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.

We have demonstrated the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude faster than previously reported results. A classical channel at 1550 nm operates in parallel with a quantum channel at 845 nm. Clock recovery techniques on the classical channel at 1.25 Gbps enable quantum transmission at up to the clock rate. System performance is currently limited by the timing resolution of our silicon avalanche photodiode detectors. With improved detector resolution, our technique will yield another order of magnitude increase in performance, with existing technology.

We present a quantitative study of various limitations on quantum cryptographic systems operating with sifted-key rates over Mbit/s. The dead time of silicon APDs not only limits the sifted-key rate but also causes correlation between the neighboring key bits. In addition to the well-known count-rate dependent timing jitter in avalanche photo-diode (APD), the faint laser sources, the vertical cavity surface emission lasers (VCSELs) in our system, also induce a significant amount of data-dependent timing jitter. Both the dead time and the data-dependent timing jitter are major limiting factors in designing QKD systems with sifted-key rates beyond Mbit/s.

We previously demonstrated a high speed, point to point, quantum key distribution (QKD) system with polarization coding over a fiber link, in which the resulting cryptographic keys were used for one-time pad encryption of real time video signals. In this work, we extend the technology to a three-node active QKD network -one Alice and two Bobs. A QKD network allows multiple users to generate and share secure quantum keys. In comparison with a passive QKD network, nodes in an active network can actively select a destination as a communication partner and therefore, its sifted-key rate can remain at a speed almost as high as that in the point-to-point QKD. We demonstrate our three-node QKD network in the context of a QKD secured real-time video surveillance system. In principle, the technologies for the three-node network are extendable to multi-node networks easily. In this paper, we report our experiments, including the techniques for timing alignment and polarization recovery during switching, and discuss the network architecture and its expandability to multi-node networks.

NIST has developed a high-speed quantum key distribution (QKD) test bed incorporating both free-space and fiber systems. These systems demonstrate a major increase in the attainable rate of QKD systems: over two orders of magnitude faster than other systems. NIST's approach to high-speed QKD is based on a synchronous model with hardware support. Practical one-time pad encryption requires high key generation rates since one bit of key is needed for each bit of data to be encrypted. A one-time pad encrypted surveillance video application was developed and serves as a demonstration of the speed, robustness and sustainability of the NIST QKD systems. We discuss our infrastructure, both hardware and software, its operation and performance along with our migration to quantum networks.