Classical Simulation of Intermediate-Size Quantum Circuits

TL;DR

This paper presents a distributed classical simulation algorithm capable of simulating larger and deeper quantum circuits than previously possible, challenging the notion of quantum supremacy for certain random circuits.

Contribution

The authors introduce a new distributed simulation method that significantly extends the size and depth of quantum circuits that can be classically simulated.

Findings

Simulated an 8x8 qubit circuit with depth 40 in 2 minutes.

Successfully simulated larger 9x9 to 12x12 circuits with depths around 27-40.

Results suggest classical simulation can challenge claims of quantum supremacy for certain noisy circuits.

Abstract

We introduce a distributed classical simulation algorithm for general quantum circuits, and present numerical results for calculating the output probabilities of universal random circuits. We find that we can simulate more qubits to greater depth than previously reported using the cluster supported by the Data Infrastructure and Search Technology Division of the Alibaba Group. For example, computing a single amplitude of an $8\times 8$ qubit circuit with depth $40$ was previously beyond the reach of supercomputers. Our algorithm can compute this within $2$ minutes using a small portion ($\approx$ 14% of the nodes) of the cluster. Furthermore, by successfully simulating quantum supremacy circuits of size $9\times 9\times 40$, $10\times 10\times 35 $, $11\times 11\times 31$, and $12\times 12\times 27 $, we give evidence that noisy random circuits with realistic physical parameters may be simulated classically. This suggests that either harder circuits or error-correction may be vital for achieving quantum supremacy from random circuit sampling.