Sommaire:

Quantum cryptography is the most mature quantum information technology and there exist several companies selling quantum cryptography products. In recent years, several attacks have hacked quantum cryptography implementations. These attacks have proven that implementations of quantum cryptography are subtler than expected and that any mismatch between theory and experiment may open important security loopholes. To close this gap, we introduce the device-independent approach to quantum information theory in which devices are just seen as quantum black boxes processing classical information. This level of abstraction makes the protocols defined in this scenario insensitive to the recent hacking attacks.

We then discuss the device-independent scenario from a more fundamental point of view and introduce the set of almost quantum correlations. We prove that this set (i) is supra-quantum, as it predicts correlations that are impossible in the quantum formalism but (ii) is operationally equivalent to the quantum set for many information tasks. These results then demonstrate that it is possible to modify the structure of quantum correlations without running into any strong operational contradiction with quantum predictions. Intriguingly, the set of almost quantum correlations can also be derived within the history approach introduced in the context of quantum gravity.

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