Abstract
We study the problem of generating independent samples from the output distribution of Google’s Sycamore quantum circuits with a target fidelity, which is believed to be beyond the reach of classical supercomputers and has been used to demonstrate quantum supremacy. We propose a method to classically solve this problem by contracting the corresponding tensor network just once, and is massively more efficient than existing methods in generating a large number of uncorrelated samples with a target fidelity. For the Sycamore quantum supremacy circuit with 53 qubits and 20 cycles, we have generated uncorrelated bitstrings which are sampled from a distribution , where the approximate state has fidelity . The whole computation has cost about 15 h on a computational cluster with 512 GPUs. The obtained samples, the contraction code and contraction order are made public. If our algorithm could be implemented with high efficiency on a modern supercomputer with ExaFLOPS performance, we estimate that ideally, the simulation would cost a few dozens of seconds, which is faster than Google’s quantum hardware.
- Received 20 November 2021
- Accepted 20 July 2022
DOI:https://doi.org/10.1103/PhysRevLett.129.090502
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