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RIVF International Conference on Computing and Communication Technologies (RIVF)

Quantum key distribution system using dual-threshold homodyne detection

Qing Xu, Manuel Sabban, Philippe B. Gallion, Francisco Javier Mendieta

Published Jul 1, 2008• 5 citations
Publisher

Abstract

In this work we present the principles of a flexible quantum key distribution (QKD) system using quadrature-phase-shift-keying (QPSK) base and symbol encoding and dual-threshold balanced homodyne detection (BHD) scheme. We give its security proofs and we compare its performance experimentally with a photon counting detection scheme.
DOI
10.1109/rivf.2008.4586325

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Optical homodyne detection has been widely used in continuous-variable (CV) quantum information processing for measuring field quadrature. In this paper we explore the possibility of operating a conjugate homodyne detection system in ``photon counting'' mode to implement discrete-variable (DV) quantum key distribution (QKD). A conjugate homodyne detection system, which consists of a beam splitter followed by two optical homodyne detectors, can simultaneously measure a pair of conjugate quadratures XXX and PPP of the incoming quantum state. In classical electrodynamics, X2+P2{X}^{2}+{P}^{2}X2+P2 is proportional to the energy (the photon number) of the input light. In quantum optics, XXX and PPP do not commute and thus the above photon-number measurement is intrinsically noisy. This implies that a blind application of standard security proofs of QKD could result in pessimistic performance. We overcome this obstacle by taking advantage of two special features of the proposed detection scheme. First, the fundamental detection noise associated with vacuum fluctuations cannot be manipulated by an external adversary. Second, the ability to reconstruct the photon number distribution at the receiver's end can place additional constraints on possible attacks from the adversary. As an example, we study the security of the BB84 QKD using conjugate homodyne detection and evaluate its performance through numerical simulations. This study may open the door to a family of QKD protocols, complementary to the well-established DV-QKD based on single-photon detection and CV-QKD based on coherent detection.
This paper presents the principles and experimental results of an optical fiber QKD system operating at 1550 nm, and using the BB84 protocol with QPSK signals. Our experimental setup consists of a time-multiplexed super-homodyne configuration using P.I.N detectors in a differential scheme as an alternative to avalanche photon counting. Transmission over 11km of optical fiber has been done using this detection scheme and major relevant characteristics such as noise, quantum efficiency and bit error rate (BER) are reported.