Phase-stable source of polarization-entangled photons in a linear double-pass configuration

TL;DR

This paper presents a compact, efficient, and stable polarization-entangled photon source using a novel linear double-pass configuration with bi-directional pumping of a single ppKTP crystal, achieving high detection rates and fidelity.

Contribution

The authors introduce a new 'folded sandwich' linear configuration for entangled photon generation that enhances stability and efficiency over previous methods.

Findings

Achieved a detection rate of 11.8 kcps with 10.4 μW pump power.

Maintained a Bell-state fidelity of 99.3%.

Generated entangled photons at non-degenerate wavelengths 784 nm and 839 nm.

Abstract

We demonstrate a compact, robust, and highly efficient source of polarization-entangled photons, based on linear bi-directional down-conversion in a novel 'folded sandwich' configuration. Bi-directionally pumping a single periodically poled KTiOPO$_4$ (ppKTP) crystal with a 405-nm laser diode, we generate entangled photon pairs at the non-degenerate wavelengths 784 nm (signal) and 839 nm (idler), and achieve an unprecedented detection rate of 11.8 kcps for 10.4 $\mu$W of pump power (1.1 million pairs / mW), in a 2.9-nm bandwidth, while maintaining a very high two-photon entanglement quality, with a Bell-state fidelity of $99.3\pm0.3$%.