High-performance source of spectrally pure, polarization entangled photon pairs based on hybrid integrated-bulk optics

TL;DR

This paper introduces a hybrid integrated-bulk optics source of polarization-entangled photon pairs that achieves high fidelity, brightness, and efficiency simultaneously with low pump power.

Contribution

It presents a novel hybrid approach combining waveguiding and bulk optics to optimize all key metrics of entangled photon sources.

Findings

96% fidelity to the singlet state

82% Hong-Ou-Mandel interference visibility

High brightness of 2.9 million pairs per (mode·s·mW)

Abstract

Entangled photon pair sources based on bulk optics are approaching optimal design and implementation, with high state fidelities, spectral purities and heralding efficiencies, but generally low brightness. Integrated entanglement sources, while providing higher brightness and low-power operation, often sacrifice performance in output state quality and coupling efficiency. Here we present a polarization-entangled pair source based on a hybrid approach of waveguiding and bulk optics, addressing every metric simultaneously. We show 96% fidelity to the singlet state, 82% Hong-Ou-Mandel interference visibility, 43% average Klyshko efficiency, and a high brightness of $2.9\times10^6$ pairs/(mode$\cdot$s$\cdot$mW), while requiring only microwatts of pump power.