Security of the Decoy-State BB84 Protocol with Imperfect State Preparation

Abstract

The quantum key distribution (QKD) allows two remote users to share a common information-theoretic secure secret key. In order to guarantee the security of a practical QKD implementation, the physical system has to be fully characterized and all deviations from the ideal protocol due to various imperfections of realistic devices have to be taken into account in the security proof. In this work, we study the security of the efficient decoy-state BB84 QKD protocol in the presence of the source flaws, caused by imperfect intensity and polarization modulation. We investigate the non-Poissonian photon-number statistics due to coherent-state intensity fluctuations and the basis-dependence of the source due to non-ideal polarization state preparation. The analysis is supported by the experimental characterization of intensity and phase distributions.

Design and implementation of a polarization-encoding system for quantum key distribution

“…In fact, the QBER values reported include this contribution, which are therefore compatible with the implementation of a secure QKD protocol. It is worth noticing that imperfect state preparation can present a security impairment that, when taken into account, may significantly reduce the distance up to which secret key generation is possible [35]. However, such security implications can be overcome by calibrating and monitoring the detection efficiency of the SPDs [36].…”