Enhancing security of practical quantum key distribution: two-layer QKD and backflash emission from silicon avalanche photodiodes

Abstract

The development of new quantum communication technologies for optical networks will enable inviolable protocols to exchange secure information. The first and more ro-bust among them is the quantum key distribution (QKD). Although in theory the security is proven unconditionally safe, the implementation in optical networks can still produce flaws due the non-ideal behavior of the optical and optoelectronic devices. In this direc-tion, this thesis presents two contributions to improve security of QKD systems. The first is the redesign of two QKD protocols to use two quantum states of light, the coherent and thermal state, with a polarization randomness. The protocols are the differential quadrature phase shift QKD and QKD using homodyne detection. The second contribution is the experimental characterization of the light emitted by avalanche photodiodes during a detection and its implication in the security of the BB84 QKD protocol.