – or in the on position – represented by a one. Every app you use, website you visit and photograph you take, no matter how complex, is ultimately made up of millions of these bits in some combination of ones and zeroes. This works great for most things, but it doesn’t reflect the way the universe actually works. In nature, things aren’t just on or off.

But quantum computers don’t rely on bits; they use “qubits”. Qubits, thanks to the marvels of quantum mechanics, can also be in what’s called ‘superposition’. They could be both on and off at the same time, or exist somewhere in between. This allows quantum computers to look at many different variables at the same time, which means they can crunch through more scenarios in a much shorter space of time than even the fastest computers available today.

How do quantum computers work?

Take a coin. If you flip it, it can either be heads or tails. But if you spin it – it’s got a chance of landing on heads, and a chance of landing on tails. Until you measure it, by stopping the coin, it can be either. Superposition is like a spinning coin, and it’s one of the things that makes quantum computers so powerful. A qubit allows for uncertainty.

If you ask a normal computer to figure its way out of a maze, it will try every single branch in turn, ruling them all out individually until it finds the right one. A quantum computer can go down every path of the maze at once. It can hold uncertainty in its head.

The other thing that qubits can do is called entanglement. Normally, if you flip two coins, the result of one coin toss has no bearing on the result of the other one. They’re independent. In entanglement, two particles are linked together, even if they’re physically separate. If one comes up heads, the other one will also be heads.

It sounds like magic, and physicists still don’t fully understand how or why it works. But in the realm of quantum computing, it means that you can move information around, even if it contains uncertainty. You can take that spinning coin and use it to perform complex calculations. And if you can string together multiple qubits, you can tackle problems that would take our best computers millions of years to solve.

What can quantum computers do?

Reaching quantum supremacy is clearly an important milestone, yet we’re still a long way from commercially available quantum computers hitting the market. Right now, current quantum computing work is limited to labs and major tech players like Google, IBM, and Microsoft.

Strengthening cyber security: Right now, a lot of encryption systems rely on the difficulty of breaking down large numbers into prime numbers. This is called factoring, and for classical computers, it’s slow, expensive and impractical. But quantum computers can do it easily. And that could put our data at risk.

The only way to fight back is with quantum encryption. This relies on the uncertainty principle – the idea that you can’t measure something without influencing the result. Quantum encryption keys could not be copied or hacked. They would be completely unbreakable.'

Modeling traffic flows to improve our cities: They have the potential to rapidly accelerate the development of artificial intelligence. Google is already using them to improve the software of self-driving cars.

Developing new medicines and new materials: Right now, supercomputers can only analyse the most basic molecules. But quantum computers operate using the same quantum properties as the molecules they’re trying to simulate. They should have no problem handling even the most complicated reactions.

That could mean more efficient products – from new materials for batteries in electric cars, through to better and cheaper drugs, or vastly improved solar panels. Scientists hope that quantum simulations could even help find a cure for Alzheimer’s.

Quantum computers will find a use anywhere where there’s a large, uncertain complicated system that needs to be simulated. That could be anything from predicting the financial markets, to improving weather forecasts, to modelling the behaviour of individual electrons: using quantum computing to understand quantum physics.

Reaching quantum supremacy?

The term quantum supremacy was coined in 2012 by John Preskill, a professor of theoretical physics. By his definition, quantum supremacy is the point where a quantum computer is able to solve a problem that no traditional computer could within a reasonable amount of time. In any case, the term caught on, and it has been embraced with particular zeal by the Google AI Quantum team.

The quantum supremacy milestone allegedly achieved by Google is a pivotal step in the quest for practical quantum computers. The fact that Google was able to achieve quantum supremacy means that they were not only able to calculate things very quickly, faster than any normal computer or even a supercomputer, but that they could find the correct results amid all the wrong ones which the quantum machine also spit out.

While there’s currently no practical use for the milestone, much is at stake as countries and companies compete across the quantum landscape. The emerging technology is anticipated to radically transform modern communication and security, accelerate powerful new discoveries and support the design of first-of-a-kind chemicals and materials.

“This achievement, if it holds up under the intense scrutiny that is sure to follow, represents a landmark academic achievement relating to the overall value of quantum computers,” Biercuk said. “Accordingly, this really takes the legs out from under the few naysayers claiming quantum computers have no future.”

And members across the global quantum community already seem to be energized by the announcement. Michael Biercuk, experimental quantum physicist and founder and CEO of Q-CTRL, a Sydney, Australia-based quantum computing startup that recently opened offices in Los Angeles, told Nextgov that the demonstration marks an important incremental step in the long-running effort to build useful quantum technology.

And for Google, Pichai said this is only the beginning. Quantum computing holds as much promise for the company’s future as other groundbreaking technologies, such as artificial intelligence. Pichai also compared the newly-unveiled breakthrough to the Wright brothers’ monumental first flight.

“The first plane flew only for 12 seconds, and so there is no practical application of that,” he said. “But it showed the possibility that a plane could fly.”