182 research outputs found
Effects of classical stochastic webs on the quantum dynamics of cold atomic gases in a moving optical lattice
We introduce and investigate a system that uses temporal resonance-induced
phase space pathways to create strong coupling between an atomic Bose-Einstein
condensate and a traveling optical lattice potential. We show that these
pathways thread both the classical and quantum phase space of the atom cloud,
even when the optical lattice potential is arbitrarily weak. The topology of
the pathways, which form web-like patterns, can by controled by changing the
amplitude and period of the optical lattice. In turn, this control can be used
to increase and limit the BEC's center-of-mass kinetic energy to pre-specified
values. Surprisingly, the strength of the atom-lattice interaction and
resulting BEC heating of the center-of-mass motion is enhanced by the repulsive
inter-atomic interactions.Comment: 8 pages, 7 figure
Resonant control of cold-atom transport through two optical lattices with a constant relative speed
We show theoretically that the dynamics of cold atoms in the lowest energy
band of a stationary optical lattice can be transformed and controlled by a
second, weaker, periodic potential moving at a constant speed along the axis of
the stationary lattice. The atom trajectories exhibit complex behavior, which
depends sensitively on the amplitude and speed of the propagating lattice. When
the speed and amplitude of the moving potential are low, the atoms are dragged
through the static lattice and perform drifting orbits with frequencies an
order of magnitude higher than that corresponding to the moving potential.
Increasing either the speed or amplitude of the moving lattice induces
Bloch-like oscillations within the energy band of the static lattice, which
exhibit complex resonances at critical values of the system parameters. In some
cases, a very small change in these parameters can reverse the atom's direction
of motion. In order to understand these dynamics we present an analytical
model, which describes the key features of the atom transport and also
accurately predicts the positions of the resonant features in the atom's phase
space. The abrupt controllable transitions between dynamical regimes, and the
associated set of resonances, provide a mechanism for transporting atoms
between precise locations in a lattice: as required for using cold atoms to
simulate condensed matter or as a stepping stone to quantum information
processing. The system also provides a direct quantum simulator of acoustic
waves propagating through semiconductor nanostructures in sound analogs of the
optical laser (SASER)
Exploiting soliton decay and phase fluctuations in atom chip interferometry of Bose-Einstein condensates
We show that the decay of a soliton into vortices provides a mechanism for
measuring the initial phase difference between two merging Bose-Einstein
condensates. At very low temperatures, the mechanism is resonant, operating
only when the clouds start in anti-phase. But at higher temperatures, phase
fluctuations trigger vortex production over a wide range of initial relative
phase, as observed in recent experiments at MIT. Choosing the merge time to
maximize the number of vortices created makes the interferometer highly
sensitive to spatially varying phase patterns and hence atomic movement.Comment: 5 pages, 5 figure
Origin of strong scarring of wavefunctions in quantum wells in a tilted magnetic field
The anomalously strong scarring of wavefunctions found in numerical studies
of quantum wells in a tilted magnetic field is shown to be due to special
properties of the classical dynamics of this system. A certain subset of
periodic orbits are identified which are nearly stable over a very large
interval of variation of the classical dynamics; only this subset are found to
exhibit strong scarring. Semiclassical arguments shed further light on why
these orbits dominate the experimentally observed tunneling spectra.Comment: RevTeX, 5 page
Quantifying Finite Temperature Effects in Atom Chip Interferometry of Bose-Einstein Condensates
We quantify the effect of phase fluctuations on atom chip interferometry of
Bose-Einstein condensates. At very low temperatures, we observe small phase
fluctuations, created by mean-field depletion, and a resonant production of
vortices when the two clouds are initially in anti-phase. At higher
temperatures, we show that the thermal occupation of Bogoliubov modes makes
vortex production vary smoothly with the initial relative phase difference
between the two atom clouds. We also propose a technique to observe vortex
formation directly by creating a weak link between the two clouds. The position
and direction of circulation of the vortices is subsequently revealed by kinks
in the interference fringes produced when the two clouds expand into one
another. This procedure may be exploited for precise force measurement or
motion detection.Comment: 7 pages, 5 figure
Reactive self-heating model of aluminum spherical nanoparticles
Aluminum-oxygen reaction is important in many highly energetic, high pressure
generating systems. Recent experiments with nanostructured thermites suggest
that oxidation of aluminum nanoparticles occurs in a few microseconds. Such
rapid reaction cannot be explained by a conventional diffusion-based mechanism.
We present a rapid oxidation model of a spherical aluminum nanoparticle, using
Cabrera-Mott moving boundary mechanism, and taking self-heating into account.
In our model, electric potential solves the nonlinear Poisson equation. In
contrast with the Coulomb potential, a "double-layer" type solution for the
potential and self-heating leads to enhanced oxidation rates. At maximal
reaction temperature of 2000 C, our model predicts overall oxidation time scale
in microseconds range, in agreement with experimental evidence.Comment: submitte
Spontaneous creation of non-zero angular momentum modes in tunnel-coupled two-dimensional degenerate Bose gases
We investigate the dynamics of two tunnel-coupled two-dimensional degenerate
Bose gases. The reduced dimensionality of the clouds enables us to excite
specific angular momentum modes by tuning the coupling strength, thereby
creating striking patterns in the atom density profile. The extreme sensitivity
of the system to the coupling and initial phase difference results in a rich
variety of subsequent dynamics, including vortex production, complex
oscillations in relative atom number and chiral symmetry breaking due to
counter-rotation of the two clouds.Comment: 7 pages, 5 figure
Atom chips with two-dimensional electron gases: theory of near surface trapping and ultracold-atom microscopy of quantum electronic systems
We show that current in a two-dimensional electron gas (2DEG) can trap
ultracold atoms m away with orders of magnitude less spatial noise than
a metal trapping wire. This enables the creation of hybrid systems, which
integrate ultracold atoms with quantum electronic devices to give extreme
sensitivity and control: for example, activating a single quantized conductance
channel in the 2DEG can split a Bose-Einstein condensate (BEC) for atom
interferometry. In turn, the BEC offers unique structural and functional
imaging of quantum devices and transport in heterostructures and graphene.Comment: 5 pages, 4 figures, minor change
Semiclassical theory of magnetotransport through a chaotic quantum well
We develop a quantitative semiclassical formula for the resonant tunneling
current through a quantum well in a tilted magnetic field. It is shown that the
current depends only on periodic orbits within the quantum well. The theory
explains the puzzling evolution of the tunneling spectra near a tilt angle of
as arising from an exchange bifurcation of the relevant periodic
orbits.Comment: 4 pages, RevTeX, epsf, 2 PostScript Figures (1 with color
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