Parameters estimation by fitting correlation functions of continuous quantum measurement

TL;DR

The paper introduces a practical method for estimating parameters of continuously measured quantum systems by fitting correlation functions, demonstrated through simulations and applicable to complex systems with experimental constraints.

Contribution

It presents a novel, versatile approach for parameter estimation in quantum systems that is practical, interpretable, and suitable for large Hilbert spaces and real experimental conditions.

Findings

Successfully applied to toy models and superconducting circuits

Handles multiple parameters simultaneously with experimental imperfections

Provides a direct, interpretable estimation process

Abstract

We propose a simple method to estimate the parameters of a continuously measured quantum system, by fitting correlation functions of the measured signal. We demonstrate the approach in simulation, both on toy examples and on a recent superconducting circuits experiment which proved particularly difficult to characterise using conventional methods. The idea is applicable to any system whose evolution is described by a jump or diffusive stochastic master equation. It allows the simultaneous estimation of many parameters, is practical for everyday use, is suitable for large Hilbert space dimensions, and takes into account experimental constraints such as detector imperfections and signal filtering and digitisation. Unlike existing methods, it also provides a direct way to understand how each parameter is estimated from the measured signal. This makes the approach interpretable, facilitates debugging, and enables validating the adequacy of a model with the observed data.