We demonstrate an ultrabright narrow-band two-photon source at the 1.5 -\mu m telecom wavelength for long-distance quantum communication. By utilizing a bow-tie cavity, we obtain a cavity enhancement factor of 4.06×104. Our measurement of the second-order correlation function G(2)(τ) reveals that the linewidth of 2.4 MHz has been hitherto unachieved in the 1.5 -\mu m telecom band. This two-photon source is useful for obtaining a high absorption probability close to unity by quantum memories set inside quantum repeater nodes. Furthermore, to the best of our knowledge, the observed spectral brightness of 3.94×105 pairs/(s⋅MHz⋅mW) is also the highest reported over all wavelengths.
@article{arxiv.1803.07749,
title = {Ultrabright narrow-band telecom two-photon source for long-distance quantum communication},
author = {Kazuya Niizeki and Kohei Ikeda and Mingyang Zheng and Xiuping Xie and Kotaro Okamura and Nobuyuki Takei and Naoto Namekata and Shuichiro Inoue and Hideo Kosaka and Tomoyuki Horikiri},
journal= {arXiv preprint arXiv:1803.07749},
year = {2018}
}