# Characterization of entangling properties of quantum measurement via two-mode quantum detector tomography using coherent state probes

## TL;DR

This paper introduces a new entanglement measure for multi-mode quantum detectors, demonstrated through tomography of superconducting nanowire detectors using coherent states, revealing their entangling capabilities.

## Contribution

It proposes a novel entanglement measure for quantum detectors and demonstrates its application via two-mode detector tomography with coherent state probes.

## Key findings

- The detector can exhibit entangled measurement properties under certain conditions.
- Coherent states are sufficient for characterizing the entangling capabilities of the detector.
- The measure helps verify and understand the entangling properties of quantum detectors.

## Abstract

Entangled measurement is a crucial tool in quantum technology. We propose a new entanglement measure of multi-mode detection, which estimates the amount of entanglement that can be created in a measurement. To illustrate the proposed measure, we perform quantum tomography of a two-mode detector that is comprised of two superconducting nanowire single photon detectors. Our method utilizes coherent states as probe states, which can be easily prepared with accuracy. Our work shows that a separable state such as a coherent state is enough to characterize a potentially entangled detector. We investigate the entangling capability of the detector in various settings. Our proposed measure verifies that the detector makes an entangled measurement under certain conditions, and reveals the nature of the entangling properties of the detector. Since the precise characterization of a detector is essential for applications in quantum information technology, the experimental reconstruction of detector properties along with the proposed measure will be key features in future quantum information processing.