Physicists have been talking about the power of quantum computing for over 30 years, but the questions have always been: will it ever do something useful and is it worth investing in? For such large-scale endeavors it is good engineering practice to formulate decisive short-term goals that demonstrate whether the designs are going in the right direction, write John Martinis, chief scientist for Quantum Hardware and Sergio Boixo, chief scientist for Quantum Computing Theory at Google AI Quantum in a blog post.
Google researchers devised an experiment as an important milestone to help answer these questions. This experiment, referred to as a quantum supremacy experiment, provided direction for the team to overcome the many technical challenges inherent in quantum systems engineering to make a computer that is both programmable and powerful. To test the total system performance, they selected a sensitive computational benchmark that fails if just a single component of the computer is not good enough.
They published the results of this quantum supremacy experiment in the Nature article, Quantum Supremacy Using a Programmable Superconducting Processor, having developed a new 54-qubit processor, named Sycamore comprised of fast, high-fidelity quantum logic gates, in order to perform the benchmark testing. The machine performed the target computation in 200 seconds, and from measurements in the experiment, they determined that it would take the world’s fastest supercomputer 10,000 years to produce a similar output.
The Sycamore quantum computer is fully programmable and can run general-purpose quantum algorithms. Since achieving quantum supremacy results last spring, the team has already been working on near-term applications, including quantum physics simulation and quantum chemistry, as well as new applications in generative machine learning, among other areas.
In a blog post, however, IBM disputed Google’s experiment results: Quantum computers are starting to approach the limit of classical simulation and it is important that we continue to benchmark progress and to ask how difficult they are to simulate. This is a fascinating scientific question.
Recent advances in quantum computing have resulted in two 53-qubit processors: one from our group in IBM and a device described by Google in a paper published in the journal Nature. In the paper, it is argued that their device reached “quantum supremacy” and that “a state-of-the-art supercomputer would require approximately 10,000 years to perform the equivalent task.” We argue that an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity. This is in fact a conservative, worst-case estimate, and we expect that with additional refinements the classical cost of the simulation can be further reduced.