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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

High speed fiber-based quantum key distribution using polarization encoding

Xiao Hong Tang, Lijun Ma, Alan Mink, Anastase Nakassis, Barry Hershman, Joshua C. Bienfang, Ronald F. Boisvert, Charles W. Clark, Carl J. Williams

Published Aug 18, 2005• 15 citations
Publisher

Abstract

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.

DOI
10.1117/12.614598

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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.
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.
A novel, user-friendly quantum key distribution (QKD) system operating at a wavelength of 1550nm and at a clock rate of 10MHz was constructed to explore the compatibility of this emerging technology with the optical fiber network environment. Custom circuit boards providing the low-level control and sensing functions for both the transmitter and receiver were developed, allowing software-based system reconfiguration via USB interface to personal computers. The computer control allowed the user to change operating parameters such as detector bias voltages and pulse delays and also allowed for self-tuning of the system. Epitaxx avalanche photodiodes, operated in Geiger mode, were used to detect the single photons. A complete QKD protocol stack incorporating the sifting, reconciliation, privacy amplification, authentication and key confirmation functions was implemented in software. The system was tested over twenty five kilometers of dark underground fiber, producing 18.6 million sifted bits, with a sifted bit error rate of 4.9% at an average number of photons per pulse of 0.2, during a continuous 12-hour period of self-sustaining operation: a small portion of the secret bits distilled from each session's sifted bits were used to authenticate the next session. A total of 6.8 million shared secret bits were produced.
The National Institute of Standards and Technology (NIST) has developed a number of complete fiber-based high-speed quantum key distribution (QKD) systems that includes an 850 nm QKD system for a local area network (LAN), a 1310 nm QKD system for a metropolitan area network (MAN), and a 3-node quantum network controlled by a network manager. This paper discusses the key techniques used to implement these systems, which include polarization recovery, noise reduction, frequency up-conversion detection based on a periodically polled lithium nitrate (PPLN) waveguide, custom high-speed data handling boards and quantum network management. Using our quantum network, a QKD secured video surveillance application has been demonstrated. Our intention is to show the feasibility and sophistication of QKD systems based on current technology.
A quantum key distribution (QKD) system has been developed, using a standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz. The QKD system implements a polarization encoded version of the B92 protocol. The system employs vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, and silicon single photon avalanche diodes as the single photon detectors. A distributed feedback laser of emission wavelength 1.3 /spl mu/m, and a linear gain germanium avalanche photodiode was used to optically synchronize individual photons over the standard telecommunications fiber. The QKD system exhibited a quantum bit error rate (QBER) of 1.4%, and an estimated net bit rate (NBR) greater than 100 000 bits/sup -1/ for a 4.2-km transmission range. For a 10-km fiber range, a QBER of 2.1%, and an estimated NBR of greater than 7000 bits/sup -1/ was achieved.
In recent years quantum information research has lead to the discovery of a number of remarkable new paradigms for information processing and communication. These developments include quantum cryptography schemes that offer unconditionally secure information transport guaranteed by quantum-mechanical laws. Such potentially disruptive security technologies could be of high strategic and economic value in the future. Two major issues confronting researchers in this field are the transmission range (typically <100km) and the key exchange rate, which can be as low as a few bits per second at long optical fiber distances. This paper describes further research of an approach to significantly enhance the key exchange rate in an optical fiber system at distances in the range of 1-20km. We will present results on a number of application scenarios, including point-to-point links and multi-user networks. Quantum key distribution systems have been developed, which use standard telecommunications optical fiber, and which are capable of operating at clock rates of up to 2GHz. They implement a polarization-encoded version of the B92 protocol and employ vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, as well as silicon single-photon avalanche diodes as the single photon detectors. The point-to-point quantum key distribution system exhibited a quantum bit error rate of 1.4%, and an estimated net bit rate greater than 100,000 bits-1 for a 4.2 km transmission range.
We report the first quantum-key-distribution (QKD) systems capable of delivering sustainable, real-time secure keys continuously at rates exceeding 10 Mb/s. To achieve such rates, we developed high-speed postprocessing modules, achieving maximum data throughputs of 60 MC/s, 55 Mb/s, and 108 Mb/s for standalone operation of sifting, error correction, and privacy amplification modules, respectively. The photonic layer of the QKD systems features high-speed single-photon detectors based on self-differencing InGaAs avalanche photodiodes, phase encoding using an asymmetric Mach-Zehnder interferometer, and active stabilization of the interferometer phase and photon polarization. An efficient variant of the decoy-state BB84 protocol is implemented for the security analysis, with a large dataset size of 108bits selected to mitigate finite-size effects. Over a 2-dB channel, a record secure key rate of 13.72 Mb/s has been achieved averaged over 4.4 days of operation. We confirm the robustness and long-term stability on a second QKD system continuously running for 1 month without any user invention.