Karel Lemr, Karol Bartkiewicz, Antonin Cernoch, Jan Soubusta, Adam Miranowicz
We present the first experimental implementation of a multifunctional optimal
quantum cloner. Previous implementations have always been designed to optimize
the cloning procedure with respect to one single type of it a priori
information about the cloned state. In contrast, our "all in one"
implementation is optimal for several prominent regimes such as universal
cloning, phase-covariant cloning and also, the first ever realized mirror
phase-covariant cloning, when the square of the expected value of Pauli's Z
operator is known in advance. In all these regimes the experimental device
yields clones with almost maximum achievable average fidelity (97.5% of
theoretical limit). Our device has a wide range of possible applications in
quantum information processing especially in quantum communication. For
instance, one can use it for incoherent and coherent attacks against a variety
of cryptographic protocols including the BB84 protocol of quantum key
distribution through the Pauli damping channels. It can be also applied as a
state-dependent photon multiplier in practical quantum networks.
View original:
http://arxiv.org/abs/1201.6234
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