# Postselection technique for quantum channels with applications to quantum cryptography.

@article{Christandl2008PostselectionTF, title={Postselection technique for quantum channels with applications to quantum cryptography.}, author={Matthias Christandl and Robert K{\"o}nig and Renato Renner}, journal={Physical review letters}, year={2008}, volume={102 2}, pages={ 020504 } }

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…

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