Optimal Calibration of Qubit Detuning and Crosstalk

TL;DR

This paper develops optimal strategies for calibrating qubit detuning and crosstalk, significantly reducing calibration time while maintaining high accuracy, validated through experiments on NV centers and superconducting transmons.

Contribution

It introduces Fisher information-based optimal calibration protocols for qubit detuning and crosstalk, improving efficiency and robustness over existing methods.

Findings

Optimal measurement protocols outperform traditional methods.

Experimental validation confirms up to 50% reduction in calibration time.

High-precision parameter estimation achieved with fewer measurements.

Abstract

Characterizing and calibrating physical qubits is essential for maintaining the performance of quantum processors. A key challenge in this process is the presence of crosstalk that complicates the estimation of individual qubit detunings. In this work, we derive optimal strategies for estimating detuning and crosstalk parameters by optimizing Ramsey interference experiments using Fisher information and the Cramer-Rao bound. We compare several calibration protocols, including measurements of a single quadrature at multiple times and of two quadratures at a single time, for a fixed number of total measurements. Our results predict that the latter approach yields the highest precision and robustness in both cases of isolated and coupled qubits. We validate experimentally our approach using a single NV center as well as superconducting transmons. Our approach enables accurate parameter extraction with significantly fewer measurements, resulting in up to a 50% reduction in calibration time while maintaining estimation accuracy.