3,226 research outputs found
Entanglement versus mixedness for coupled qubits under a phase damping channel
Quantification of entanglement against mixing is given for a system of
coupled qubits under a phase damping channel. A family of pure initial joint
states is defined, ranging from pure separable states to maximally entangled
state. An ordering of entanglement measures is given for well defined initial
state amount of entanglement.Comment: 9 pages, 2 figures. Replaced with final published versio
Semiclassical limit of the entanglement in closed pure systems
We discuss the semiclassical limit of the entanglement for the class of
closed pure systems. By means of analytical and numerical calculations we
obtain two main results: (i) the short-time entanglement does not depend on
Planck's constant and (ii) the long-time entanglement increases as more
semiclassical regimes are attained. On one hand, this result is in contrast
with the idea that the entanglement should be destroyed when the macroscopic
limit is reached. On the other hand, it emphasizes the role played by
decoherence in the process of emergence of the classical world. We also found
that, for Gaussian initial states, the entanglement dynamics may be described
by an entirely classical entropy in the semiclassical limit.Comment: 8 pages, 2 figures (accepted for publication in Phys. Rev. A
Non-Gaussian two-mode squeezing and continuous variable entanglement of linearly and circularly polarized light beams interacting with cold atoms
We investigate how entangled coherent states and superpositions of low
intensity coherent states of non-Gaussian nature can be generated via
non-resonant interaction between either two linearly or circularly polarized
field modes and an ensemble of X-like four-level atoms placed in an optical
cavity. We compare our results to recent experimental observations and argue
that the non-Gaussian structure of the field states may be present in those
systems.Comment: 10 pages, 7 figures, replaced with final published versio
Kerr nonlinearities and nonclassical states with superconducting qubits and nanomechanical resonators
We propose the use of a superconducting charge qubit capacitively coupled to
two resonant nanomechanical resonators to generate Yurke-Stoler states, i.e.
quantum superpositions of pairs of distinguishable coherent states 180
out of phase with each other. This is achieved by effectively implementing Kerr
nonlinearities induced through application of a strong external driving field
in one of the resonators. A simple study of the effect of dissipation on our
scheme is also presented, and lower bounds of fidelity and purity of the
generated state are calculated. Our procedure to implement a Kerr nonlinearity
in this system may be used for high precision measurements in nanomechanical
resonators.Comment: 5 pages, 2 figures, fixed typo
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