343 research outputs found
A dissipative scheme to approach the boundary of two-qubit entangled mixed states
We discuss the generation of states close to the boundary-family of maximally
entangled mixed states as defined by the use of concurrence and linear entropy.
The coupling of two qubits to a dissipation-affected bosonic mode is able to
produce a bipartite state having, for all practical purposes, the entanglement
and purity properties of one of such boundary states. We thoroughly study the
effects that thermal and squeezed character of the bosonic mode have in such a
process and we discuss tolerance to qubit phase-damping mechanisms. The
non-demanding nature of the scheme makes it realizable in a matter-light based
physical set-up, which we address in some details.Comment: 9 pages, 7 figures, RevTeX4, Accepted for publication by Physics
Review
Enhanced dynamical entanglement transfer with multiple qubits
We present two strategies to enhance the dynamical entanglement transfer from
continuous variable (CV) to finite dimensional systems by employing multiple
qubits. First, we consider the entanglement transfer to a composite finite
dimensional system of many qubits simultaneously interacting with a bipartite
CV field. We show that, considering realistic conditions in the generation of
CV entanglement, a small number of qubits resonantly coupled to the CV system
is sufficient for an almost complete dynamical transfer of the entanglement.
Our analysis also sheds further light on the transition between microscopic and
macroscopic behaviours of composite finite dimensional systems coupled to
bosonic fields (like atomic clouds interacting with light). Furthermore, we
present a protocol based on sequential interactions of the CV system with some
ancillary qubit systems and on subsequent measurements, allowing to
probabilistically convert CV entanglement into `almost perfect' Bell pairs of
two qubits. Our proposals are suited for realizations in various experimental
settings, ranging from cavity-QED to cavity-integrated superconducting devices.Comment: 10 pages, 8 figures, RevTeX4; terminology revised; accepted for
publicatio
Controllable Gaussian-qubit interface for extremal quantum state engineering
We study state engineering through bilinear interactions between two remote
qubits and two-mode Gaussian light fields. The attainable two-qubit states span
the entire physically allowed region in the entanglement-versus-global-purity
plane. Two-mode Gaussian states with maximal entanglement at fixed global and
marginal entropies produce maximally entangled two-qubit states in the
corresponding entropic diagram. We show that a small set of parameters
characterizing extremally entangled two-mode Gaussian states is sufficient to
control the engineering of extremally entangled two-qubit states, which can be
realized in realistic matter-light scenarios.Comment: 4+3 pages, 6 figures, RevTeX4. Close to published version with
appendi
Entanglement generation in harmonic chains: tagging by squeezing
We address the problem of spring-like coupling between bosons in an open
chain configuration where the counter-rotating terms are explicitly included.
We show that fruitful insight can be gained by decomposing the time-evolution
operator of this problem into a pattern of linear-optics elements. This allows
us to provide a clear picture of the effects of the counter-rotating terms in
the important problem of long-haul entanglement distribution. The analytic
control over the variance matrix of the state of the bosonic register allows us
to track the dynamics of the entanglement. This helps in designing a global
addressing scheme, complemented by a proper initialization of the register,
which quantitatively improves the entanglement between the extremal oscillators
in the chain, thus providing a strategy for feasible long distance entanglement
distribution.Comment: 8 pages, 8 figures, RevTeX
Vortex entanglement in Bose-Einstein condensates coupled to Laguerre-Gauss beams
We study the establishment of vortex entanglement in remote and weakly
interacting Bose Einstein condensates. We consider a two-mode photonic resource
entangled in its orbital angular momentum (OAM) degree of freedom and, by
exploiting the process of light-to-BEC OAM transfer, demonstrate that such
entanglement can be efficiently passed to the matter-like systems. Our proposal
thus represents a building block for novel low-dissipation and long-memory
communication channels based on OAM. We discuss issues of practical
realizability, stressing the feasibility of our scheme and present an operative
technique for the indirect inference of the set vortex entanglement.Comment: 10 pages, 7 figures, RevTex
Teleporting bipartite entanglement using maximally entangled mixed channels
The ability to teleport entanglement through maximally entangled mixed states
as defined by concurrence and linear entropy is studied. We show how the
teleported entanglement depends on the quality of the quantum channel used, as
defined through its entanglement and mixedness, as well as the form of the
target state to be teleported. We present new results based on the fidelity of
the teleported state as well as an experimental set-up that is immediately
implementable with currently available technology.Comment: 8 pages, 7 figures, RevTeX4, Accepted for publication in the IJQI
special issue on Distributed Quantum Information Processin
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