1,596 research outputs found
Dicke-like quantum phase transition and vacuum entanglement with two coupled atomic ensembles
We study the coherent cooperative phenomena of the system composed of two
interacting atomic ensembles in the thermodynamic limit. Remarkably, the system
exhibits the Dicke-like quantum phase transition and entanglement behavior
although the governing Hamiltonian is fundamentally different from the
spin-boson Dicke Hamiltonian, offering the opportunity for investigating
collective matter-light dynamics with pure matter waves. The model can be
realized with two Bose-Einstein condensates or atomic ensembles trapped in two
optical cavities coupled to each other. The interaction between the two
separate samples is induced by virtual photon exchange
Five-dimensional metric gravity and the accelerated universe
The metric theories of gravity are generalized to five-dimensional
spacetimes. By assuming a hypersurface-orthogonal Killing vector field
representing the compact fifth dimension, the five-dimensional theories are
reduced to their four-dimensional formalism. Then we study the cosmology of a
special class of models in a spatially flat FRW spacetime. It
is shown that the parameter can be constrained to a certain range by the
current observed deceleration parameter, and its lower bound corresponds to the
Kaluza-Klein theory. It turns out that both expansion and contraction of the
extra dimension may prescribe the smooth transition from the deceleration era
to the acceleration era in the recent past as well as an accelerated scenario
for the present universe. Hence five-dimensional gravity can naturally
account for the present accelerated expansion of the universe. Moreover, the
models predict a transition from acceleration to deceleration in the future,
followed by a cosmic recollapse within finite time. This differs from the
prediction of the five-dimensional Brans-Dicke theory but is in consistent with
a recent prediction based on loop quantum cosmology.Comment: 14 pages, 9 figures; Version published in PR
Distributed coherent manipulation of qutrits by virtual excitation processes
We propose a scheme for the deterministic coherent manipulation of two atomic
qutrits, trapped in separate cavities coupled through a short optical fibre or
optical resonator. We study such a system in the regime of dispersive
atom-field interactions, where the dynamics of atoms, cavities and fibre
operates through virtual population of both the atomic excited states and
photonic states in the cavities and fibre. We show that the resulting effective
dynamics allows for the creation of robust qutrit entanglement, and thoroughly
investigate the influence of imperfections and dissipation, due to atomic
spontaneous emission and photon leakage, on the entanglement of the two qutrits
state.Comment: 15 pages, 4 figure
Generating entanglement between microwave photons and qubits in multiple cavities coupled by a superconducting qutrit
We discuss how to generate entangled coherent states of four
\textrm{microwave} resonators \textrm{(a.k.a. cavities)} coupled by a
superconducting qubit. We also show \textrm{that} a GHZ state of four
superconducting qubits embedded in four different resonators \textrm{can be
created with this scheme}. In principle, \textrm{the proposed method} can be
extended to create an entangled coherent state of resonators and to prepare
a Greenberger-Horne-Zeilinger (GHZ) state of qubits distributed over
cavities in a quantum network. In addition, it is noted that four resonators
coupled by a coupler qubit may be used as a basic circuit block to build a
two-dimensional quantum network, which is useful for scalable quantum
information processing.Comment: 13 pages, 7 figure
Online gaming addiction: the role of sensation seeking, self-control, neuroticism, aggression, state anxiety and trait anxiety
Research into online gaming has steadily increased over the last decade, although relatively little research has examined the relationship between online gaming addiction and personality factors. This study examined the relationship between a number of personality traits (sensation seeking, self-control, aggression, neuroticism, state anxiety, and trait anxiety) and online gaming addiction. Data were collected over a 1-month period using an opportunity sample of 123 university students at an East Midlands university in the United Kingdom. Gamers completed all the online questionnaires. Results of a multiple linear regression indicated that five traits (neuroticism, sensation seeking, trait anxiety, state anxiety, and aggression) displayed significant associations with online gaming addiction. The study suggests that certain personality traits may be important in the acquisition, development, and maintenance of online gaming addiction, although further research is needed to replicate the findings of the present study
Time-Dependent Spin-Polarized Transport Through a Resonant Tunneling Structure with Multi-Terminal
The spin-dependent transport of the electrons tunneling through a resonant
tunneling structure with ferromagnetic multi-terminal under dc and ac fields is
explored by means of the nonequilibrium Green function technique. A general
formulation for the time-dependent current and the time-averaged current is
established. As its application the systems with two and three terminals in
noncollinear configurations of the magnetizations under dc and ac biases are
investigated, respectively. The asymmetric factor of the relaxation times for
the electrons with different spin in the central region is uncovered to bring
about various behaviours of the TMR. The present three-terminal device is
different from that discussed in literature, which is coined as a spin
transistor with source. The current-amplification effect is found. In addition,
the time-dependent spin transport for the two-terminal device is studied. It is
found that the photonic sidebands provide new channels for the electrons
tunneling through the barriers, and give rise to new resonances of the TMR,
which is called as the photon-asisted spin-dependent tunneling. The asymmetric
factor of the relaxation times is observed to lead to additional resonant peaks
besides the photon-asisted resonances.Comment: 32 pages,14 figure
Supersymmetric Modified Korteweg-de Vries Equation: Bilinear Approach
A proper bilinear form is proposed for the N=1 supersymmetric modified
Korteweg-de Vries equation. The bilinear B\"{a}cklund transformation of this
system is constructed. As applications, some solutions are presented for it.Comment: 8 pages, LaTeX using packages amsmath and amssymb, some corrections
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Spin-Polarized Transport in Ferromagnet-Marginal Fermi Liquid Systems
Spin-polarized transport through a marginal Fermi liquid (MFL) which is
connected to two noncollinear ferromagnets via tunnel junctions is discussed in
terms of the nonequilibrium Green function approach. It is found that the
current-voltage characteristics deviate obviously from the ohmic behavior, and
the tunnel current increases slightly with temperature, in contrast to those of
the system with a Fermi liquid. The tunnel magnetoresistance (TMR) is observed
to decay exponentially with increasing the bias voltage, and to decrease slowly
with increasing temperature. With increasing the coupling constant of the MFL,
the current is shown to increase linearly, while the TMR is found to decay
slowly. The spin-valve effect is observed.Comment: 5 pages, 6 figures, Phys. Rev. B 71, 064412 (2005
Jaynes-Cummings model with a collective atomic mode
We study the dynamics of a single control atom and an atomic sample
interacting with a nonresonant cavity mode. The control atom is driven by an
auxiliary classical field. Under certain conditions, the coherent energy
exchange between the control atom and the atomic sample induced by the cavity
mode is described by the Jaynes-Cummings model. The idea provides a possibility
for quantum-state engineering and reconstruction for collective atomic modes.Comment: arXiv admin note: text overlap with arXiv:0812.472
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