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arXiv · 2305.04954

A sharp phase transition in linear cross-entropy benchmarking

Brayden Ware·Abhinav Deshpande·Dominik Hangleiter·Pradeep Niroula·Bill Fefferman·Alexey V. Gorshkov·Michael J. Gullans
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Abstract

Demonstrations of quantum computational advantage and benchmarks of quantum processors via quantum random circuit sampling are based on evaluating the linear cross-entropy benchmark (XEB). A key question in the theory of XEB is whether it approximates the fidelity of the quantum state preparation. Previous works have shown that the XEB generically approximates the fidelity in a regime where the noise rate per qudit $\varepsilon$ satisfies $\varepsilon N \ll 1$ for a system of $N$ qudits and that this approximation breaks down at large noise rates. Here, we show that the breakdown of XEB as a fidelity proxy occurs as a sharp phase transition at a critical value of $\varepsilon N$ that depends on the circuit architecture and properties of the two-qubit gates, including in particular their entangling power. We study the phase transition using a mapping of average two-copy quantities to statistical mechanics models in random quantum circuit architectures with full or one-dimensional connectivity. We explain the phase transition behavior in terms of spectral properties of the transfer matrix of the statistical mechanics model and identify two-qubit gate sets that exhibit the largest noise robustness.

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Brayden Ware, Abhinav Deshpande, Dominik Hangleiter, Pradeep Niroula, Bill Fefferman, Alexey V. Gorshkov, Michael J. Gullans. 2023-05-08. A sharp phase transition in linear cross-entropy benchmarking. https://arxiv.org/abs/2305.04954

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