Genuine multipartite entanglement of a quantum system can be partially
destroyed by local decoherence. Is it possible to retrieve the entanglement to
some extent by a single local operation? The answer to this question depends
very much on the type of initial genuine entanglement. For initially pure W and
cluster states and if the decoherence is given by generalized amplitude
damping, the answer is shown to be positive. In this case, the entanglement
retrieving is achieved just by redistributing the remained entanglement of the
system.Comment: 4 pages, 5 figure
We study entanglement dynamics of the three-qubit system which is initially prepared in pure Greenberger-Horne-Zeilinger (GHZ) or W state and transmitted through one of the Pauli channels σz, σx, σy or the depolarizing channel. With the help of the lower bound for three-qubit concurrence we show that the W state preserves more entanglement than the GHZ state in transmission through the Pauli channel σz. For the Pauli channels σx, σy and the depolarizing channel, however, the entanglement of the GHZ state is more resistant against decoherence than the W-type entanglement. We also briefly discuss how the accuracy of the lower bound approximation depends on the rank of the density matrix under consideration.
The idea of information encoding on quantum bearers and its quantum-mechanical processing has revolutionized our world and brought mankind on the verge of enigmatic era of quantum technologies. Inspired by this idea, in present paper we search for advantages of quantum information processing in the field of machine learning. Exploiting only basic properties of the Hilbert space, superposition principle of quantum mechanics and quantum measurements, we construct a quantum analog for Rosenblatt's perceptron, which is the simplest learning machine. We demonstrate that the quantum perceptron is superior its classical counterpart in learning capabilities. In particular, we show that the quantum perceptron is able to learn an arbitrary (Boolean) logical function, perform the classification on previously unseen classes and even recognize the superpositions of learned classes -the task of high importance in applied medical engineering.
We propose a scheme for creating of a maximally entangled state comprising
two field quanta. In our scheme, two weak light fields, which are initially
prepared in either coherent or polarization states, interact with a composite
medium near an interface between a dielectric and a negative index
metamaterial. Such interaction leads to a large Kerr nonlinearity, reduction of
the group velocity of the light and significant confinement of the light fields
while simultaneously avoiding amplitude losses of the incoming radiation. All
these considerations make our scheme efficient.Comment: 3 figures, 34 reference
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