SUB-NANOSECOND GATING TO REDUCE QUANTUM BIT ERROR RATE IN HIGH-SPEED FREE-SPACE QUANTUM KEY DISTRIBUTION
Alessandro Restelli, Joshua C. Bienfang, Alan Mink, Barry J.† Hershman, Charles Clark, Carl J. Williams
For single-photon quantum key distribution (QKD) systems using free-space optical (FSO) links daylight is the dominant contributor to the quantum bit error rate (QBER).† Spatial and spectral filtering are effective techniques for reducing the solar-photon flux at the receiver, but to achieve QBERs low enough to support the distillation of secret key it is also necessary to use strong temporal gating.† The SNR improvement gained by temporal filtering is ultimately limited by the receiverís ability to anticipate the arrival time of the signal photons, and thus is dependant on the timing resolution of the single-photon detectors.† To date temporal gates of the order of 1 ns have been used in FSO QKD systems, partly due to the resolution of traditional Si single-photon avalanche photodiodes (SPADs).† The current availability of Si SPADs with timing jitter of the order of 50 ps supports the implementation of temporal gates shorter than 100 ps without significant signal loss, potentially reducing the daylight QBER by an order of magnitude. We have demonstrated techniques for implementing post-selection gating down to 50 ps and at repetition rates up to 1.25 GHz. We present the design and performance of such gates, and illustrate their benefit to the performance of FSO QKD links.
Name: Alessandro Restelli (not Sigma Xi member)
Mentorís name: Charles W. Clark
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