22,636 research outputs found
Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution
Nonlocal correlations, a longstanding foundational topic in quantum
information, have recently found application as a resource for cryptographic
tasks where not all devices are trusted, for example in settings with a highly
secure central hub, such as a bank or government department, and less secure
satellite stations which are inherently more vulnerable to hardware "hacking"
attacks. The asymmetric phenomena of Einstein-Podolsky-Rosen steering plays a
key role in one-sided device-independent quantum key distribution (1sDI-QKD)
protocols. In the context of continuous-variable (CV) QKD schemes utilizing
Gaussian states and measurements, we identify all protocols that can be 1sDI
and their maximum loss tolerance. Surprisingly, this includes a protocol that
uses only coherent states. We also establish a direct link between the relevant
EPR steering inequality and the secret key rate, further strengthening the
relationship between these asymmetric notions of nonlocality and device
independence. We experimentally implement both entanglement-based and
coherent-state protocols, and measure the correlations necessary for 1sDI key
distribution up to an applied loss equivalent to 7.5 km and 3.5 km of optical
fiber transmission respectively. We also engage in detailed modelling to
understand the limits of our current experiment and the potential for further
improvements. The new protocols we uncover apply the cheap and efficient
hardware of CVQKD systems in a significantly more secure setting.Comment: Addition of experimental results and (several) new author
Factorisation properties of the strong product
We investigate a number of factorisation conditions in the frame- work of sets of probability measures, or coherent lower previsions, with finite referential spaces. We show that the so-called strong product constitutes one way to combine a number of marginal coherent lower previsions into an independent joint lower prevision, and we prove that under some conditions it is the only independent product that satisfies the factorisation conditions
Marginal extension in the theory of coherent lower previsions
AbstractWe generalise Walley’s Marginal Extension Theorem to the case of any finite number of conditional lower previsions. Unlike the procedure of natural extension, our marginal extension always provides the smallest (most conservative) coherent extensions. We show that they can also be calculated as lower envelopes of marginal extensions of conditional linear (precise) previsions. Finally, we use our version of the theorem to study the so-called forward irrelevant product and forward irrelevant natural extension of a number of marginal lower previsions
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