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Frontiers in Optics

Quantum key distribution with 1.25 Gbps clock synchronization

Joshua C. Bienfang, Alex J. Gross, Alan Mink, Anastase Nakassis, Xiao Hong Tang, Charles W. Clark, Carl J. Williams, E. W. Hagley, Jesse Wen

Published Jan 1, 2004• 10 citations
Publisher

Abstract

Clock recovery techniques at 1.25 Gbps enable continuous quantum key distribution at demonstrated sifted-key rates exceeding 1 Mbps. This rate is two orders of magnitude faster than has been reported previously, and serves to enhance both the data encryption capabilities and the distance over which a QKD system can operate. Full-text article is not available.

DOI
10.1364/fio.2004.jtua2

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Quantum key distribution with 1.25 Gbps clock synchronization

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Quantum key distribution with 1.25 Gbps clock synchronization

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We have demonstrated the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude faster than previously reported results.A classical channel at 1550 nm operates in parallel with a quantum channel at 845 nm.Clock recovery techniques on the classical channel at 1.25 Gbps enable quantum transmission at up to the clock rate.System performance is currently limited by the timing resolution of our silicon avalanche photodiode detectors.With improved detector resolution, our technique will yield another order of magnitude increase in performance, with existing technology.This work was performed for the U.S.

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Comment on "Quantum key distribution with 1.25 Gbps clock synchronization" by J.C. Bienfang et al., quant-ph/0405097

Richard Hughes, J. E. Nordholt

We analyze the significance for quantum key distribution (QKD) of free-space quantum communications results reported in a recent paper (J. C. Bienfang et al., quant-ph/0405097, hereafter referred to as "Bienfang et al."), who contrast the quantum communications rate of their partial QKD implementation (which does not produce cryptographically useful shared, secret keys) over a short transmission distance, with the secret bit rates of previous full QKD implementations over much longer distances. We show that when a cryptographically relevant comparison with previous results is made, the system described by Bienfang et al. would offer no advantages for QKD, contrary to assertions in their paper and in spite of its high clock rate. Further, we show that the claim made by Bienfang et al. that "high transmission rates serve ... to extend the distance over which a QKD system can operate" is incorrect. Our analysis illustrates an important aspect of QKD that is too often overlooked in experiments: the sifted bit rate can be a highly misleading indicator of the performance of a QKD system.

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arXiv:0805.2193•Optics Express•Jul 14, 2008•120 citations
Clock recovery techniques at 1.25 Gbps enable continuous quantum key distribution at demonstrated sifted-key rates exceeding 1 Mbps. This rate is two orders of magnitude faster than has been reported previously, and serves to enhance both the data encryption capabilities and the distance over which a QKD system can operate. Full-text article is not available.
We have demonstrated the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude faster than previously reported results. A classical channel at 1550 nm operates in parallel with a quantum channel at 845 nm. Clock recovery techniques on the classical channel at 1.25 Gbps enable quantum transmission at up to the clock rate. System performance is currently limited by the timing resolution of our silicon avalanche photodiode detectors. With improved detector resolution, our technique will yield another order of magnitude increase in performance, with existing technology.
We have demonstrated the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude faster than previously reported results.A classical channel at 1550 nm operates in parallel with a quantum channel at 845 nm.Clock recovery techniques on the classical channel at 1.25 Gbps enable quantum transmission at up to the clock rate.System performance is currently limited by the timing resolution of our silicon avalanche photodiode detectors.With improved detector resolution, our technique will yield another order of magnitude increase in performance, with existing technology.This work was performed for the U.S.
We analyze the significance for quantum key distribution (QKD) of free-space quantum communications results reported in a recent paper (J. C. Bienfang et al., quant-ph/0405097, hereafter referred to as "Bienfang et al."), who contrast the quantum communications rate of their partial QKD implementation (which does not produce cryptographically useful shared, secret keys) over a short transmission distance, with the secret bit rates of previous full QKD implementations over much longer distances. We show that when a cryptographically relevant comparison with previous results is made, the system described by Bienfang et al. would offer no advantages for QKD, contrary to assertions in their paper and in spite of its high clock rate. Further, we show that the claim made by Bienfang et al. that "high transmission rates serve ... to extend the distance over which a QKD system can operate" is incorrect. Our analysis illustrates an important aspect of QKD that is too often overlooked in experiments: the sifted bit rate can be a highly misleading indicator of the performance of a QKD system.
Clock synchronization serves as a foundational subsystem in quantum key distribution (QKD). The recently proposed Qubit-based synchronization (Qubit4Sync) has opportunities in eliminating additional cost, noise, and potential side channels. It offers a promising alternative to dedicated synchronization hardware. However, the current frequency recovery process in Qubit4Sync requires high data throughput and computational speed, limiting practical use. To overcome these issues, we developed a fast frequency recovery algorithm that increases the recovery rate by orders of magnitude and remains robust under bad signal-to-noise ratio (SNR). This enables Qubit4Sync to operate effectively in mainstream gated-mode QKD systems. We further establish a theoretical model for frequency recovery, showing that our algorithm is robust against disturbances like dead time, jitter, and afterpulse. A frequency-domain SNR calculation method is also provided to guide parameter design for specific experimental conditions. This work opens the door to practical Qubit4Sync deployment in general QKD systems.
We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78- 0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.