634 research outputs found
Generation of Quantum Correlations in Bipartite Gaussian Open Quantum Systems
We describe the generation of quantum correlations (entanglement, discord and steering) in a system composed of two coupled non-resonant bosonic modes immersed in a common thermal reservoir, in the framework of the theory of open systems. We show that for separable initial squeezed thermal states entanglement generation may take place, for definite values of squeezing parameter, average photon numbers, temperature of the thermal bath, dissipation constant and strength of interaction between the two bosonic modes. We also show that for initial uni-modal squeezed states Gaussian discord can be generated for all non-zero values of the strength of interaction between the modes. Likewise, for an initial separable state, a generation of Gaussian steering may take place temporarily, for definite values of the parameters characterizing the initial state and the thermal environment, and the strength of coupling between the two modes
Entanglement dynamics of bipartite system in squeezed vacuum reservoirs
Entanglement plays a crucial role in quantum information protocols, thus the
dynamical behavior of entangled states is of a great importance. In this paper
we suggest a useful scheme that permits a direct measure of entanglement in a
two-qubit cavity system. It is realized in the cavity-QED technology utilizing
atoms as fying qubits. To quantify entanglement we use the concurrence. We
derive the conditions, which assure that the state remains entangled in spite
of the interaction with the reservoir. The phenomenon of sudden death
entanglement (ESD) in a bipartite system subjected to squeezed vacuum reservoir
is examined. We show that the sudden death time of the entangled states depends
on the initial preparation of the entangled state and the parameters of the
squeezed vacuum reservoir.Comment: 10 pages, 5 figures, CEWQO17(St Andrews
Dynamics of quantum entanglement in Gaussian open systems
In the framework of the theory of open systems based on completely positive
quantum dynamical semigroups, we give a description of the dynamics of
entanglement for a system consisting of two uncoupled harmonic oscillators
interacting with a thermal environment. Using Peres-Simon necessary and
sufficient criterion for separability of two-mode Gaussian states, we describe
the evolution of entanglement in terms of the covariance matrix for a Gaussian
input state. For some values of the temperature of environment, the state keeps
for all times its initial type: separable or entangled. In other cases,
entanglement generation, entanglement sudden death or a repeated collapse and
revival of entanglement take place. We determine the asymptotic Gaussian
maximally entangled mixed states (GMEMS) and their corresponding asymptotic
maximal logarithmic negativity.Comment: 10 pages, 2 figures; talk at the International Workshop on Quantum
Non-Stationary Systems, Brasilia, Brazil (2009
Formal concept analysis and structures underlying quantum logics
A Hilbert space induces a formal context, the Hilbert formal context , whose associated concept lattice is isomorphic to the lattice of closed subspaces of . This set of closed subspaces, denoted , is important in the development of quantum logic and, as an algebraic structure, corresponds to a so-called ``propositional system'', that is, a complete, atomistic, orthomodular lattice which satisfies the covering law.
In this paper, we continue with our study of the Chu construction by introducing the Chu correspondences between Hilbert contexts, and showing that the category of Propositional Systems, PropSys, is equivalent to the category of of Chu correspondences between Hilbert contextsUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
New method for the time calibration of an interferometric radio antenna array
Digital radio antenna arrays, like LOPES (LOFAR PrototypE Station), detect
high-energy cosmic rays via the radio emission from atmospheric extensive air
showers. LOPES is an array of dipole antennas placed within and triggered by
the KASCADE-Grande experiment on site of the Karlsruhe Institute of Technology,
Germany. The antennas are digitally combined to build a radio interferometer by
forming a beam into the air shower arrival direction which allows measurements
even at low signal-to-noise ratios in individual antennas. This technique
requires a precise time calibration. A combination of several calibration steps
is used to achieve the necessary timing accuracy of about 1 ns. The group
delays of the setup are measured, the frequency dependence of these delays
(dispersion) is corrected in the subsequent data analysis, and variations of
the delays with time are monitored. We use a transmitting reference antenna, a
beacon, which continuously emits sine waves at known frequencies. Variations of
the relative delays between the antennas can be detected and corrected for at
each recorded event by measuring the phases at the beacon frequencies.Comment: 9 pages, 9 figures, 1 table, pre-print of article published in
Nuclear Inst. and Methods in Physics Research, A, available at:
http://www.sciencedirect.com/science/article/B6TJM-4Y9CF4B-4/2/37bfcb899a0f387d9875a5a0729593a
Solution of the Lindblad Equation in the Kraus Representation
The so-called Lindblad equation, a typical master equation describing the
dissipative quantum dynamics, is shown to be solvable for finite-level systems
in a compact form without resort to writing it down as a set of equations among
matrix elements. The solution is then naturally given in an operator form,
known as the Kraus representation. Following a few simple examples, the general
applicability of the method is clarified.Comment: 9 page
Robustness of spatial Penning trap modes against environment-assisted entanglement
The separability of the spatial modes of a charged particle in a Penning trap
in the presence of an environment is studied by means of the positive partial
transpose (PPT) criterion. Assuming a weak Markovian environment, described by
linear Lindblad operators, our results strongly suggest that the environmental
coupling of the axial and cyclotron degrees of freedom does not lead to
entanglement at experimentally realistic temperatures. We therefore argue that,
apart from unavoidable decoherence, the presence of such an environment does
not alter the effectiveness of recently suggested quantum information protocols
in Penning traps, which are based on the combination of a spatial mode with the
spin of the particle.Comment: 11 pages, 2 figure
Intrinsic Decoherence Dynamics in Smooth Hamiltonian Systems: Quantum-classical Correspondence
A direct classical analog of the quantum dynamics of intrinsic decoherence in
Hamiltonian systems, characterized by the time dependence of the linear entropy
of the reduced density operator, is introduced. The similarities and
differences between the classical and quantum decoherence dynamics of an
initial quantum state are exposed using both analytical and computational
results. In particular, the classicality of early-time intrinsic decoherence
dynamics is explored analytically using a second-order perturbative treatment,
and an interesting connection between decoherence rates and the stability
nature of classical trajectories is revealed in a simple approximate classical
theory of intrinsic decoherence dynamics. The results offer new insights into
decoherence, dynamics of quantum entanglement, and quantum chaos.Comment: 12 pages, 7 figures, to appear in Physical Review
Chaos and Quantum-Classical Correspondence via Phase Space Distribution Functions
Quantum-classical correspondence in conservative chaotic Hamiltonian systems
is examined using a uniform structure measure for quantal and classical phase
space distribution functions. The similarities and differences between quantum
and classical time-evolving distribution functions are exposed by both
analytical and numerical means. The quantum-classical correspondence of
low-order statistical moments is also studied. The results shed considerable
light on quantum-classical correspondence.Comment: 16 pages, 5 figures, to appear in Physical Review
Test Particle in a Quantum Gas
A master equation with a Lindblad structure is derived, which describes the
interaction of a test particle with a macroscopic system and is expressed in
terms of the operator valued dynamic structure factor of the system. In the
case of a free Fermi or Bose gas the result is evaluated in the Brownian limit,
thus obtaining a single generator master equation for the description of
quantum Brownian motion in which the correction due to quantum statistics is
explicitly calculated. The friction coefficients for Boltzmann and Bose or
Fermi statistics are compared.Comment: 9 pages, revtex, no figure
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