4,606 research outputs found
Metal-Insulator Transition Revisited for Cold Atoms in Non-Abelian Gauge Potentials
We discuss the possibility of realizing metal-insulator transitions with
ultracold atoms in two-dimensional optical lattices in the presence of
artificial gauge potentials. Such transitions have been extensively studied for
magnetic fields corresponding to Abelian gauges; they occur when the magnetic
flux penetrating the lattice plaquette is an irrational multiple of the
magnetic flux quantum. Here we present the first study of these transitions for
non-Abelian U(2) gauge fields, which can be realized with atoms with two pairs
of degenerate internal states. In contrast to the Abelian case, the spectrum
and localization transition in the non-Abelian case is strongly influenced by
atomic momenta. In addition to determining the localization boundary, the
momentum fragments the spectrum and the minimum energy viewed as a function of
momentum exhibits a step structure. Other key characteristics of the
non-Abelian case include the absence of localization for certain states and
satellite fringes around the Bragg peaks in the momentum distribution and an
interesting possibility that the transition can be tuned by the atomic momenta.Comment: 4 pages, 4 figures, see http://physics.gmu.edu/~isatija/recentpub.htm
for high resolution figure
Generalized Thermalization in an Integrable Lattice System
After a quench, observables in an integrable system may not relax to the
standard thermal values, but can relax to the ones predicted by the generalized
Gibbs ensemble (GGE) [M. Rigol et al., Phys. Rev. Lett. 98, 050405 (2007)]. The
GGE has been shown to accurately describe observables in various
one-dimensional integrable systems, but the origin of its success is not fully
understood. Here we introduce a microcanonical version of the GGE and provide a
justification of the GGE based on a generalized interpretation of the
eigenstate thermalization hypothesis, which was previously introduced to
explain thermalization of nonintegrable systems. We study relaxation after a
quench of one-dimensional hard-core bosons in an optical lattice. Exact
numerical calculations for up to 10 particles on 50 lattice sites (~10^10
eigenstates) validate our approach.Comment: 8 pages, 9 figures, as publishe
The Summons to Adventure in Our Modern Life
Commencement address given by Charles Clark Stillman, Director, School of Social Administration, Ohio State University, to the Autumn 1938 graduating class of The Ohio State University, University Hall Auditorium, Columbus, Ohio, December 21, 1938
Frequency-dependent polarizabilities of alkali atoms from ultraviolet through infrared spectral regions
We present results of first-principles calculations of the
frequency-dependent polarizabilities of all alkali atoms for light in the
wavelength range 300-1600 nm, with particular attention to wavelengths of
common infrared lasers. We parameterize our results so that they can be
extended accurately to arbitrary wavelengths above 800 nm. This work is
motivated by recent experiments involving simultaneous optical trapping of two
different alkali species. Our data can be used to predict the oscillation
frequencies of optically-trapped atoms, and particularly the ratios of
frequencies of different species held in the same trap. We identify wavelengths
at which two different alkali atoms have the same oscillation frequency.Comment: 6 pages, 2 figure
State-insensitive bichromatic optical trapping
We propose a scheme for state-insensitive trapping of neutral atoms by using
light with two independent wavelengths. In particular, we describe the use of
trapping and control lasers to minimize the variance of the potential
experienced by a trapped Rb atom in ground and excited states. We present
calculated values of wavelength pairs for which the 5s and 5p_{3/2} levels have
the same ac Stark shifts in the presence of two laser fields.Comment: 5 pages, 4 figure
Momentum-space engineering of gaseous Bose-Einstein condensates
We show how the momentum distribution of gaseous Bose--Einstein condensates
can be shaped by applying a sequence of standing-wave laser pulses. We present
a theory, whose validity for was demonstrated in an earlier experiment [L.\
Deng, et al., \prl {\bf 83}, 5407 (1999)], of the effect of a two-pulse
sequence on the condensate wavefunction in momentum space. We generalize the
previous result to the case of pulses of arbitrary intensity separated by
arbitrary intervals and show how these parameters can be engineered to produce
a desired final momentum distribution. We find that several momentum
distributions, important in atom-interferometry applications, can be engineered
with high fidelity with two or three pulses.Comment: 13 pages, 4 figure
Probing the circulation of ring-shaped Bose-Einstein condensates
This paper reports the results of a theoretical and experimental study of how
the initial circulation of ring-shaped Bose-Einstein condensates (BECs) can be
probed by time-of-flight (TOF) images. We have studied theoretically the
dynamics of a BEC after release from a toroidal trap potential by solving the
3D Gross-Pitaevskii (GP) equation. The trap and condensate characteristics
matched those of a recent experiment. The circulation, experimentally imparted
to the condensate by stirring, was simulated theoretically by imprinting a
linear azimuthal phase on the initial condensate wave function. The theoretical
TOF images were in good agreement with the experimental data. We find that upon
release the dynamics of the ring--shaped condensate proceeds in two distinct
phases. First, the condensate expands rapidly inward, filling in the initial
hole until it reaches a minimum radius that depends on the initial circulation.
In the second phase, the density at the inner radius increases to a maximum
after which the hole radius begins slowly to expand. During this second phase a
series of concentric rings appears due to the interference of ingoing and
outgoing matter waves from the inner radius. The results of the GP equation
predict that the hole area is a quadratic function of the initial circulation
when the condensate is released directly from the trap in which it was stirred
and is a linear function of the circulation if the trap is relaxed before
release. These scalings matched the data. Thus, hole size after TOF can be used
as a reliable probe of initial condensate circulation. This connection between
circulation and hole size after TOF will facilitate future studies of
atomtronic systems that are implemented in ultracold quantum gases.Comment: 9 pages, 9 figure
Accurate determination of electric-dipole matrix elements in K and Rb from Stark shift measurements
Stark shifts of potassium and rubidium D1 lines have been measured with high
precision by Miller et al [1]. In this work, we combine these measurements with
our all-order calculations to determine the values of the electric-dipole
matrix elements for the 4p_j-3d_j' transitions in K and for the 5p_j-4d_j'
transitions in Rb to high precision. The 4p_1/2-3d_3/2 and 5p_1/2-4d_3/2
transitions contribute on the order of 90% to the respective polarizabilities
of the np_1/2 states in K and Rb, and the remaining 10% can be accurately
calculated using the relativistic all-order method. Therefore, the combination
of the experimental data and theoretical calculations allows us to determine
the np-(n-1)d matrix elements and their uncertainties. We compare these values
with our all-order calculations of the np-(n-1)d matrix elements in K and Rb
for a benchmark test of the accuracy of the all-order method for transitions
involving nd states. Such matrix elements are of special interest for many
applications, such as determination of magic wavelengths in alkali-metal atoms
for state-insensitive cooling and trapping and determination of blackbody
radiation shifts in optical frequency standards with ions.Comment: 5 page
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