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.
High-Performance Quantum Frequency Conversion from Ultraviolet to Telecom Band
Hefei National Research Center for Physical Sciences at the Microscale（合肥微尺度物质科学国家研究中心）；School of Physical Sciences, University of Science and Technology of China（中国科学技术大学物理学院）；Jinan Institute of Quantum Technology（济南量子技术研究院）；CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学中国科学院量子信息与量子物理前沿卓越创新中心）；Hefei National Laboratory（合肥国家实验室）
