Barry Hershman

Quantum key distribution with 1.25 Gbps clock synchronization

Clock recovery techniques at 1.25 Gbps enable continuous quantum key distribution at demonstrated sifted-key rates up to 1.0 Mbps. This rate is two orders of magnitude faster than has been reported previously

1310-nm quantum key distribution system with up-conversion pump wavelength at 1550 nm

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.

Experimental study of high speed polarization-coding quantum key distribution with sifted-key rates over Mbit/s

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.

High-speed quantum key distribution system supports one-time pad encryption of real-time video

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. NISTs 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.

Programmable instrumentation and gigahertz signaling for single-photon quantum communication systems

We discuss custom time-tagging instrumentation for high-speed single-photon metrology, focusing particularly on implementations that can tag and process detection events from multiple single-photon detectors with sub-nanosecond timing resolution and at detection rates above 100 MHz. The systems we present view the detector signal as if it were a serial data stream, tagging events according to the bit period in which a rising edge from the detector occurs. We achieve sub-nanosecond resolution with serial data receivers operating up to 10 Gb s−1. Data processing bottlenecks are avoided with pipelined algorithms and controlled data flow implemented in field-programmable gate arrays.

A Quantum Network Manager that Supports a One-Time Pad Stream

We have begun to expand the NIST quantum key distribution (QKD) system into a quantum network to support secure cryptography. We are starting with a simple three-node network, one Alice switched between Bob1 and Bob2. To support such a quantum network, we have implemented a quantum network manager that not only handles the switch and QKD protocol startup operations but also handles multiplexing and synchronization of secret key streams. We describe the function, structure and interfaces of this quantum network manager and report on initial switching overhead. We also discuss some steps we plan to take to optimize that overhead as well as hide its latency for certain applications.

Demonstration of an active quantum key distribution network

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.

Free-Space Quantum Cryptography in the H-alpha Fraunhofer Window

Free-space Quantum key distribution (QKD) has shown the potential for the practical production of cryptographic key for ultra-secure communications. The performance of any QKD system is ultimately limited by the signal to noise ratio on the single-photon channel, and over most useful communications links the resulting key rates are impractical for performing continuous one-time-pad encryption of todays broadband communications. We have adapted clock and data recovery techniques from modern telecommunications practice, combined with a synchronous classical free-space optical communications link operating in parallel, to increase the repetition rate of a free-space QKD system by roughly 2 orders of magnitude over previous demonstrations. We have also designed the system to operate in the H-alpha Fraunhofer window at 656.28 nm, where the solar background is reduced by roughly 7 dB. This system takes advantage of high efficiency silicon single-photon avalanche photodiodes with <50ps timing resolution that are expected to enable operation at a repetition rate of 2.5 GHz. We have identified scalable solutions for delivering sustained one-time-pad encryption at 10 Mbps, thus making it possible to integrate quantum cryptography into first-generation Ethernet protocols.

High speed fiber-based quantum key distribution using polarization encoding

We have implemented a quantum key distribution (QKD) system with polarization encoding at 850 nm over 1 km of optical fiber. The high-speed management of the bit-stream, generation of random numbers and processing of the sifting algorithm are all handled by a pair of custom data handling circuit boards. As a complete system using a clock rate of 1.25 Gbit/s, it produces sifted keys at a rate of 1.1 Mb/s with an error rate lower than 1.3% while operating at a transmission rate of 312.5 Mbit/s and a mean photon number μ = 0.1. With a number of proposed improvements this system has a potential for a higher key rate without an elevated error rate.

Quantum Key Distribution System Operating at Sifted-Key Rate over 4 Mbit/s

A complete fiber-based polarization encoding quantum key distribution (QKD) system based on the BB84 protocol has been developed at National Institute of Standard and Technology (NIST). The system can be operated at a sifted key rate of more than 4 Mbit/s over optical fiber of length 1 km and mean photon number 0.1. The quantum channel uses 850 nm photons from attenuated high speed VCSELs and the classical channel uses 1550 nm light from normal commercial coarse wavelength division multiplexing devices. Sifted-key rates and quantum error rates at different transmission rates are measured as a function of distance (fiber length). A polarization auto-compensation module has been developed and utilized to recover the polarization state and to compensate for temporal drift. An automatic timing alignment device has also been developed to quickly handle the initial configuration of quantum channels so that detection events fall into the correct timing window. These automated functions make the system more practical for integration into existing optical local area networks.