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Quantum Computers Check Each Other's Work
sciencehabit writes "Quantum computers can solve problems far too complex for normal computers, at least in theory. That's why research teams around the globe have strived to build them for decades. But this extraordinary power raises a troubling question: How will we know whether a quantum computer's results are true if there is no way to check them? The answer, scientists now reveal, is that a simple quantum computer—whose results humans can verify—can in turn check the results of other dramatically more powerful quantum machines."
If a quantum computer makes a calculation in a forest and no one is around to verify it, does it solve the problem?
Many problems are NP-hard in one direction, but not the other way around. Use a quantum computer to find a solution, then use a classical computer/supercomputer to verify its results. Case in point: brute-forcing a hash function is hard, but computing the hash from a known value is easy; factoring large integers are hard, but multiplying two numbers are easily done.
It does not seem like their method truly verifies the solution. It only checks that the quantum computer is functioning correctly for specific problems with known solutions. By inserting these problems in many places in the quantum algorithm, they verify that the quantum computer was working correctly for the entire duration of the computation. Maybe that grants enough confidence in the solution... I don't know.
The thing is, most of those problems that take a thousand years to verify aren't generally interesting except perhaps in some esoteric field of study.
The interesting uses of QC, IMO involve things like cracking RSA, where the time required to verify a solution is trivial, but the time required to produce a solution is enormous.
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