16,526 research outputs found
Frequency up- and down-conversions in two-mode cavity quantum electrodynamics
In this letter we present a scheme for the implementation of frequency up-
and down-conversion operations in two-mode cavity quantum electrodynamics
(QED). This protocol for engineering bilinear two-mode interactions could
enlarge perspectives for quantum information manipulation and also be employed
for fundamental tests of quantum theory in cavity QED. As an application we
show how to generate a two-mode squeezed state in cavity QED (the original
entangled state of Einstein-Podolsky-Rosen)
Regular string-like braneworlds
In this work, we propose a new class of smooth thick string-like braneworld
in six dimensions. The brane exhibits a varying brane-tension and an
asymptotic behavior. The brane-core geometry is parametrized by the Bulk
cosmological constant, the brane width and by a geometrical deformation
parameter. The source satisfies the dominant energy condition for the
undeformed solution and has an exotic asymptotic regime for the deformed
solution. This scenario provides a normalized massless Kaluza-Klein mode for
the scalar, gravitational and gauge sectors. The near-brane geometry allows
massive resonant modes at the brane for the state and nearby the brane for
.Comment: 14 pages, 12 figures. Some modifications to match the published
version in EPJ
Bilinear and quadratic Hamiltonians in two-mode cavity quantum electrodynamics
In this work we show how to engineer bilinear and quadratic Hamiltonians in
cavity quantum electrodynamics (QED) through the interaction of a single driven
two-level atom with cavity modes. The validity of the engineered Hamiltonians
is numerically analyzed even considering the effects of both dissipative
mechanisms, the cavity field and the atom. The present scheme can be used, in
both optical and microwave regimes, for quantum state preparation, the
implementation of quantum logical operations, and fundamental tests of quantum
theory.Comment: 11 pages, 3 figure
Significance of Ghost Orbit Bifurcations in Semiclassical Spectra
Gutzwiller's trace formula for the semiclassical density of states in a
chaotic system diverges near bifurcations of periodic orbits, where it must be
replaced with uniform approximations. It is well known that, when applying
these approximations, complex predecessors of orbits created in the bifurcation
("ghost orbits") can produce pronounced signatures in the semiclassical spectra
in the vicinity of the bifurcation. It is the purpose of this paper to
demonstrate that these ghost orbits themselves can undergo bifurcations,
resulting in complex, nongeneric bifurcation scenarios. We do so by studying an
example taken from the Diamagnetic Kepler Problem, viz. the period quadrupling
of the balloon orbit. By application of normal form theory we construct an
analytic description of the complete bifurcation scenario, which is then used
to calculate the pertinent uniform approximation. The ghost orbit bifurcation
turns out to produce signatures in the semiclassical spectrum in much the same
way as a bifurcation of real orbits would.Comment: 20 pages, 6 figures, LATEX (IOP style), submitted to J. Phys.
Nonadiabatic coherent evolution of two-level systems under spontaneous decay
In this paper we extend current perspectives in engineering reservoirs by
producing a time-dependent master equation leading to a nonstationary
superposition equilibrium state that can be nonadiabatically controlled by the
system-reservoir parameters. Working with an ion trapped inside a nonindeal
cavity we first engineer effective Hamiltonians that couple the electronic
states of the ion with the cavity mode. Subsequently, two classes of
decoherence-free evolution of the superposition of the ground and decaying
excited levels are achieved: those with time-dependent azimuthal or polar
angle. As an application, we generalise the purpose of an earlier study [Phys.
Rev. Lett. 96, 150403 (2006)], showing how to observe the geometric phases
acquired by the protected nonstationary states even under a nonadiabatic
evolution.Comment: 5 pages, no figure
Order-Parameter Flow in the SK Spin-Glass II: Inclusion of Microscopic Memory Effects
We develop further a recent dynamical replica theory to describe the dynamics
of the Sherrington-Kirkpatrick spin-glass in terms of closed evolution
equations for macroscopic order parameters. We show how microscopic memory
effects can be included in the formalism through the introduction of a dynamic
order parameter function: the joint spin-field distribution. The resulting
formalism describes very accurately the relaxation phenomena observed in
numerical simulations, including the typical overall slowing down of the flow
that was missed by the previous simple two-parameter theory. The advanced
dynamical replica theory is either exact or a very good approximation.Comment: same as original, but this one is TeXabl
On the Stability of the Mean-Field Glass Broken Phase under Non-Hamiltonian Perturbations
We study the dynamics of the SK model modified by a small non-hamiltonian
perturbation. We study aging, and we find that on the time scales investigated
by our numerical simulations it survives a small perturbation (and is destroyed
by a large one). If we assume we are observing a transient behavior the scaling
of correlation times versus the asymmetry strength is not compatible with the
one expected for the spherical model. We discuss the slow power law decay of
observable quantities to equilibrium, and we show that for small perturbations
power like decay is preserved. We also discuss the asymptotically large time
region on small lattices.Comment: 34 page
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