We report "plug & play" and free-space implementations of continuous-variable (CV) quantum key distribution (QKD). In a CV QKD system, a homodyne detector is used to detect a weak signal light by superposing the signal with a local oscillator (LO) whose intensity is much stronger than the signal. In conventional "plug & play" (or auto compensating) systems, two pulses traverse an identical optical path and the intensities of them become equal. In our experiment we use an acousto-optic modulator and have successfully controlled the intensities of the signal and the LO. For free-space implementation of CV QKD the stability of the double interferometer is a crucial problem. We have separated the signal and LO in time longer than the coherence time of the pulse by exploiting the birefringence of EOM crystals. In this setup the signal and LO traverse along the same ray path, so the stability of the interferometer is greatly improved.

Date Published: 12 May 2006
PDF: 7 pages
Proc. SPIE 6244, Quantum Information and Computation IV, 62440O (12 May 2006); doi: 10.1117/12.665460

Published in SPIE Proceedings Vol. 6244:
Quantum Information and Computation IV
Eric J. Donkor; Andrew R. Pirich; Howard E. Brandt, Editor(s)