The race to build the first useful quantum computer continues apace. And, like all races, there are decisions to be made, including the technology each competitor must choose. But, in science, no one knows the race course, where the finish line is, or even if the race has any sort of prize (financial or intellectual) along the way.
On the other hand, the competitors can take a hand in the outcome by choosing the criteria by which success is judged. And, in this rather cynical spirit, we come to IBM’s introduction (PDF) of “quantum volume” as a single numerical benchmark for quantum computers. In the world of quantum computing, it seems that everyone is choosing their own benchmark. But, on closer inspection, the idea of quantum volume has merit.
Many researchers benchmark using gate speed—how fast a quantum gate can perform an operation—or gate fidelity, which is how reliable a gate operation is. But these single-dimensional characteristics do not really capture the full performance of a quantum processor. For analogy, it would be like comparing CPUs by clock speed or cache size, but ignoring any of the other bazillion features that impact computational performance.