CW-pumped telecom band polarization entangled photon pair generation in a Sagnac interferometer

TL;DR

This paper presents a high-quality, tunable polarization entangled photon pair source at telecom wavelength using a Sagnac interferometer, suitable for long-distance quantum networks.

Contribution

It demonstrates a CW-pumped, degenerate 1550 nm entangled photon source with broad tunability and verified high entanglement quality, advancing quantum communication technologies.

Findings

Photon bandwidth of 2.4 nm measured

High entanglement quality confirmed by Bell tests

Photon wavelength tunable via crystal temperature and pump power

Abstract

A polarization entangled photon pair source is widely used in many quantum information processing applications such as teleportation, quantum swapping, quantum computation and high precision quantum metrology. Here, we report on the generation of a continuous-wave pumped degenerated 1550 nm polarization entangled photon pair source at telecom wavelength using a type-II phase-matched periodically poled KTiOPO4 crystal in a Sagnac interferometer. Hong-Ou-Mandel-type interference measurement shows the photon bandwidth of 2.4 nm. High quality of entanglement is verified by various kinds of measurements, for example two-photon interference fringes, Bell inequality and quantum states tomography. The wavelength of photons can be tuned over a broad range by changing the temperature of crystal or pump power without losing the quality of entanglement. This source will be useful for building up long-distance quantum networks.