Directly Characterizing the Coherence of Quantum Detectors by Sequential Measurement

TL;DR

This paper introduces a new method to directly characterize quantum measurement properties by sequentially measuring non-compatible observables, avoiding full tomography and enabling efficient analysis of measurement coherence.

Contribution

The authors propose a general framework for directly measuring individual matrix entries of quantum measurement operators through sequential measurements, simplifying quantum property characterization.

Findings

Successfully implemented experimentally to monitor measurement coherence.

Demonstrated the feasibility of the protocol for arbitrary quantum measurements.

Showed accurate extraction of off-diagonal matrix entries.

Abstract

The quantum properties of quantum measurements are indispensable resources in quantum information processing and have drawn extensive research interest. The conventional approach to reveal the quantum properties relies on the reconstruction of the entire measurement operators by quantum detector tomography. However, many specific properties can be determined by a part of matrix entries of the measurement operators, which provides us the possibility to simplify the process of property characterization. Here, we propose a general framework to directly obtain individual matrix entries of the measurement operators by sequentially measuring two non-compatible observables. This method allows us to circumvent the complete tomography of the quantum measurement and extract the useful information for our purpose. We experimentally implement this scheme to monitor the coherent evolution of a general quantum measurement by determining the off-diagonal matrix entries. The investigation of the measurement precision indicates the good feasibility of our protocol to the arbitrary quantum measurements. Our results pave the way for revealing the quantum properties of quantum measurements by selectively determining the matrix entries of the measurement operators.