A source of polarization-entangled photon pairs interfacing quantum memories with telecom photons

TL;DR

This paper introduces a polarization-entangled photon pair source optimized for long-distance quantum communication, matching the spectral properties of quantum memories and demonstrating high entanglement quality.

Contribution

The work presents a novel photon pair source with spectral filtering and active stabilization, tailored for quantum memories, with an accurate theoretical model and high entanglement fidelity.

Findings

Photon pairs at 883 nm and 1338 nm with 240 MHz bandwidth produced

High entanglement visibility of 96.1% achieved in Bell test

Spectral filtering and stabilization improve quantum memory compatibility

Abstract

We present a source of polarization-entangled photon pairs suitable for the implementation of long-distance quantum communication protocols using quantum memories. Photon pairs with wavelengths 883 nm and 1338 nm are produced by coherently pumping two periodically poled nonlinear waveguides embedded in the arms of a polarization interferometer. Subsequent spectral filtering reduces the bandwidth of the photons to 240 MHz. The bandwidth is well-matched to a quantum memory based on an Nd:YSO crystal, to which, in addition, the center frequency of the 883 nm photons is actively stabilized. A theoretical model that includes the effect of the filtering is presented and accurately fits the measured correlation functions of the generated photons. The model can also be used as a way to properly assess the properties of the source. The quality of the entanglement is revealed by a visibility of V = 96.1(9)% in a Bell-type experiment and through the violation of a Bell inequality.