Chinese scientists have challenged Google’s 2019 claim of quantum supremacy by solving the same problem with a classical supercomputer within a reasonable time frame. The battery of 512 GPUs needed only 15 hours to complete a tweaked version of a known algorithm, whereas Google had estimated that it would take 10,000 years using the best available supercomputer at the time. The quantum calculation took 200 seconds and with a better supercomputer the researchers Chinese Academy of Sciences would probably be able to match that – or even do better.
There’s no universally accepted definition of quantum supremacy, but in any case it is a moving target. After all, classical hardware and algorithms keep improving. It’s therefore to be expected that quantum supremacy demonstrations are challenged, at least while the differences in calculation times are still relatively small. It should be noted, however, that Google’s Sycamore quantum computer required far fewer operations and less power than the supercomputer used by the Chinese Academy of Sciences.