A high-quality narrowband polarization-entangled source in the telecom band is preferred to avoid frequency dispersion for long-distance transmission in optical fibers and to efficiently couple with telecom band quantum memories. Here, we report narrowband, telecom-band, polarization-entangled photon pair generation based on the superposition of single-longitudinal-mode photon pairs from two monolithic nonlinear crystal cavities in a passively stable interferometer based on beam displacers. The photon pairs generated from the cavities exhibit a high coincidence to accidental coincidence ratio of 20000 and a bandwidth below 500 MHz. Two-photon polarization interference, Bell-inequality, and quantum state tomography are performed to indicate the high quality of the entangled source. The current configuration demonstrates greater stability than traditional free space cavity-enhanced polarization-entangled state generation, which is promising for quantum communication applications.
@article{arxiv.2402.18802,
title = {Narrowband telecom band polarization-entangled photon source by superposed monolithic cavities},
author = {Ming-Yuan Gao and Yin-Hai Li and Yan Li and Zhenghe Zhou and Guang-Can Guo and Zhi-Yuan Zhou and Bao-Sen Shi},
journal= {arXiv preprint arXiv:2402.18802},
year = {2024}
}