Measuring Quantum Correlations using Lossy Photon-Number-Resolving Detectors with Saturation

TL;DR

This paper analyzes how lossy, saturating photon-number-resolving detectors affect the measurement of quantum correlations via variance of difference of photocounts, providing analytic models and calibration insights.

Contribution

It derives an analytic expression for VDPs considering detector loss and saturation, and identifies the regime where VDPs remains a reliable quantum correlation measure.

Findings

VDPs are unreliable as an entanglement measure in the nonlinear detector regime.

The paper quantifies the linear response range of saturated detectors.

Provides a calibration method for detector quantum efficiency.

Abstract

The variance of difference of photocounts (VDPs) is an established measure of quantum correlations for quantum states of light. It enables us to discriminate between the classical correlation of a two-mode coherent state and the quantum correlation of a twin-beam state. We study the effect of loss and saturation of the photon-number-resolving detector on the measurement of the VDPs. An analytic function is derived for this variance, both for the coherent and the twin-beam states. It is found that the VDPs is no longer a reliable entanglement measure in the nonlinear regime of the detector response but it remains useful in some range of values of average photon numbers of the incident light. We also quantify the linear regime of the detector with saturation which will be useful for calibration of the detector quantum efficiency.