Broadband-laser-diode pumped PPKTP-Sagnac polarization-entangled photon source

TL;DR

This paper presents a compact, stable, and low-cost polarization-entangled photon source at 810 nm using a broadband laser diode and a Sagnac-loop with PPKTP crystal, achieving high fidelity and visibility for quantum applications.

Contribution

It is the first to combine a multi-mode pump laser with a Sagnac-loop configuration for entangled photon generation.

Findings

Fidelities of 0.948 and 0.963 for Bell states achieved.

Polarization visibilities above 96.2%.

Bell inequality S value of 2.78.

Abstract

We experimentally demonstrate a polarization-entangled photon source at 810 nm using a type-II phase-matched PPKTP crystal pumped by a low-cost, broadband laser diode with a central wavelength of 405 nm and a typical bandwidth of 0.53 nm. The PPKTP crystal is placed in a Sagnac-loop to realize the compact size and high stability. The downconverted biphotons, the signal and the idler, have typical bandwidths of 5.57 nm and 7.32 nm. We prepare two Bell states |Psi+> and |Psi-> with the fidelities of 0.948+-0.004 and 0.963+-0.002. In polarization correlation measurement, the visibilities are all higher than 96.2%, and in the Bell inequality test, the S value can achieve 2.78+-0.01. To our knowledge, this experiment is the first to combine a multi-mode pump laser with a Sagnac-loop configuration. This high-quality and low-cost entangled photon source may have many practical applications in quantum information processing.