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

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 x 10(4). Our measurement of the second-order correlation function G((2))(tau) reveals that the linewidth of 2.4MHz 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 x 10(5) pairs/(s.MHz.mW) is also the highest reported over all wavelengths. (c) 2018 The Japan Society of Applied Physics