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arXiv:1211.3194 · Journal of Lightwave Technology

Novel High-Speed Polarization Source for Decoy-State BB84 Quantum Key Distribution Over Free Space and Satellite Links

Zhizhong Yan, Evan Meyer-Scott, Jean-Philippe Bourgoin, Brendon L. Higgins, Nikolay Gigov, Allison MacDonald, Hannes Hübel, Thomas D. Jennewein

Published Feb 26, 2013• 34 citations
arXivHTMLPDF

Abstract

To implement the BB84 decoy-state quantum key distribution (QKD) protocol over a lossy ground-satellite quantum uplink requires a source that has high repetition rate of short laser pulses, long term stability, and no phase correlations between pulses. We present a new type of telecom optical polarization and amplitude modulator, based on a balanced Mach-Zehnder interferometer configuration, coupled to a polarization-preserving sum-frequency generation (SFG) optical setup, generating 532 nm photons with modulated polarization and amplitude states. The weak coherent pulses produced by SFG meet the challenging requirements for long range QKD, featuring a high clock rate of 76 MHz, pico-second pulse width, phase randomization, and 98% polarization visibility for all states. Successful QKD has been demonstrated using this apparatus with full system stability up to 160 minutes and channel losses as high 57 dB . We present the design and simulation of the hardware through the Mueller matrix and Stokes vector relations, together with an experimental implementation working in the telecom wavelength band. We show the utility of the complete system by performing high loss QKD simulations, and confirm that our modulator fulfills the expected performance.

DOI
10.1109/jlt.2013.2249040

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To implement the BB84 decoy-state quantum key distribution (QKD) protocol over a lossy ground-satellite quantum uplink requires a source that has high repetition rate of short laser pulses, long term stability, and no phase correlations between pulses. We present a new type of telecom optical polarization and amplitude modulator, based on a balanced Mach-Zehnder interferometer configuration, coupled to a polarization-preserving sum-frequency generation (SFG) optical setup, generating 532 nm photons with modulated polarization and amplitude states. The weak coherent pulses produced by SFG meet the challenging requirements for long range QKD, featuring a high clock rate of 76 MHz, pico-second pulse width, phase randomization, and 98% polarization visibility for all states. Successful QKD has been demonstrated using this apparatus with full system stability up to 160 minutes and channel losses as high 57 dB . We present the design and simulation of the hardware through the Mueller matrix and Stokes vector relations, together with an experimental implementation working in the telecom wavelength band. We show the utility of the complete system by performing high loss QKD simulations, and confirm that our modulator fulfills the expected performance.
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Quantum key distribution (QKD) takes advantage of fundamental properties of quantum physics to allow two distant parties to share a secret key; however, QKD is hampered by a distance limitation of a few hundred kilometers on Earth. The most immediate solution for global coverage is to use a satellite, which can receive separate QKD transmissions from two or more ground stations and act as a trusted node to link these ground stations. In this article we report on a system capable of performing QKD in the high loss regime expected in an uplink to a satellite using weak coherent pulses and decoy states. Such a scenario profits from the simplicity of its receiver payload, but has so far been considered to be infeasible due to very high transmission losses (40--50 dB). The high loss is overcome by implementing an innovative photon source and advanced timing analysis. Our system handles up to 57 dB photon loss in the infinite key limit, confirming the viability of the satellite uplink scenario. We emphasize that while this system was designed with a satellite uplink in mind, it could just as easily overcome high losses on any free space QKD link.
Free-space quantum key exchanges between ground stations and low earth orbiting satellites will be characterized by high link losses, typically of the order of 30 dB or higher. These losses, together with the need to transmit weak Poissonian laser pulses containing on average substantially less than 0.1 photons per transmitted bit to preserve security, will result in exceedingly low channel efficiencies, typically of the order of 10-5. In order to achieve even a relatively modest secure key bit rate of 100 kbps, it will therefore often be necessary to key the transmitter at rates in excess of 10 Gbps. In this paper we outline several different methods of achieving such fast polarization keying including the use of dual drive Mach-Zehnder intensity modulators on lithium niobate in a hybrid fibre-guided modulator structures. We then propose a total integrated polarization keying structure in LiNbO3. We describe the fabrication and testing of such ultra-broadband polarization keyers suitable for use in high loss, short-wave free-space quantum key distribution systems employing silicon photon counters. We also indicate how these devices may be incorporated into quantum key satellite courier payloads and ground station terminals.
We present a new optical scheme for BB84 protocol quantum key distribution (QKD). The proposed setup consists of a compact all-fiber polarization encoding optical scheme based on LiNbO3 phase modulators, single laser source and two single-photon detectors. Optical scheme consists of standard telecommunication components and is suitable for both fiber and free-space quantum communication channels. Low losses (~2dB) in Bob's device increase both the key generation rate and distance limit. A new technique for solving polarization mode dispersion (PMD) issue in LiNbO3 is implemented, allowing two crystals to neutralize the effect of each other. Several proof-of-concept experiments have been conducted at 10 MHz repetition frequency over 50 km of standard optical fiber under laboratory conditions and over 30 km of urban fiber with high losses (13dB), which is a link within a QKD network. To achieve this, calibration algorithms have been developed, allowing the system to work autonomously and making it promising for practical applications.
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