Quantum System Identification

TL;DR

This paper develops a comprehensive framework for quantum system identification, enabling estimation of internal quantum processes from input-output data, and highlights how prior knowledge and measurement choices influence the identifiability of system parameters.

Contribution

It introduces a general classification framework for quantum system identification and provides criteria for parameter estimability based on experimental setups and prior knowledge.

Findings

Bell measurement can be more efficient for system identification.

The framework allows estimation of Hamiltonian coupling constants when system topology is known.

Prior knowledge enhances the ability to identify quantum system components.

Abstract

The aim of quantum system identification is to estimate the ingredients inside a black box, in which some quantum-mechanical unitary process takes place, by just looking at its input-output behavior. Here we establish a basic and general framework for quantum system identification, that allows us to classify how much knowledge about the quantum system is attainable, in principle, from a given experimental setup. Prior knowledge on some elements of the black box helps the system identification. We present an example in which a Bell measurement is more efficient to identify the system. When the topology of the system is known, the framework enables us to establish a general criterion for the estimability of the coupling constants in its Hamiltonian.