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IEEE Photonics Technology Letters

Experimental investigation of the performance limits for first telecommunications-window quantum cryptography systems

Paul D. Townsend

Published Jul 1, 1998• 82 citations
Publisher

Abstract

Quantum cryptography offers the unique possibility of certifiably secure key distribution between remote locations, practical systems require efficient, low noise, single photon avalanche photodiodes (SPADs) to achieve this goal. This letter reports experimental results from a polarization-encoded system utilizing a state-of-the-art silicon SPAD. The system is used to investigate the performance limits of quantum cryptography systems operating in the first optical fiber communication window at wavelengths around 0.8 μm. The results demonstrate the potential for secure quantum key distribution at Mb/spl middot/s1rates over fiber LANs also carrying conventional high-speed (Gb/spl middot/s1) data channels at a wavelength of 1.3 μm.

DOI
10.1109/68.681313

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Oct 18, 2006•1 citation
Quantum cryptography offers the unique possibility of certifiably secure key distribution between remote locations, practical systems require efficient, low noise, single photon avalanche photodiodes (SPADs) to achieve this goal. This letter reports experimental results from a polarization-encoded system utilizing a state-of-the-art silicon SPAD. The system is used to investigate the performance limits of quantum cryptography systems operating in the first optical fiber communication window at wavelengths around 0.8 μm. The results demonstrate the potential for secure quantum key distribution at Mb/spl middot/s1rates over fiber LANs also carrying conventional high-speed (Gb/spl middot/s1) data channels at a wavelength of 1.3 μm.
Quantum cryptography systems can operate over relatively long distances in standard telecommunications fiber by taking advantage of the low transmission losses in these fibers at 1.3 or 1.5 microns. Although there has been much progress toward the development of highly efficient and low-noise detectors for these wavelengths, silicon avalanche photodiodes currently offer superior single photon counting performance, but only at visible and near IR wavelengths where the fiber transmission is poor. For ranges typical of local area networks, it is possible that a quantum key distribution (QKD) system operating below 850nm could be optimal, even though standard telecommunications fiber supports multiple optical modes at these wavelengths. We have recently developed an optical mode filter that allows efficient higher order mode rejection from standard telecommunications fiber near 830nm. We have used this type of filter to launch and recover QKD signals from a polarization-based system implementing the BB84 quantum cryptography protocol. Here we present results from testing and operation in installed fiber links ranging up to 3km. These results demonstrate that the filters can attenuate the higher order modes over 35dB while having a minimal (<1dB) impact on the fundamental mode carrying the QKD signal.
We have developed a system for quantum key distribution (QKD), based on standard telecommunication lasers, detectors, and optical fiber, that passively compensates for time-dependent variations of the fiber-optic path due to stress, temperature changes, or birefringence. This approach allows information encoded in phase shifts imposed on single-photon-level pulses to be accurately read out after transmission over many kilometers of uncontrolled fiber. Cooled InGaAs avalanche photodiodes, pulse-biased using a special noise canceling circuit, are used to detect single 1.31-/spl mu/m infrared photons with a high efficiency, low dark-count rate, and subnanosecond time resolution. A single optical fiber carries both the quantum information and precise 1.55 /spl mu/m timing pulses between the two end stations. Overall synchronization of end-station activities, public discussion of basis choices, error correction, and privacy amplification have all been implemented over a local area network (LAN). The system at present generates raw, error-corrected, and privacy-amplified key data at rates of /spl sim/1000, 600, and 200 bits/s, respectively, over a 10-km single-mode fiber link.
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 today's 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.
ABSTRACT Quantum Cryptography has demonstrated the potential for ultra-secure communications. However, with quantum-channel transmission rates in the MHz range, typical link losses and signal-to-noise ratios have resulted in key-production rates that are impractical for continuous one-time-pad encryption of high-bandwidth communications. We have developed high-speed data handling electronics that support quantum-channel transmission rates up to 1.25 GHz. This system has demonstrated error-corrected and privacy-amplified key rates above 1 Mbps over a free-space link. While the transmission rate is ultimately limited by timi ng jitter in the single-photon avalanche photodiodes (SPADs), we find the timing resolution of silicon SPADs sufficient to operate efficiently with temporal gates as short as 100 ps. We have developed systems to implement such high-resolution gating in our system, and anticipate the attendant reduction in noise to produce significantly higher secret-key bitrates. Keywords: Single-photon detection, quantum key distribution, avalanche photodiode