TY - JOUR

T1 - Postselection technique for quantum channels with applications to quantum cryptography

AU - Christandl, Matthias

AU - König, Robert

AU - Renner, Renato

PY - 2009/1/12

Y1 - 2009/1/12

N2 - 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 an arbitrary input, it is sufficient to consider the 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. 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 with help of the exponential de Finetti theorem.

AB - 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 an arbitrary input, it is sufficient to consider the 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. 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 with help of the exponential de Finetti theorem.

UR - http://www.scopus.com/inward/record.url?scp=59149083391&partnerID=8YFLogxK

U2 - 10.1103/PhysRevLett.102.020504

DO - 10.1103/PhysRevLett.102.020504

M3 - Article

AN - SCOPUS:59149083391

SN - 0031-9007

VL - 102

JO - Physical Review Letters

JF - Physical Review Letters

IS - 2

M1 - 020504

ER -