Picture of Göran Johansson.
​“To me, Google's result is a huge source of inspiration. Now we know that it is possible to build a quantum computer – it requires hard work, but it can be done. It will be exciting to see how big quantum computers one manages to build within the next 5–10 years, ”says Göran Johansson, Professor of Applied Quantum Physics.​

Big breakthrough for quantum computers

​Researchers at Google have for the first time succeeded in solving a problem that is beyond the reach of a regular computer with a quantum computer. In just minutes, their quantum computer performed a computational task that, according to the researchers, would have taken more than ten thousand years for a powerful supercomputer. Göran Johansson, one of the leaders of Chalmers quantum computer project, sees this as a major milestone.
How did you feel when you heard of the news?
“I felt very happy! I knew that Google's research team was starting to get results with their 53-qubit quantum computer Sycamore, but that they have now managed to get such good reliability in their operations that they can perform this kind of calculation – it's a fantastic breakthrough!”

What lies behind the breakthrough?
“Sycamore is quite similar to Google's previous quantum computers in its structure. The breakthrough rather results from careful design of the hardware and software used to control the chip and a thorough analysis of which computational task to choose.”

Does this mean that quantum computers now outperform regular computers in general?
“No, absolutely not. The research team has shown that their quantum computer can solve a single calculation task better than a regular computer. The solved task is completely useless, it was chosen solely because it was judged to be easy to solve for a quantum computer but very difficult for a conventional one. But as quantum computers evolve, they will outperform conventional computers in more and more types of tasks.”

IBM criticizes Google’s calculations and states that their best supercomputer could solve the task in less than three days. What do you think about that?
“If that is the case, it would still be the first time a quantum computer performs something that requires the full capacity of the world's largest supercomputer, for almost three whole days, to reproduce. Whether it's ten thousand years or three days, I see the achievement of Google’s team as a very important step forward.”

What does this breakthrough mean to Chalmers quantum computer project?
“We are aiming for a quantum computer with one hundred well-functioning qubits, and Google has now shown that it is possible to create over fifty qubits that operate at over 99 percent reliability. It is incredibly inspiring and motivating!”

How does your quantum computer compare to Google’s?
“We use the same basic building blocks – superconducting circuits – as Google. So far, we are working, completely according to our plan, with a chip with only two qubits. Our strategy is to first get it to work really, really well on a small scale. For example, Google's qubits have an average lifetime of 16 microseconds, while we have over 80 microseconds. The longer the lifetime, the more computational operations you can do. On the other hand, Google has managed to reach significantly faster operations than we have, but we are working at getting really good at that as well. Then we will start to scale up in fairly large steps.”

What will be the next milestone in the development of quantum computers?
“Finding a useful problem that is beyond the reach of ordinary computers, but which a quantum computer with fifty to a hundred qubits can solve. We work intensively on this in collaboration with our industry partners. Probably, it will be within logistics or simulation of large molecules.”

Text: Ingela Roos
Photo: Johan Bodell

The article has previously been published in Swedish in Chalmers magasin #2 2019


Published: Wed 18 Dec 2019.