Abstract
We show that the performance of a 1310-nm quantum key distribution (QKD) system with up-conversion detectors pumped at 1550 nm is comparable with or better than that of current 1550-nm QKD systems with a pump at shorter wavelength. The nonlinearly-induced dark counts are reduced when the wavelength of the pump light is longer than that of the quantum signal. We have developed a 1550-nm pump up-conversion detector for a 1310-nm QKD system, and we experimentally study the polarization sensitivity, pump-signal format, and various influences on the dark count rate. Using this detector in a proof-of-principle experiment, we have achieved a secure key rate of 500 kbit/s at 10 km and 9.1 kbit/s at 50 km in a 625-MHz, B92, polarization-coding QKD system, and we expect that the system performance could be improved further.
Highlights
Quantum key distribution (QKD) was first introduced in 1984 [1]
We have shown that a 1306-nm QKD system with a 1550-nm pump up-conversion detector can yield better system performance, when the system is aimed at a high securekey rate over relatively short distances
We find that pulsing the pump light helps to reduce the dark count rate while the internal conversion efficiency remains close 100% as long as the pump pulse is sufficiently wider than the signal pulse
Summary
Quantum key distribution (QKD) was first introduced in 1984 [1]. Since that time both the speed and the distance of QKD systems have been greatly improved over both free space and fiber [2−5]. Superconducting single-photon detectors can operate in the free-running mode and their only limitation to the sifted-key rate is the dead time, usually below 10 ns [8, 9]. Sum frequency generation has been applied to up-convert photons from the lowloss fiber windows to wavelengths where they can be efficiently detected by Si-APDs. With periodically poled LiNbO3 (PPLN) conversion efficiencies can approach 100% [12], and this up-conversion technique was used by Takesue et al to demonstrate a QKD system with a secure key rate of approximately 200 bit/s over 100 km [13]. In most current QKD systems with up-conversion detectors, the quantum signal is transmitted at 1550 nm and the wavelength of the pump is shorter than the signal, for example 1310 nm [13] or 980 nm [14] The advantage of this scheme is that the fiber loss is minimal (0.2 dB/km) around 1550 nm. We observe a secure key rate of 9.1 kbit/s over 50 km of standard single-mode fiber
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