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CATEGORIES:CQIF Seminar
SUMMARY:Post-selection technique for quantum channels with
applications to quantum cryptography - Matthias C
hristandl (LMU Munich)
DTSTART;TZID=Europe/London:20081128T150000
DTEND;TZID=Europe/London:20081128T160000
UID:TALK15468AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/15468
DESCRIPTION:We propose a general method for studying propertie
s of quantum channels acting on an n-partite syste
m\, whose action is invariant under permutations o
f the subsystems. Our main result is that\, in ord
er 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 F
inetti-type state\, i.e.\, a state which consists
of n identical and independent copies of an (unkno
wn) state on a single subsystem. A similar stateme
nt holds for more general channels which are covar
iant with respect to the action of an arbitrary fi
nite or locally compact group. \nOur technique can
be applied to the analysis of information-theoret
ic problems. For example\, in quantum cryptography
\, we get a simple proof for the fact that securit
y of a discrete-variable quantum key distribution
protocol against collective attacks implies securi
ty of the protocol against the most general attack
s. The resulting security bounds are tighter than
previously known bounds obtained by proofs relying
on the exponential de Finetti theorem [Renner\, N
ature Physics 3\,645(2007)]. \n \nReference: http:
//arxiv.org/abs/0809.3019
LOCATION:MR14\, Centre for Mathematical Sciences
CONTACT:Lawrence Ioannou
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