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Q: Fachverband Quantenoptik und Photonik

Q 48: Quanteninformation: Quantenkommunikation I

Q 48.2: Talk

Thursday, March 5, 2009, 14:15–14:30, Audi-B

Fiber-based QKD system with Heterodyne Detection of Coherent States — •Christoffer Wittmann¹, Josef Fürst¹, Carlos Wiechers^1,2, Dominique Elser¹, Denis Sych¹, and Gerd Leuchs¹ — ¹Max-Planck-Institut für die Physik des Lichts , Günther-Scharowsky-Str. 1 / Bau 24, 91058 Erlangen, Germany — ²Instituto de Física de la Universidad de Guanajuato

We present a fibre-based continuous-variable quantum key distribution system. It uses weak optical coherent states at the telecommunication wavelength (1550nm) as a quantum signal. The signal and a local oscillator are sent through an optical fiber using a time and polarization multiplexing technique. The system is automated such that the polarisation drift in the channel is compensated. In the receiver, a heterodyne detector measures conjugate quadratures of the signal [1] without any prior knowledge about the signal phase. We reconstruct the Q-function of the transmitted signal for the channel lengths 3m, 20km and 40km. The estimated excess noise originating from the channel transmission is about 1% percent. The channel attenuation allows for an estimated secret key of about 0.001 bit per pulse for a fibre channel of 20km length.

[1] S. Lorenz, N. Korolkova, and G. Leuchs, Appl. Phys. B: Lasers Opt. 79, 273 (2004).