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Mitigating quantum gate errors for variational eigensolvers using hardware-inspired zero-noise extrapolation

A. Uvarov, D. Rabinovich, O. Lakhmanskaya, K. Lakhmanskiy, J. Biamonte, Soumik Adhikary

Physical Review A, 2023

9 citations

Abstract

Variational quantum algorithms have emerged as a cornerstone of contemporary quantum algorithms research. Practical implementations of these algorithms, despite offering certain levels of robustness against systematic errors, show a decline in performance due to the presence of stochastic errors and limited coherence time. In this work, we develop a recipe for mitigating quantum gate errors for variational algorithms using zero-noise extrapolation. We introduce an experimentally amenable method to control error strength in the circuit. We utilise the fact that gate errors in a physical quantum device are distributed inhomogeneously over different qubits and pairs thereof. As a result, one can achieve different circuit error sums based on the manner in which abstract qubits in the circuit are mapped to a physical device. We find that the estimated energy in the variational approach is approximately linear with respect to the circuit error sum (CES). Consequently, a linear fit through the energy-CES data, when extrapolated to zero CES, can approximate the energy estimated by a noiseless variational algorithm. We demonstrate this numerically and further prove that the approximation is exact if the two-qubit gates in the circuits are arranged in the form of a regular graph.

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