Interactive quantum advantage with noisy, shallow Clifford circuits

Abstract

Recent work by Bravyi et al. constructs a relation problem that a noisy constant-depth quantum circuit (QNC 0 ) can solve with near certainty (probability 1 − o(1)), but that any bounded fan-in constant-depth classical circuit (NC 0 ) fails with some constant probability. We show that this robustness to noise can be achieved in the other low-depth quantum/classical circuit separations in this area. In particular, we show a general strategy for adding noise tolerance to the interactive protocols of Grier and Schaeffer. As a consequence, we obtain an unconditional separation between noisy QNC 0 circuits and AC 0 [p] circuits for all primes p ≥ 2, and a conditional separation between noisy QNC 0 circuits and log-space classical machines under a plausible complexity-theoretic conjecture.A key component of this reduction is showing average-case hardness for the classical simulation tasks-that is, showing that a classical simulation of the quantum interactive task is still powerful even if it is allowed to err with constant probability over a uniformly random input. We show that is true even for quantum tasks which are ⊕L-hard to simulate. To do this, we borrow techniques from randomized encodings used in cryptography.