Simple performance evaluation of pulsed spontaneous parametric down-conversion sources for quantum communications

Fast and complete characterization of pulsed spontaneous parametric down conversion (SPDC) sources is important for applications in quantum information processing and communications. We propose a simple method to perform this task, which only requires measuring the counts on the two output channels and the coincidences between them, as well as modeling the filter used to reduce the source bandwidth. The proposed method is experimentally tested and used for a complete evaluation of SPDC sources (pair emission probability, total losses, and fidelity) of different bandwidths. This method can find applications in the setting up of SPDC sources and in the continuous verification of the quality of quantum communication links

Experimental vulnerability analysis of QKD based on attack ratings

Abstract Inspired by the methodology used for classical cryptographic hardware, we consider the use of attack ratings in the context of QKD security evaluation. To illustrate the relevance of this approach, we conduct an experimental vulnerability assessment of CV-QKD against saturation attacks, for two different attack strategies. The first strategy relies on inducing detector saturation by performing a large coherent displacement. This strategy is experimentally challenging and therefore translates into a high attack rating. We also propose and experimentally demonstrate a second attack strategy that simply consists in saturating the detector with an external laser. The low rating we obtain indicates that this attack constitutes a primary threat for practical CV-QKD systems. These results highlight the benefits of combining theoretical security considerations with vulnerability analysis based on attack ratings, in order to guide the design and engineering of practical QKD systems towards the highest possible security standards

Réalisation expérimentale de sources de photons uniques, caractérisation et application à la cryptographie quantique

A single photon source is an emitter that is able to produce light plses containing exactly one photon. We present the work related to the experimental realisation and the statistical characterisation of single photon sources of two kinds : * Triggerred single photon sources, based on the temporal control of a single fluorescent emitter. We used single molecules and single NV coloured centres of diamond as single emitters. * Sources of heralded single photons, based on the conditionnal preparation of one-photon states, obtained from photon pairs produced by parametric down-conversion in a non-linear crystal. Two of the single photon sources we have realised have been used in experimental quantum key distribution test-beds. The measured experimental performances indicate that a potential gain can be obtained bu using a single photon source instead of weak coherent pulses.Une source de photons uniques est un émetteur lumineux capable de produire des impulsions contenant exactement un photon. Nous présentons le travail lié à la réalisation expérimentale et à la caractérisation statistique de deux types de sources de photons uniques: * Les sources déclenchées de photons uniques, reposant sur la contrôle de la fluorescence d'un émetteur individuel. Nous avons utilisé des molécules uniques ainsi que des centres colorés NV uniques du diamant comme émetteurs individuels. * Les sources de photons annoncés, reposant sur la préparation conditionnelle d'états à un photon à partir de paires de photons produites par fluorescence paramétrique dans un cristal non-linéaire. Deux des sources de photons uniques réalisées ont été utilisées dans des expériences de distribution quantique de clé, dont les résultats illustrent les avantages que procure l'utilisation d'une source de photons uniques vis-à-vis de systèmes reposant sur des impulsions cohérentes atténuées

Architecture of the Secoqc quantum key distribution network

The European projet Secoqc (Secure Communication based on Quantum Cryptography) aims at developing a global network for unconditionally secure key distribution. This paper specifies the requirements and presents the principles guiding the design of this network, and relevant to its architecture and protocols