Effects of multiple pairs on visibility measurements of entangled photons generated by spontaneous parametric processes

TL;DR

This paper analyzes how multiple entangled photon pairs affect the visibility of two-photon interference, providing formulas that account for multi-pair emissions and showing indistinguishable pairs yield better visibility.

Contribution

It introduces formulas for TPI visibility considering multi-pair emissions and compares distinguishable and indistinguishable entangled pairs.

Findings

Indistinguishable entangled pairs offer higher visibility than distinguishable ones.

Formulas approximate TPI visibility as a function of average pair number for low collection efficiency.

High-order multi-pair emissions significantly impact the visibility measurements.

Abstract

Entangled photon-pair sources based on spontaneous parametric processes are widely used in photonic quantum information experiments. In this paper, we clarify the relationship between average photon-pair number and the visibility of two-photon interference (TPI) using those entanglement sources. We consider sources that generate distinguishable and indistinguishable entangled photon pairs, assuming coincidence measurements that use threshold detectors. We present formulas for the TPI visibility of a polarization entanglement that take account of all the high-order multi-pair emission events. Moreover, we show that the formulas can be approximated with simple functions of the average pair number when the photon collection efficiency is small. As a result, we reveal that an indistinguishable entangled pair provides better visibility than a distinguishable one.