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European Conference on Optical Communication

Performance limits for first telecommunications window quantum cryptography systems

Paul D. Townsend

Published Jan 1, 1997• 0 citations
Publisher

Abstract

We investigate the performance limits for quantum cryptography systems operating in the first telecommunications window using a prototype polarisation-encoded system operating at 830 nm. The potential for secure quantum key distribution at Mbit/s rates over fibre carrying a conventional high-speed (Gbit/s) data channel at 1300 nm is demonstrated.

DOI
10.1049/cp:19971465

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We investigate the performance limits for quantum cryptography systems operating in the first telecommunications window using a prototype polarisation-encoded system operating at 830 nm. The potential for secure quantum key distribution at Mbit/s rates over fibre carrying a conventional high-speed (Gbit/s) data channel at 1300 nm is demonstrated.
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.
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.
Top-performance sources of photonic entanglement are an indispensable resource for many applications in quantum communication, most notably quantum key distribution. However, up to now, no source has been shown to simultaneously exhibit the high pair-creation rate, broad bandwidth, excellent state fidelity, and low intrinsic loss necessary for gigabit secure key rates. In this work, we present for the first time a source of polarization-entangled photon pairs at telecommunication wavelengths that covers all these needs of real-world quantum-cryptographic applications, thus enabling unprecedented quantum-secure key rates of more than 1 Gbit/s. Our source is designed to optimally exploit state-of-the-art telecommunication equipment and detection systems. Any technological improvement of the latter would result in an even higher rate without modification of the source. We discuss the used wavelength-multiplexing approach, including its potential for multi-user quantum networks and its fundamental limitations. Our source paves the way for high-speed quantum encryption approaching present-day internet bandwidth.
Securing information in communication networks is an important challenge in today's world. Quantum Key Distribution (QKD) can provide unique capabilities towards achieving this security, allowing intrusions to be detected and information leakage avoided. We report here a record high bit rate prototype QKD system providing a total of 878 Gbit of secure key data over a 34 day period corresponding to a sustained key rate of around 300 kbit/s. The system was deployed over a standard 45 km link of an installed metropolitan telecommunication fibre network in central Tokyo. The prototype QKD system is compact, robust and automatically stabilised, enabling key distribution during diverse weather conditions. The security analysis includes an efficient protocol, finite key size effects and decoy states, with a quantified key failure probability of ε = 10⁻¹⁰.
Quantum cryptography has been proven to be the only practical method for fast distribution of secret keys needed for encryption. It enables absolutely secure information transfer from one party to another and allows for the detection of an eavesdropper without sacrificing security. This project involved designing and building a quantum cryptography device. This device has applications in many fields, including internet security as well as military communications. The data are encoded on single photons, which are sent through free space over a distance of about 30 cm. The electronics, which control the device however, are equally suitable for operation with fibre optic cables. The device was designed to operate in dark conditions within a laboratory. Currently, no research group has demonstrated transmission speeds faster than 8 kb/s. The aim of this project was to achieve bit rates faster than 10 kb/s, while operating under strict economic constraints. Although quantum cryptography was not demonstrated in the laboratory due to problems with the detector, the emission end, which generates single photons of light with one of two different polarisations, was shown to work as it was designed. The current design has limited commercial future due to the dark conditions under which the communication must take place. The project however has demonstrated that quantum cryptography is getting closer to becoming a reality.