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    Ultrabright narrow-band telecom two-photon source for long-distance quantum communication

    Kazuya Niizeki, Kohei Ikeda, Mingyang Zheng, Xiuping Xie, Kotaro Okamura, Nobuyuki Takei, Naoto Namekata, Shuichiro Inoue, Hideo Kosaka, and Tomoyuki Horikiri

    Applied Physics Express, 11, 042801 (2018).

    • Photon source

    We demonstrate an ultrabright narrow-band two-photon source at the 1.5 μm 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 μm 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.