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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Quantum Key Distribution with Heterodyne Detection

Christoffer Wittmann, Josef Urban Fürst, Carlos Wiechers, Dominique Elser, Сыч Денис Васильевич, Gerd Leuchs

Published Jun 1, 2009• 4 citations

Abstract

In this paper, we focus on the exchange of quantum states with a prototype setup and present estimated secret bit rates. The continuous-variable QKD protocol employs binary encoding in optical coherent states and postselection. In our experiment, the protocol is adapted to a long range fibre-based setup at the telecommunication wavelength (1550nm). The system employs heterodyne detection, using free-space optics and exploiting the polarisation degree of freedom. This allows for measuring the Q- functions of the transmitted signal states and the estimation of the secret key rates for different fibre lengths. Our results show an excess noise of 0.025 shot noise units, originating from the electronic detector noise and stray light of the LO in the signal arm of the detection, for different channels up to 40 km. The values for attenuation and negligible channel noise allow for an estimated secret key of about 0.001 bit per pulse and a fibre channel of 20.5 km length.

DOI: 10.1109/cleoe-eqec.2009.5194793

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We propose a novel heterodyne detection scheme for continuous-variable quantum key distribution (CVQKD), which measures both quadrature components of a quantum signal encoded in optical phase space. The proposed method uses time division to achieve identical performance to conventional heterodyne detection with only a single homodyne detection system. Our method also uses a Faraday-Michelson interferometer to make it independent of polarization drift and eliminate the need for dynamic polarization control. Our method is experimentally demonstrated using the Gaussian-modulated coherent-states (GMCS) protocol over a 20.06 km optical fiber channel, achieving an expected secret key rate of up to 0.187 Mbps.