text: Two of the most intriguing features of quantum physics are the uncertainty principle and the occurrence of nonlocal correlations. The uncertainty principle states that there exist pairs of incompatible measurements on quantum systems such that their outcomes cannot both be predicted. On the other hand, nonlocal correlations of measurement outcomes at different locations cannot be explained by classical physics, but appear in the presence of entanglement. Here, we show that these two fundamental quantum effects are quantitatively related. Namely, we provide an entropic uncertainty relation for the outcomes of two binary measurements, where the lower bound on the uncertainty is quantified in terms of the maximum Clauser–Horne–Shimony–Holt value that can be achieved with these measurements. We discuss applications of this uncertainty relation in quantum cryptography, in particular, to certify quantum sources using untrusted devices.
  @cite_22: 
  @cite_36: We prove that a quantum circuit together with measurement apparatuses and EPR sources can be self-tested, i.e. fully verified without any reference to some trusted set of quantum devices. To achieve our goal we define the notions of simulation and equivalence. Using these two concepts, we construct sets of simulation conditions which imply that the physical device of interest is equivalent to the one it is supposed to implement. Another benefit of our formalism is that our statements can be proved to be robust. Finally, we design a test for quantum circuits whose complexity is polynomial in the number of gates and qubits, and the required precision.
  @cite_52: We present the optimal collective attack on a quantum key distribution protocol in the "device-independent" security scenario, where no assumptions are made about the way the quantum key distribution devices work or on what quantum system they operate. Our main result is a tight bound on the Holevo information between one of the authorized parties and the eavesdropper, as a function of the amount of violation of a Bell-type inequality.
  @cite_56: We consider quantum key distribution in the device-independent scenario, i.e., where the legitimate parties do not know (or trust) the exact specification of their apparatus. We show how secure key distribution can be realized against the most general attacks by a quantum adversary under the condition that measurements on different subsystems by the honest parties commute.
  @cite_23: Device-independent quantum key distribution aims to distribute cryptographic keys without requiring assumptions about the quantum devices in the protocol. Here, a general security proof is reported for a class of quantum key distribution protocols, which could aid the development of highly secure encryption.
  @cite_58: Randomness is an important resource for many applications, from gambling to secure communication. However, guaranteeing that the output from a candidate random source could not have been predicted by an outside party is a challenging task, and many supposedly random sources used today provide no such guarantee. Quantum solutions to this problem exist, for example a device which internally sends a photon through a beamsplitter and observes on which side it emerges, but, presently, such solutions require the user to trust the internal workings of the device. Here, we seek to go beyond this limitation by asking whether randomness can be generated using untrusted devices—even ones created by an adversarial agent—while providing a guarantee that no outside party (including the agent) can predict it. Since this is easily seen to be impossible unless the user has an initially private random string, the task we investigate here is private randomness expansion. We introduce a protocol for private randomness expansion with untrusted devices which is designed to take as input an initially private random string and produce as output a longer private random string. We point out that private randomness expansion protocols are generally vulnerable to attacks that can render the initial string partially insecure, even though that string is used only inside a secure laboratory; our protocol is designed to remove this previously unconsidered vulnerability by privacy amplification. We also discuss extensions of our protocol designed to generate an arbitrarily long random string from a finite initially private random string. The security of these protocols against the most general attacks is left as an open question.
summary: Device-independent quantum key distribution @cite_36 @cite_52 @cite_22 @cite_56 @cite_23 and randomness generation @cite_58 usually bases security on a relation between nonlocality and the randomness of the outcomes relative to some (quantum) adversary. Our result allows to split the security analysis of these protocols into two parts: the nonlocality of the measured correlations first gives a bound on the uncertainty of local measurement outcomes, which in turn can be used to ensure security. The two parts can be analyzed independently and thus our methods can be used to simplify such an analysis and, potentially, reduce the required assumptions.