16,160 research outputs found
Gradient Symplectic Algorithms for Solving the Radial Schrodinger Equation
The radial Schrodinger equation for a spherically symmetric potential can be
regarded as a one dimensional classical harmonic oscillator with a
time-dependent spring constant. For solving classical dynamics problems,
symplectic integrators are well known for their excellent conservation
properties. The class of {\it gradient} symplectic algorithms is particularly
suited for solving harmonic oscillator dynamics. By use of Suzuki's rule for
decomposing time-ordered operators, these algorithms can be easily applied to
the Schrodinger equation. We demonstrate the power of this class of gradient
algorithms by solving the spectrum of highly singular radial potentials using
Killingbeck's method of backward Newton-Ralphson iterations.Comment: 19 pages, 10 figure
Efficient creation of molecules from a cesium Bose-Einstein condensate
We report a new scheme to create weakly bound Cs molecules from an atomic
Bose-Einstein condensate. The method is based on switching the magnetic field
to a narrow Feshbach resonance and yields a high atom-molecule conversion
efficiency of more than 30%, a factor of three higher than obtained with
conventional magnetic-field ramps. The Cs molecules are created in a single
-wave rotational quantum state. The observed dependence of the conversion
efficiency on the magnetic field and atom density shows scattering processes
beyond two-body coupling to occur in the vicinity of the Feshbach resonance.Comment: 7 pages, 4 figures, submitted to Europhysics Letter
Transition from KPZ to Tilted Interface Critical Behavior in a Solvable Asymmetric Avalanche Model
We use a discrete-time formulation to study the asymmetric avalanche process
[Phys. Rev. Lett. vol. 87, 084301 (2001)] on a finite ring and obtain an exact
expression for the average avalanche size of particles as a function of
toppling probabilities depending on parameters and . By mapping
the model below and above the critical line onto driven interface problems, we
show how different regimes of avalanches may lead to different types of
critical interface behavior characterized by either annealed or quenched
disorders and obtain exactly the related critical exponents which violate a
well-known scaling relation when .Comment: 10 page
Exploring the BEC-BCS Crossover with an Ultracold Gas of Li Atoms
We present an overview of our recent measurements on the crossover from a
Bose-Einstein condensate of molecules to a Bardeen-Cooper-Schrieffer
superfluid. The experiments are performed on a two-component spin-mixture of
Li atoms, where a Fesh\-bach resonance serves as the experimental key to
tune the s-wave scattering length and thus to explore the various interaction
regimes. In the BEC-BCS crossover, we have characterized the interaction energy
by measuring the size of the trapped gas, we have studied collective excitation
modes, and we have observed the pairing gap. Our observations provide strong
evidence for superfluidity in the strongly interacting Fermi gas.Comment: Proceedings of ICAP-2004 (Rio de Janeiro). Review on Innsbruck
BEC-BCS crossover experiments with updated Feshbach resonance positio
Off-diagonal correlations in a one-dimensional gas of dipolar bosons
We present a quantum Monte Carlo study of the one-body density matrix (OBDM)
and the momentum distribution of one-dimensional dipolar bosons, with dipole
moments polarized perpendicular to the direction of confinement. We observe
that the long-range nature of the dipole interaction has dramatic effects on
the off-diagonal correlations: although the dipoles never crystallize, the
system goes from a quasi-condensate regime at low interactions to a regime in
which quasi-condensation is discarded, in favor of quasi-solidity. For all
strengths of the dipolar interaction, the OBDM shows an oscillatory behavior
coexisting with an overall algebraic decay; and the momentum distribution shows
sharp kinks at the wavevectors of the oscillations, (where
is the atom density), beyond which it is strongly suppressed. This
\emph{momentum filtering} effect introduces a characteristic scale in the
momentum distribution, which can be arbitrarily squeezed by lowering the atom
density. This shows that one-dimensional dipolar Bose gases, realized e.g. by
trapped dipolar molecules, show strong signatures of the dipolar interaction in
time-of-flight measurements.Comment: 10 pages, 6 figures. v2: fixed a mistake in the comparison with Ref.
9, as well as several typos. Published versio
Surface location of sodium atoms attached to He-3 nanodroplets
We have experimentally studied the electronic excitation of
Na atoms attached to He droplets by means of laser-induced fluorescence as
well as beam depletion spectroscopy. From the similarities of the spectra
(width/shift of absorption lines) with these of Na on He droplets, we
conclude that sodium atoms reside in a ``dimple'' on the droplet surface. The
experimental results are supported by Density Functional calculations at zero
temperature, which confirm the surface location of sodium on He droplets,
and provide a microscopic description of the ``dimple'' structure.Comment: 4 pages, 5 figure
Observation of the Pairing Gap in a Strongly Interacting Fermi Gas
We study fermionic pairing in an ultracold two-component gas of Li atoms
by observing an energy gap in the radio-frequency excitation spectra. With
control of the two-body interactions via a Feshbach resonance we demonstrate
the dependence of the pairing gap on coupling strength, temperature, and Fermi
energy. The appearance of an energy gap with moderate evaporative cooling
suggests that our full evaporation brings the strongly interacting system deep
into a superfluid state.Comment: 18 pages, 3 figure
Precision Measurements of Collective Oscillations in the BEC-BCS Crossover
We report on precision measurements of the frequency of the radial
compression mode in a strongly interacting, optically trapped Fermi gas of Li-6
atoms. Our results allow for a test of theoretical predictions for the equation
of state in the BEC-BCS crossover. We confirm recent quantum Monte-Carlo
results and rule out simple mean-field BCS theory. Our results show the
long-sought beyond-mean-field effects in the strongly interacting BEC regime.Comment: improved discussion of small ellipticity and anharmonicity
correction
Phase-dependent exciton transport and energy harvesting from thermal environments
Non-Markovian effects in the evolution of open quantum systems have recently
attracted widespread interest, particularly in the context of assessing the
efficiency of energy and charge transfer in nanoscale biomolecular networks and
quantum technologies. With the aid of many-body simulation methods, we uncover
and analyse an ultrafast environmental process that causes energy relaxation in
the reduced system to depend explicitly on the phase relation of the initial
state preparation. Remarkably, for particular phases and system parameters, the
net energy flow is uphill, transiently violating the principle of detailed
balance, and implying that energy is spontaneously taken up from the
environment. A theoretical analysis reveals that non-secular contributions,
significant only within the environmental correlation time, underlie this
effect. This suggests that environmental energy harvesting will be observable
across a wide range of coupled quantum systems.Comment: 5 + 4 pages, 3 + 2 figures. Comments welcom
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