Ever since the first quantum computers were dreamt up in the early 1980s, researchers have looked forward to the day the devices could solve problems that are too difficult for classical computers. In the past five years, the machines have finally begun to challenge their classical cousins — although definitive victory over them has remained elusive.
Now, in the latest chapter of the battle to achieve this ‘quantum advantage’, researchers at Google say they have determined the conditions under which quantum computers can beat their classical counterparts. To understand these conditions, they used a quantum-computer processor named Sycamore to run random circuit sampling (RCS), a simple quantum algorithm that essentially generates a random sequence of values.
The team analysed Sycamore’s output and found that when it ran in a mode with a lot of noise interference while performing RCS, it could be ‘spoofed’, or beaten, by classical supercomputers. But, when the noise was lowered to a certain threshold, Sycamore’s computation became complex enough that spoofing it was effectively impossible — by some estimates, it would take the fastest classical supercomputer in the world ten trillion years. The finding, first reported in a preprint on the arXiv server last year, was published today in Nature1.
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