4,956 research outputs found
Entangled and disentangled evolution for a single atom in a driven cavity
For an atom in an externally driven cavity, we show that special initial
states lead to near-disentangled atom-field evolution, and superpositions of
these can lead to near maximally-entangled states. Somewhat counterintutively,
we find that (moderate) spontaneous emission in this system actually leads to a
transient increase in entanglement beyond the steady-state value. We also show
that a particular field correlation function could be used, in an experimental
setting, to track the time evolution of this entanglement
From quantum feedback to probabilistic error correction: Manipulation of quantum beats in cavity QED
It is shown how to implement quantum feedback and probabilistic error
correction in an open quantum system consisting of a single atom, with ground-
and excited-state Zeeman structure, in a driven two-mode optical cavity. The
ground state superposition is manipulated and controlled through conditional
measurements and external fields, which shield the coherence and correct
quantum errors. Modeling of an experimentally realistic situation demonstrates
the robustness of the proposal for realization in the laboratory
A Molecular Matter-Wave Amplifier
We describe a matter-wave amplifier for vibrational ground state molecules,
which uses a Feshbach resonance to first form quasi-bound molecules starting
from an atomic Bose-Einstein condensate. The quasi-bound molecules are then
driven into their stable vibrational ground state via a two-photon Raman
transition inside an optical cavity. The transition from the quasi-bound state
to the electronically excited state is driven by a classical field.
Amplification of ground state molecules is then achieved by using a strongly
damped cavity mode for the transition from the electronically excited molecules
to the molecular ground state
Model of the optical emission of a driven semiconductor quantum dot: phonon-enhanced coherent scattering and off-resonant sideband narrowing
We study the crucial role played by the solid-state environment in
determining the photon emission characteristics of a driven quantum dot. For
resonant driving, we predict a phonon-enhancement of the coherently emitted
radiation field with increasing driving strength, in stark contrast to the
conventional expectation of a rapidly decreasing fraction of coherent emission
with stronger driving. This surprising behaviour results from thermalisation of
the dot with respect to the phonon bath, and leads to a nonstandard regime of
resonance fluorescence in which significant coherent scattering and the Mollow
triplet coexist. Off-resonance, we show that despite the phonon influence,
narrowing of dot spectral sideband widths can occur in certain regimes,
consistent with an experimental trend.Comment: Published version. 5 pages, 2 figures, plus 4 page supplement. Title
changed, figure 1 revised, various edits and additions to the tex
Cooling trapped atoms in optical resonators
We derive an equation for the cooling dynamics of the quantum motion of an
atom trapped by an external potential inside an optical resonator. This
equation has broad validity and allows us to identify novel regimes where the
motion can be efficiently cooled to the potential ground state. Our result
shows that the motion is critically affected by quantum correlations induced by
the mechanical coupling with the resonator, which may lead to selective
suppression of certain transitions for the appropriate parameters regimes,
thereby increasing the cooling efficiency.Comment: 4 pages, 3 figures; version published in PR
Time evolution and squeezing of the field amplitude in cavity QED
We present the conditional time evolution of the electromagnetic field
produced by a cavity QED system in the strongly coupled regime. We obtain the
conditional evolution through a wave-particle correlation function that
measures the time evolution of the field after the detection of a photon. A
connection exists between this correlation function and the spectrum of
squeezing which permits the study of squeezed states in the time domain. We
calculate the spectrum of squeezing from the master equation for the reduced
density matrix using both the quantum regression theorem and quantum
trajectories. Our calculations not only show that spontaneous emission degrades
the squeezing signal, but they also point to the dynamical processes that cause
this degradation.Comment: 12 pages. Submitted to JOSA
Aerodynamic analysis of three advanced configurations using the TranAir full-potential code
Computational results are presented for three advanced configurations: the F-16A with wing tip missiles and under wing fuel tanks, the Oblique Wing Research Aircraft, and an Advanced Turboprop research model. These results were generated by the latest version of the TranAir full potential code, which solves for transonic flow over complex configurations. TranAir embeds a surface paneled geometry definition in a uniform rectangular flow field grid, thus avoiding the use of surface conforming grids, and decoupling the grid generation process from the definition of the configuration. The new version of the code locally refines the uniform grid near the surface of the geometry, based on local panel size and/or user input. This method distributes the flow field grid points much more efficiently than the previous version of the code, which solved for a grid that was uniform everywhere in the flow field. TranAir results are presented for the three configurations and are compared with wind tunnel data
Dissipation-driven quantum phase transitions in collective spin systems
We consider two different collective spin systems subjected to strong
dissipation -- on the same scale as interaction strengths and external fields
-- and show that either continuous or discontinuous dissipative quantum phase
transitions can occur as the dissipation strength is varied. First, we consider
a well known model of cooperative resonance fluorescence that can exhibit a
second-order quantum phase transition, and analyze the entanglement properties
near the critical point. Next, we examine a dissipative version of the
Lipkin-Meshkov-Glick interacting collective spin model, where we find that
either first- or second-order quantum phase transitions can occur, depending
only on the ratio of the interaction and external field parameters. We give
detailed results and interpretation for the steady state entanglement in the
vicinity of the critical point, where it reaches a maximum. For the first-order
transition we find that the semiclassical steady states exhibit a region of
bistability.Comment: 12 pages, 16 figures, removed section on homodyne spectr
Strong-coupling of quantum dots in microcavities
We show that strong-coupling (SC) of light and matter as it is realized with
quantum dots (QDs) in microcavities differs substantially from the paradigm of
atoms in optical cavities. The type of pumping used in semiconductors yields
new criteria to achieve SC, with situations where the pump hinders, or on the
contrary, favours it. We analyze one of the seminal experimental observation of
SC of a QD in a pillar microcavity [Reithmaier et al., Nature (2004)] as an
illustration of our main statements.Comment: Substantially revised version. The major change is in the analysis of
one of the seminal experiment of the field, that shows the excellent
quantitative agreement with the theory. Full details, especially all
concerning Fermi statistics (still present in previous versions), are now to
be presented elsewhere. To be published in Phys. Rev. Lett. 101 (2008
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