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Japanese Journal of Applied Physics

10.5 km Fiber-Optic Quantum Key Distribution at 1550 nm with a Key Rate of 45 kHz

Akio Yoshizawa, Ryosaku Kaji, Hidemi Tsuchida

Published May 21, 2004• 29 citations
Publisher

Abstract

High-speed single-photon detectors are crucial for efficiently performing quantum key distribution. We demonstrate fiber-optic quantum key distribution at 1550 nm using single-photon detectors operating at 10 MHz. Discharge pulse counting is adopted for single-photon detection in order to suppress after-pulse generation. Furthermore, by setting a dead time in single-photon detection, we discard after-pulses to reduce the number of bit errors in the quantum key distribution. Using discharge pulse counting and after-pulse discarding in the quantum key distribution, we can achieve a key rate of 45 kHz with a bit-error rate of 2%. The fiber length is 10.5 km.

DOI
10.1143/jjap.43.l735

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High-speed single-photon detectors are crucial for efficiently performing quantum key distribution. We demonstrate fiber-optic quantum key distribution at 1550 nm using single-photon detectors operating at 10 MHz. Discharge pulse counting is adopted for single-photon detection in order to suppress after-pulse generation. Furthermore, by setting a dead time in single-photon detection, we discard after-pulses to reduce the number of bit errors in the quantum key distribution. Using discharge pulse counting and after-pulse discarding in the quantum key distribution, we can achieve a key rate of 45 kHz with a bit-error rate of 2%. The fiber length is 10.5 km.
This paper gives experimental results of quantum key distribution on a fiber-optic setup at a telecom wavelength of 1555 nm. A self-compensated two-channel optical circuit is used. Quantum key distribution was performed by coding the phase states of single photons radiated by a pulsed semiconductor laser in two alternative nonorthogonal bases. Specially developed single photon counters based on InGaAs: InP avalanche photodiodes were employed as high-sensitivity photodetectors. The results of investigation of the quantum efficiency, probability of afterpulses, and noise level for various operating modes of the detectors at temperatures from −40 to −60°C are given. A key distribution rate of 450 bit/s was obtained for a single-mode fiber-optic quantum communication channel between the receiver and sender 25 km long at a laser pulse clock frequency of 5 MHz and an average number of photons per pulse of about 0.2. For the achieved photodetector characteristics, the average number of errors in the quantum key did not exceed 3.7%.
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.
We report an entanglement-based quantum key distribution experiment that we performed over 100 km of optical fiber using a practical source and detectors. We used a silicon-based photon-pair source that generated high-purity time-bin entangled photons, and high-speed single photon detectors based on InGaAs/InP avalanche photodiodes with the sinusoidal gating technique. To calculate the secure key rate, we employed a security proof that validated the use of practical detectors. As a result, we confirmed the successful generation of sifted keys over 100 km of optical fiber with a key rate of 4.8 bit/s and an error rate of 9.1%, with which we can distill secure keys with a key rate of 0.15 bit/s.
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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.