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arXiv:0909.5519 · Optics Letters

Non-Poissonian statistics from Poissonian light sources with application to passive decoy state quantum key distribution

Marcos Curty, Tobias Moroder, Xiongfeng Ma, Norbert Lütkenhaus

Published Oct 14, 2009• 63 citations
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Abstract

We propose a method to prepare different non-Poissonian signal pulses from sources of Poissonian photon number distribution, using only linear optical elements and threshold photon detectors. This method allows a simple passive preparation of decoy states for quantum key distribution. We show that the resulting key rates are comparable with the performance of active choices of intensities of Poissonian signals.

DOI
10.1364/ol.34.003238

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We propose a method to prepare different non-Poissonian signal pulses from sources of Poissonian photon number distribution, using only linear optical elements and threshold photon detectors. This method allows a simple passive preparation of decoy states for quantum key distribution. We show that the resulting key rates are comparable with the performance of active choices of intensities of Poissonian signals.
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The decoy-state method and the non-orthogonal encoding protocol, being capable of resisting the photon-number splitting attack, have become attractive recently. Here, we combine both the methods and propose a new protocol using a conditionally prepared down-conversion source, following Poisson photon number distribution. In the protocol, Alice randomly changes the intensities of the pump light so that the intensity of signal photon of photon pair is randomly changed. The signal state is used for generating keys, the decoy states for detecting the eavesdropping and estimating the fraction of single-photon and two-photon pulses. We have simulated the final key rate over transmission distance, showing our scheme can enhance the performance of quantum key distribution.
We study the behavior of decoy-state quantum key distribution systems using a conditionally prepared down-conversion source, analyzing such a source running in a mode of operation with either a thermal photon number distribution or a Poisson photon number distribution. By comparing both modes of operations to the three-intensity proposal of Wang et al., to the one-intensity proposal of Adachi et al., and to the currently demonstrated faint-laser pulse system, we demonstrate that a down-conversion source in a Poissonian mode of operation can largely enhance the performance of decoy-state quantum key distribution systems. This makes the down-conversion-based decoy-state system an interesting alternative to current technological implementations based on faint-laser pulses.
The decoy-state method is widely used in practical quantum key distribution systems to replace ideal single photon sources with realistic light sources by varying intensities. Instead of active modulation, the passive decoy-state method employs built-in decoy states in a parametric down-conversion photon source, which can decrease the side channel information leakage in decoy state preparation and hence increase the security. By employing low dark count up-conversion single photon detectors, we have experimentally demonstrated the passive decoy-state method over a 50-km-long optical fiber and have obtained a key rate of about 100 bit/s. Our result suggests that the passive decoy-state source is a practical candidate for future quantum communication implementation.