172 research outputs found
Confinement-induced resonances for a two-component ultracold atom gas in arbitrary quasi-one-dimensional traps
We solve the two-particle s-wave scattering problem for ultracold atom gases
confined in arbitrary quasi-one-dimensional trapping potentials, allowing for
two different atom species. As a consequence, the center-of-mass and relative
degrees of freedom do not factorize. We derive bound-state solutions and obtain
the general scattering solution, which exhibits several resonances in the 1D
scattering length induced by the confinement. We apply our formalism to two
experimentally relevant cases: (i) interspecies scattering in a two-species
mixture, and (ii) the two-body problem for a single species in a non-parabolic
trap.Comment: 22 pages, 3 figure
Quasienergy description of the driven Jaynes-Cummings model
We analyze the driven resonantly coupled Jaynes-Cummings model in terms of a
quasienergy approach by switching to a frame rotating with the external
modulation frequency and by using the dressed atom picture. A quasienergy
surface in phase space emerges whose level spacing is governed by a rescaled
effective Planck constant. Moreover, the well-known multiphoton transitions can
be reinterpreted as resonant tunneling transitions from the local maximum of
the quasienergy surface. Most importantly, the driving defines a quasienergy
well which is nonperturbative in nature. The quantum mechanical quasienergy
state localized at its bottom is squeezed. In the Purcell limited regime, the
potential well is metastable and the effective local temperature close to its
minimum is uniquely determined by the squeezing factor. The activation occurs
in this case via dressed spin flip transitions rather than via quantum
activation as in other driven nonlinear quantum systems such as the quantum
Duffing oscillator. The local maximum is in general stable. However, in
presence of resonant coherent or dissipative tunneling transitions the system
can escape from it and a stationary state arises as a statistical mixture of
quasienergy states being localized in the two basins of attraction. This gives
rise to a resonant or an antiresonant nonlinear response of the cavity at
multiphoton transitions. The model finds direct application in recent
experiments with a driven superconducting circuit QED setup.Comment: 13 pages, 8 fi
All-optical trapping and acceleration of heavy particles
A scheme for fast, compact, and controllable acceleration of heavy particles
in vacuum is proposed, in which two counterpropagating lasers with variable
frequencies drive a beat-wave structure with variable phase velocity, thus
allowing for trapping and acceleration of heavy particles, such as ions or
muons. Fine control over the energy distribution and the total charge of the
beam is obtained via tuning of the frequency variation. The acceleration scheme
is described with a one-dimensional theory, providing the general conditions
for trapping and scaling laws for the relevant features of the particle beam.
Two-dimensional, electromagnetic particle-in-cell simulations confirm the
validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic
Prospects for all-optical ultrafast muon acceleration
A scheme for fast, compact, and controllable acceleration of heavy particles
in vacuum has been recently proposed [F. Peano et al., New J. Phys. 10 033028
(2008)], wherein two counterpropagating laser beams with variable frequencies
drive a beat-wave structure with variable phase velocity, leading to particle
trapping and acceleration. The technique allows for fine control over the
energy distribution and the total charge of the accelerated beam, to be
obtained via tuning of the frequency variation. Here, the theoretical bases of
the acceleration scheme are described, and the possibility of applications to
ultrafast muon acceleration and to the prompt extraction of cold-muon beams is
discussed.Comment: 12 pages, 5 figures, to appear in Plasma Physics and Controlled
Fusio
Qubit state detection using the quantum Duffing oscillator
We introduce a detection scheme for the state of a qubit, which is based on
resonant few-photon transitions in a driven nonlinear resonator. The latter is
parametrically coupled to the qubit and is used as its detector. Close to the
fundamental resonator frequency, the nonlinear resonator shows sharp resonant
few-photon transitions. Depending on the qubit state, these few-photon
resonances are shifted to different driving frequencies. We show that this
detection scheme offers the advantage of small back action, a large
discrimination power with an enhanced read-out fidelity, and a sufficiently
large measurement efficiency. A realization of this scheme in the form of a
persistent current qubit inductively coupled to a driven SQUID detector in its
nonlinear regime is discussed.Comment: 10 pages, 6 figures. To appear in Phys. Rev.
Expansion of nanoplasmas and laser-driven nuclear fusion in single exploding clusters
The expansion of laser-irradiated clusters or nanodroplets depends strongly
on the amount of energy delivered to the electrons and can be controlled by
using appropriately shaped laser pulses. In this paper, a self-consistent
kinetic model is used to analyze the transition from quasineutral,
hydrodinamic-like expansion regimes to the Coulomb explosion (CE) regime when
increasing the ratio between the thermal energy of the electrons and the
electrostatic energy stored in the cluster. It is shown that a suitable
double-pump irradiation scheme can produce hybrid expansion regimes, wherein a
slow hydrodynamic expansion is followed by a fast CE, leading to ion overtaking
and producing multiple ion flows expanding with different velocities. This can
be exploited to obtain intracluster fusion reactions in both homonuclear
deuterium clusters and heteronuclear deuterium-tritium clusters, as also proved
by three-dimensional molecular-dynamics simulations.Comment: 9 pages, 3 figures, to appear in Plasma Physics and Controlled Fusio
Adaptive Refinements in BEM
Accuracy estimates and adaptive refinements is nowadays one of the main research topics in finite element computations [6,7,8, 9,11].Its extension to Boundary Elements has been tried as a means to better understand its capabilities as well as to impro ve its efficiency and its obvious advantages. The possibility of implementing adaptive techniques was shown [1,2] for h-conver gence and p-convergence respectively. Some posterior works [3,4 5,10] have shown the promising results that can be expected from those techniques. The main difficulty is associated to the reasonable establishment of “estimation” and “indication” factors related to the global and local errors in each refinement. Although some global measures have been used it is clear that the reduction in dimension intrinsic to boundary elements (3D→2D: 2D→1D) could allow a direct comparison among residuals using the graphic possibilities of modern computers and allowing a point-to-point comparison in place of the classical global approaches. Nevertheless an indicator generalizing the well known Peano’s one has been produced
Nonlinear response of a driven vibrating nanobeam in the quantum regime
We analytically investigate the nonlinear response of a damped doubly clamped
nanomechanical beam under static longitudinal compression which is excited to
transverse vibrations. Starting from a continuous elasticity model for the
beam, we consider the dynamics of the beam close to the Euler buckling
instability. There, the fundamental transverse mode dominates and a quantum
mechanical time-dependent effective single particle Hamiltonian for its
amplitude can be derived. In addition, we include the influence of a
dissipative Ohmic or super-Ohmic environment. In the rotating frame, a
Markovian master equation is derived which includes also the effect of the
time-dependent driving in a non-trivial way. The quasienergies of the pure
system show multiple avoided level crossings corresponding to multiphonon
transitions in the resonator. Around the resonances, the master equation is
solved analytically using Van Vleck perturbation theory. Their lineshapes are
calculated resulting in simple expressions. We find the general solution for
the multiple multiphonon resonances and, most interestingly, a bath-induced
transition from a resonant to an antiresonant behavior of the nonlinear
response.Comment: 25 pages, 5 figures, submitted to NJ
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