Fitting time-dependent Markovian dynamics to noisy quantum channels

TL;DR

This paper extends existing algorithms to characterize noisy quantum channels by analyzing time-dependent Markovian dynamics from a sequence of snapshots, enabling better diagnostics of quantum errors over short time scales.

Contribution

It introduces a method to analyze time-dependent Markovian quantum channels from experimental data, overcoming the previous assumption of time-independence.

Findings

Provides a diagnostic tool for time-dependent quantum noise

Extends the analysis framework to a broader class of quantum dynamics

Addresses a long-standing theoretical problem in quantum channel characterization

Abstract

Understanding how to characterise and mitigate errors is a key challenge in developing reliable quantum architecture for near-term applications. Recent work (arXiv:2103.17243) provides an efficient set of algorithms for analysing unknown noise processes requiring only tomographic snapshots of the quantum operator under consideration, without the need of any a-priori information on the noise model, nor necessitating a particular experimental setup. The only assumption made is that the observed channel can be approximated by a time-independent Markovian map, which is a typically reasonable framework when considering short time scales. In this note we lift the time-independent assumption, presenting an extension of the scheme now able to analyse noisy dynamics with time-dependent generators from a sequence of snapshots. We hence provide a diagnostic tool for a wider spectrum of instances while inheriting all the favourable features from the previous protocol. On the theoretical side, the problem of characterising time-dependent Markovian channels has been an open problem for many decades. This work gives an approach to tackle this characterisation problem rigorously.