Google's method for checking quantum computer answers, for R&D teams
What it is: A quantum computer is a new kind of computer built on the physics of atoms. It works with qubits, the quantum version of an ordinary computer's bits, which lets it take on problems ordinary computers struggle with, such as how molecules behave. Today's machines are noisy: tiny disturbances cause small errors as they run, so their answers come out slightly wrong. The long-term fix, called error correction, is machines that repair their own errors while they work, and those are still being developed. Until they arrive, every answer is corrected afterwards by calculation, called error mitigation, and the authors expect it to stay useful even after. This paper, from Google's quantum research team, is a better method of error mitigation.
Who it's for: Any company paying for quantum computer work in chemistry or materials. A quantum computer's answer is only as good as the error mitigation behind it, and this method tells you whether to trust it. Machine time is bought in shots, single runs of the program, and in the authors' simulations this method needed 10 to 100 times fewer of them.
The catch: It is not yet proven on real hardware. Every new result in the paper comes from computer simulations of small, 16-qubit circuits; a circuit is the program a quantum computer runs. Only an earlier, simpler version has run on Google's own machine.