Detector entanglement: Quasidistributions for Bell-state measurements

TL;DR

This paper introduces a method to analyze the entanglement properties of quantum measurement devices, specifically Bell-state detectors, by reconstructing quasidistributions that reveal nonlocal quantum coherence through negative values.

Contribution

We develop a novel approach to determine nonlocal quantum coherence in measurement devices using quasidistributions, and demonstrate its application to experimental Bell-state detectors.

Findings

Reconstructed entanglement quasidistributions from experimental data.

Detected negativities indicating quantum entanglement in measurement devices.

Validated the method by comparing experimental negativities with theoretical expectations.

Abstract

Measurements in the quantum domain can exceed classical notions. This concerns fundamental questions about the nature of the measurement process itself, as well as applications, such as their function as building blocks of quantum information processing protocols. In this paper we explore the notion of entanglement for detection devices in theory and experiment. A method is devised that allows one to determine nonlocal quantum coherence of positive-operator-valued measures via negative contributions in a joint distribution that fully describes the measurement apparatus under study. This approach is then applied to experimental data for detectors that ideally project onto Bell states. In particular, we describe the reconstruction of the aforementioned entanglement quasidistributions from raw data and compare the resulting negativities with those expected from theory. Therefore, our method provides a versatile toolbox for analyzing measurements regarding their quantum-correlation features for quantum science and quantum technology.