3 research outputs found
Full security of quantum key distribution from no-signaling constraints
We analyze a cryptographic protocol for generating a distributed secret key
from correlations that violate a Bell inequality by a sufficient amount, and
prove its security against eavesdroppers, constrained only by the assumption
that any information accessible to them must be compatible with the
non-signaling principle. The claim holds with respect to the state-of-the-art
security definition used in cryptography, known as universally-composable
security. The non-signaling assumption only refers to the statistics of
measurement outcomes depending on the choices of measurements; hence security
is independent of the internal workings of the devices --- they do not even
need to follow the laws of quantum theory. This is relevant for practice as a
correct and complete modeling of realistic devices is generally impossible. The
techniques developed are general and can be applied to other Bell
inequality-based protocols. In particular, we provide a scheme for estimating
Bell-inequality violations when the samples are not independent and identically
distributed.Comment: 15 pages, 2 figur
Device-independent quantum key distribution secure against collective attacks
Device-independent quantum key distribution (DIQKD) represents a relaxation
of the security assumptions made in usual quantum key distribution (QKD). As in
usual QKD, the security of DIQKD follows from the laws of quantum physics, but
contrary to usual QKD, it does not rely on any assumptions about the internal
working of the quantum devices used in the protocol. We present here in detail
the security proof for a DIQKD protocol introduced in [Phys. Rev. Lett. 98,
230501 (2008)]. This proof exploits the full structure of quantum theory (as
opposed to other proofs that exploit the no-signalling principle only), but
only holds again collective attacks, where the eavesdropper is assumed to act
on the quantum systems of the honest parties independently and identically at
each round of the protocol (although she can act coherently on her systems at
any time). The security of any DIQKD protocol necessarily relies on the
violation of a Bell inequality. We discuss the issue of loopholes in Bell
experiments in this context.Comment: 25 pages, 3 figure
Measuring Measurement: Theory and Practice
Recent efforts have applied quantum tomography techniques to the calibration
and characterization of complex quantum detectors using minimal assumptions. In
this work we provide detail and insight concerning the formalism, the
experimental and theoretical challenges and the scope of these tomographical
tools. Our focus is on the detection of photons with avalanche photodiodes and
photon number resolving detectors and our approach is to fully characterize the
quantum operators describing these detectors with a minimal set of well
specified assumptions. The formalism is completely general and can be applied
to a wide range of detectorsComment: 22 pages, 27 figure