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University of Cambridge > Talks.cam > CQIF Seminar > Post-selection technique for quantum channels with applications to quantum cryptography

## Post-selection technique for quantum channels with applications to quantum cryptographyAdd to your list(s) Download to your calendar using vCal - Matthias Christandl (LMU Munich)
- Friday 28 November 2008, 15:00-16:00
- MR14, Centre for Mathematical Sciences.
If you have a question about this talk, please contact Lawrence Ioannou. We propose a general method for studying properties of quantum channels acting on an n-partite system, whose action is invariant under permutations of the subsystems. Our main result is that, in order to prove that a certain property holds for any arbitrary input, it is sufficient to consider the special case where the input is a particular de Finetti-type state, i.e., a state which consists of n identical and independent copies of an (unknown) state on a single subsystem. A similar statement holds for more general channels which are covariant with respect to the action of an arbitrary finite or locally compact group. Our technique can be applied to the analysis of information-theoretic problems. For example, in quantum cryptography, we get a simple proof for the fact that security of a discrete-variable quantum key distribution protocol against collective attacks implies security of the protocol against the most general attacks. The resulting security bounds are tighter than previously known bounds obtained by proofs relying on the exponential de Finetti theorem [Renner, Nature Physics 3,645(2007)]. Reference: http://arxiv.org/abs/0809.3019 This talk is part of the CQIF Seminar series. ## This talk is included in these lists:- All CMS events
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