Efficient estimation of resonant coupling between quantum systems

TL;DR

This paper introduces a rapid, adaptive measurement method for precisely estimating the coupling strength and resonant frequency between two quantum systems, significantly reducing measurement shots needed compared to traditional approaches.

Contribution

The authors develop an adaptive algorithm that efficiently estimates coupling parameters in quantum systems with high precision and robustness against noise, outperforming standard methods.

Findings

Error in estimates decreases exponentially with measurement shots

High-precision estimates achieved in a few hundred shots

Method robust against relaxation and typical noise

Abstract

We present an efficient method for the characterization of two coupled discrete quantum systems, one of which can be controlled and measured. For two systems with transition frequencies $\omega_q$, $\omega_r$, and coupling strength $g$ we show how to obtain estimates of $g$ and $\omega_r$ whose error decreases exponentially in the number of measurement shots rather than as a power law expected in simple approaches. Our algorithm can thereby identify $g$ and $\omega_r$ simultaneously with high precision in a few hundred measurement shots. This is achieved by adapting measurement settings upon data as it is collected. We also introduce a method to eliminate erroneous estimates with small overhead. Our algorithm is robust against the presence of relaxation and typical noise. Our results are applicable to many candidate technologies for quantum computation, in particular, for the characterization of spurious two-level systems in superconducting qubits or stripline resonators.