Lluis Masanes

Device-independent quantum key distribution aims to provide key distribution schemes whose security is based on the laws of quantum physics but which does not require any assumptions about the internal working of the quantum devices used in the protocol. We provide a general security proof valid for a large class of device-independent quantum key distribution protocols in a model in which the raw key elements are generated by causally independent measurement processes. The validity of this independence condition may be justifiable in a variety of implementations and is necessarily satisfied in a physical realization where the raw key is generated by N separate pairs of devices.

This talk is about secret key distribution from correlations that violate Bell inequalities. A security proof can be obtained from the assumption that arbitrarily-fast signaling between different subsystems is impossible. This assumption is imposed at the level of the outcome probabilities given the choice of observables, therefore, the scheme remains secure in situations where the honest parties distrust their quantum apparatuses.

We prove that binary linear error correcting codes (ECCs) can act as deterministic extractors in a randomness expansion protocol, achieving rates comparable to existing seeded extractors. In addition to reducing the initial randomness consumed, the computational cost of implementing some binary linear ECCs is significantly lower in terms of both computation time and memory size.

Device-independent (DI) quantum cryptography aims at providing secure cryptography with minimal trust in, or characterisation of, the underlying quantum devices. An essential step in DI protocols is randomness extraction (or privacy amplification) which requires the honest parties to have a seed of additional bits with sufficient entropy and statistical independence of any bits generated during the protocol. In this work we introduce a method for extraction in DI protocols which does not require a seed and is secure against computationally unbounded quantum adversary. The key idea is to use the Bell violation of the raw data, instead of its min-entropy, as the extractor promise.