Experimental Bayesian estimation of quantum state preparation, measurement, and gate errors in multi-qubit devices

TL;DR

This paper presents a Bayesian approach for accurately estimating and mitigating errors in multi-qubit quantum devices, improving error characterization and correction methods for quantum computing.

Contribution

The paper introduces a Bayesian method for comprehensive error estimation in multi-qubit devices, including non-diagonal and coherent errors, with practical mitigation strategies.

Findings

Identified non-negligible coherent reset errors in superconducting qubits.

Demonstrated error mitigation via pre-rotations on qubits.

Achieved high-accuracy error parameter estimation with fewer measurements.

Abstract

We introduce a Bayesian method for the estimation of single qubit errors in quantum devices, and use it to characterize these errors on three 27-qubit superconducting qubit devices. We self-consistently estimate up to seven parameters of each qubit's state preparation, readout, and gate errors, analyze the stability of these errors as a function of time, and demonstrate easily implemented approaches for mitigating different errors before a quantum computation experiment. On the investigated devices we find non-negligible qubit reset errors that cannot be parametrized as a diagonal mixed state, but manifest as a coherent phase of a superposition with a small contribution from the qubit's excited state. We are able to mitigate such errors by applying pre-rotations on the initialized qubits, which we demonstrate with multi-qubit entangled states. Our results demonstrate that Bayesian estimation can resolve small parameters - including those pertaining to quantum gate errors - with a high relative accuracy, at a lower measurement cost as compared with standard characterization approaches.