## Quantum computing is more than a concept now.

The fact that Google, in partnership with NASA, has achieved quantum supremacy will one day be a milestone studied in history books. It also bodes well for the United States because it means that despite rivals China, Russia and to a lesser extent North Korea having spent billions on their own quantum computing programs, we still achieved this remarkable feat first. That puts us well ahead in the quantum cold war that seems to be brewing.

Quantum computing has come a long way in a very short time. Back in 2016 when I talked with quantum scientists and put together an explainer piece for *Nextgov* about the differences between quantum and traditional computers, there were still quite a few experts who doubted that quantum computing would ever achieve anything useful. There were even noted scientists who believed the whole thing was a hoax.

Developing a new kind of computer system that uses quantum physics to calculate problems is necessary not only because of the speed it can offer, but also because we are nearing the limit of what we can do with traditional hardware. Right now, the typical size of a transistor inside most computers is 14 nanometers, which is incredibly small, about 500 times smaller than a single blood cell. Transistors are necessary because they enable computers to turn bits into a one or a zero. Electrons that are allowed to pass through the switch are given a value of one. Those that are blocked become zeros. But if your transistor is much smaller than 14 nanometers, electrons can sometimes ignore it, jumping to the other side of that barrier by a process called quantum tunneling. When that happens, we no longer reliably control calculations with some zeros becoming ones and fouling everything up.

Quantum computers by contrast use qubits, which are like the normal binary bits of a traditional computer. Most quantum machines use qubits made up of photons, which are pieces of electromagnetic radiation. The really magical thing about photons is that they can sometimes exist in a state known as superposition where they could become a one or a zero. Essentially, they are both at the same time. The rub is that as soon as you measure it, say by sending the photon through a filter, it will instantly collapse into either a one or a zero. Qubits can also become entangled with one another where their states are linked, and anything that affects one will instantly change the other regardless of how far apart they are at the time.

This weirdness is apparently not all that unusual when you get down into the tiny quantum world where electrons and atoms live, but seems strange to those of us existing in the physical world with different rules. Quantum computers can solve problems quickly because they are essentially looking at every possible solution at the same time. However, in terms of practicality, they will also output lots of solutions, including many wrong answers. The trick is pulling the one accurate answer from the pile of incorrect ones. Most of the research into quantum computers today involves not only trying to create machines with more qubits, but also figuring out ways to use properties like quantum entanglement and quantum manipulation, and working out mathematical equations in multi-dimensional vector spaces to locate correct answers amidst all the junk.

It’s really advanced to the point that even those working in the field are often stumped by some of the things that happen in the quantum world. That’s why Richard Feynman, one of the fathers of quantum mechanics, famously said that “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”

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. With the Google announcement, Preskill recently wrote a new column explaining that definition further. 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.

It’s worth noting that IBM, one of Google’s chief rivals in the quantum field, disputes whether Google achieved quantum supremacy at all. While Google claims that the test problem that was solved by their quantum computer would take supercomputers 10,000 years to solve, IBM disagrees. The company asserts that its supercomputer, using a “hierarchy of memories and high-precision computations in hardware, various software assets, and a vast knowledge base of algorithms” not considered by Google, could have achieved the same results in 2.5 days. And the company adds, it could be done with greater fidelity—meaning the traditional computer would not have outputted so many incorrect answers alongside the right one.

Google also gamed the system by creating a problem specifically tailored to their quantum machine, in this case executing a randomly chosen batch of instructions and then measuring the output string to make sure those calculations were done correctly. That setup also ensures that it would be difficult to repeat this process on a traditional machine for speed comparisons. The problem Google solved was basically a random one and has absolutely no practical value other than demonstrating that a quantum computer can calculate things very quickly with a reasonable amount of accuracy.

It’s still an important steppingstone and should be celebrated, if lightly. The real test, I believe, will be what comes next, and is a two-fold challenge. Preskill hints at the first part in his blog when he calls the current batch of quantum computers “noisy.” According to Preskill, the term “emphasizes that we have imperfect control over the qubits, resulting in small errors that accumulate over time; if we attempt too long a computation, we’re not likely to get the right answer.”

In other words, we have to better control the magic happening at the quantum level to weed out the incorrect answers and make results more accurate. Perhaps a hybrid quantum and traditional computer might be the answer with the quantum part of the machine eliminating millions of incorrect answers in a few seconds, and the traditional computer checking the outputted results the old fashion way, one by one, and selecting the only fully correct answer.

The second goal will be applying quantum computers to real problems, not ones made up in a lab to demonstrate a concept. Let’s apply quantum computing to something like diagnosing climate change and identifying ways we can halt, slow or reverse that process. Or perhaps we can find ways to better harness energy from solar panels. Who knows? Maybe we can make a longer-lasting lightbulb or develop transparent aluminum. Quantum supremacy is a fantastic milestone, so let’s celebrate quickly and get back to work on some practical problems.

*John Breeden II is an award-winning journalist and reviewer with over 20 years of experience covering technology. He is the CEO of the **Tech Writers Bureau**, a group that creates technological thought leadership content for organizations of all sizes. Twitter: @LabGuys*