# Matt's arXiv selection: week ending 29 February 2008.

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Mon, 03 Mar 2008 13:49:02 +1000

Hi all,

There are 27 new preprints, and only 2 replacements it seems.... I hope I
haven't missed any... let me know if I did miss yours.

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arXiv:0802.3211
Date: Thu, 21 Feb 2008 21:18:27 GMT (204kb)

Title: Antiferromagnetic Order of Strongly Interacting Fermions in a Trap:
Real-Space Dynamical Mean-Field Analysis
Authors: M. Snoek, I. Titvinidze, C. Toke, K. Byczuk, and W. Hofstetter
Categories: cond-mat.str-el
\\
We develop and apply a Real-Space Dynamical Mean-Field Theory (R-DMFT)
approach for interacting fermions in an inhomogeneous environment. We apply
this non-perturbative scheme to antiferromagnetic states of repulsively
interacting fermions with spin $\tfrac{1}{2}$ in a harmonic potential. Within
R-DMFT antiferromagnetic order is found to be stable in spatial regions with
total particle density close to one, but persists also in parts of the system
where the local density significantly deviates from half filling. In systems
with spin imbalance, we find that antiferromagnetism is gradually suppressed
and phase separation emerges beyond a critical value of the spin imbalance.
\\ ( http://arxiv.org/abs/0802.3211 , 204kb)
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arXiv:0802.3225
Date: Thu, 21 Feb 2008 21:43:59 GMT (571kb)

Title: Effects of boundaries and density inhomogeneity on states of vortex
matter in Bose--Einstein condensates at finite temperature
Authors: S. Kragset, E. Babaev, A. Sudbo
Categories: cond-mat.stat-mech
Comments: 15 pages, 13 figures. Submitted to Physical Review A. High resolution
pictures will be available in published version
\\
Most of the literature on quantum vortices predicting various states of
vortex matter in three dimensions at finite temperatures in quantum fluids is
based on an assumption of an extended and homogeneous system. It is well known
not to be the case in actual Bose--Einstein condensates in traps which are
finite systems with nonuniform density. This raises the question to what extent
one can speak of different aggregate states of vortex matter (vortex lattices,
liquids and tensionless vortex tangle) in these system. To address this point,
in the present work we focus on the finite-size, boundaries and density
inhomogeneity effects on thermal vortex matter in a Bose--Einstein condensate.
To this end we perform Monte Carlo simulations on a model system describing
trapped Bose--Einstein condensates. Throughout the paper, we draw on analogies
with results for vortex matter obtained for extended systems. This work
suggests that finiteness and intrinsic inhomogeneity of the system not
withstanding, one nonetheless can approximately invoke the notion of distinct
aggregate states of vortex matter realized at certain length scales. This might
be helpful, in particular in search of possible new states of vortex matter in
Bose--Einstein condensates with multiple components and different symmetries.
\\ ( http://arxiv.org/abs/0802.3225 , 571kb)
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arXiv:0802.3262
Date: Fri, 22 Feb 2008 07:20:10 GMT (112kb)

Title: Binding Energies of 6Li p-wave Feshbach Molecules
Authors: J. Fuchs, C. Ticknor, P. Dyke, G. Veeravalli, E. Kuhnle, W. Rowlands,
P. Hannaford, and C. J. Vale
Categories: cond-mat.other
\\
We present measurements of the binding energies of $^6$Li p-wave Feshbach
molecules formed in combinations of the (F = 1/2, m_F = +1/2), (1), and (F =
1/2, m_F = -1/2), (2), states. The binding energies scale linearly with
magnetic field detuning for all three resonances. The relative molecular
magnetic moments are found to be $113 \pm 7 \mu$K/G, $111 \pm 6 \mu$K/G and
$118 \pm 8 \mu$K/G for the (1)-(1), (1)-(2) and (2)-(2) resonances,
respectively, in good agreement with theoretical predictions. Closed channel
amplitudes and the size of the p-wave molecules are obtained theoretically from
full closed-coupled calculations.
\\ ( http://arxiv.org/abs/0802.3262 , 112kb)
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arXiv:0802.3301
Date: Fri, 22 Feb 2008 12:10:50 GMT (367kb)

Title: Suppression of Zeeman splitting and polarization steps in localized
exciton-polariton condensates
Authors: T. C. H. Liew, Yuri G. Rubo, I. A. Shelykh, A. V. Kavokin
Categories: cond-mat.mes-hall
\\
We show that the condensation of exciton-polaritons in semiconductor
microcavities in an applied magnetic field manifests itself in the quenching of
the Zeeman splitting of an elliptically polarized condensate. The circular
polarization degree of a localized condensate with a finite number of particles
increases as a function of the magnetic field with a step-like behavior. The
width of each polarization step is fixed by the polariton-polariton interaction
constants and the number of steps is fixed by the number of polaritons in the
condensate. The magnetic susceptibility of the condensate depends qualitatively
on the parity of the number of polaritons.
\\ ( http://arxiv.org/abs/0802.3301 , 367kb)
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arXiv:0802.3339
Date: Fri, 22 Feb 2008 15:36:37 GMT (24kb)

Title: Synchronized and desynchronized phases of coupled non-equilibrium
exciton-polariton condensates
Authors: Michiel Wouters
Categories: cond-mat.mes-hall
\\
We theoretically analyze the synchronized and desynchronized phases of
coupled non-equilibrium polariton condensates within mean field theory. An
analytical condition for the existence of a synchronized phase is derived for
two coupled wells. The case of many wells in a 2D disordered geometry is
studied numerically. The relation to recent experiments on polariton
condensation in CdTe microcavities is discussed.
\\ ( http://arxiv.org/abs/0802.3339 , 24kb)
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arXiv:0802.3164 (*cross-listing*)
Date: Thu, 21 Feb 2008 17:36:12 GMT (226kb)

Title: A non-Hermitian $PT-$symmetric Bose-Hubbard model: eigenvalue rings from
unfolding higher-order exceptional points
Authors: E. M. Graefe, U. Guenther, H. J. Korsch, A. E. Niederle
Categories: math-ph cond-mat.other math.MP quant-ph
\\
We study a non-Hermitian $PT-$symmetric generalization of an $N$-particle,
two-mode Bose-Hubbard system, modeling for example a Bose-Einstein condensate
in a double well potential coupled to a continuum via a sink in one of the
wells and a source in the other. The effect of the interplay between the
particle interaction and the non-Hermiticity on characteristic features of the
spectrum is analyzed drawing special attention to the occurrence and unfolding
of exceptional points (EPs). We find that for vanishing particle interaction
there are only two EPs of order $N+1$ which under perturbation unfold either
into $[(N+1)/2]$ eigenvalue pairs (and in case of $N+1$ odd, into an additional
zero-eigenvalue) or into eigenvalue triplets (third-order eigenvalue rings) and
$(N+1)\mod 3$ single eigenvalues, depending on the direction of the
perturbation in parameter space. This behavior is described analytically using
perturbational techniques. More general EP unfoldings into eigenvalue rings up
to $(N+1)$th order are indicated.
\\ ( http://arxiv.org/abs/0802.3164 , 226kb)
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arXiv:0802.3351
Date: Fri, 22 Feb 2008 17:24:01 GMT (10kb)

Title: The computational difficulty of finding MPS ground states
Authors: Norbert Schuch, Ignacio Cirac, Frank Verstraete
Categories: quant-ph
\\
We determine the computational difficulty of finding ground states of
one-dimensional (1D) Hamiltonians which are known to be Matrix Product States
(MPS). Therefore, we construct a class of 1D frustration free Hamiltonians with
unique MPS ground states and a polynomial gap above, for which finding the
ground state is at least as hard as factoring. By lifting the requirement of a
unique ground state, we obtain a class for which finding the ground state
solves an NP-complete problem. Therefore, for these Hamiltonians it is not even
possible to certify that the ground state has been found. Our results thus
imply that in order to prove convergence of variational methods over MPS, as
the Density Matrix Renormalization Group, one has to put more requirements than
just MPS ground states and a polynomial spectral gap.
\\ ( http://arxiv.org/abs/0802.3351 , 10kb)
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arXiv:0802.3417
Date: Sat, 23 Feb 2008 02:57:55 GMT (445kb,D)

Title: Reduced density matrices and coherence of trapped interacting bosons
Authors: Kaspar Sakmann, Alexej I. Streltsov, Ofir E. Alon, and Lorenz S.
Cederbaum
Categories: cond-mat.other
\\
The first- and second-order correlation functions of trapped, interacting
Bose-Einstein condensates are investigated numerically on a many-body level
from first principles. Correlations in real space and momentum space are
treated. The coherence properties are analyzed. The results are obtained by
solving the many-body Schr\"odinger equation. It is shown in an example how
many-body effects can be induced by the trap geometry. A generic fragmentation
scenario of a condensate is considered. The correlation functions are discussed
along a pathway from a single condensate to a fragmented condensate. It is
shown that strong correlations can arise from the geometry of the trap, even at
weak interaction strengths. The natural orbitals and natural geminals of the
system are obtained and discussed. It is shown how the fragmentation of the
condensate can be understood in terms of its natural geminals. The many-body
results are compared to those of mean-field theory. The best solution within
mean-field theory is obtained. The limits in which mean-field theories are
valid are determined. In these limits the behavior of the correlation functions
is explained within an analytical model.
\\ ( http://arxiv.org/abs/0802.3417 , 445kb)
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arXiv:0802.3587
Date: Mon, 25 Feb 2008 10:20:48 GMT (431kb)

Title: Roton-like mode in solid He-4
Authors: E. Blackburn, S. K. Sinha, C. Broholm, J. R. D. Copley, R. W. Erwin
and J. M. Goodkind
Categories: cond-mat.stat-mech
Comments: 7 pages, 5 figures, 1 table
\\
Recent theoretical and experimental work on solid He-4 has focused on
vacancies, or other lattice defects and whether these can form a Bose-Einstein
condensate within the solid. The earliest suggestion that this could happen was
based on the conjecture that the ground state of the solid at T = 0 K would
include vacancies. Although no direct evidence for zero point vacancies has
been presented, a variety of experimental observations have been interpreted as
being due to thermally activated vacancies. Here we directly probe the
excitation spectrum of hcp solid He-4 using inelastic neutron scattering. We
identify a branch of delocalized excitations, with both longitudinal and
transverse dispersion that coexist with acoustic phonons. While the energy gap
is larger and the characteristic wavevector is shifted to coincide with the
position of the (100) Bragg peak, the longitudinal effective mass of this mode
is within 15% of that for rotons in superfluid He-4. The dispersion relation
intersects the longitudinal acoustic phonon half way to the zone boundary, and
this distinguishes the mode from a conventional optic phonon. Our results
provide direct evidence for coherent delocalized non-phonon excitations in
solid helium, which we identify as delocalized vacancy modes.
\\ ( http://arxiv.org/abs/0802.3587 , 431kb)
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arXiv:0802.3687
Date: Mon, 25 Feb 2008 20:06:49 GMT (265kb)

Title: The single-atom box: bosonic staircase and effects of parity
Authors: D.V. Averin, T. Bergeman, P.R. Hosur, and C. Bruder
Categories: cond-mat.mes-hall
Comments: 5 pages, 4 included figues
\\
We have developed a theory of a Josephson junction formed by two
tunnel-coupled Bose-Einstein condensates in a double-well potential in the
regime of strong atom-atom interaction for an arbitrary total number $N$ of
bosons in the condensates. The tunnel resonances in the junction are shown to
be periodically spaced by the interaction energy, forming a single-atom
staircase sensitive to the parity of $N$ even for large $N$. One of the
manifestations of the staircase structure is the periodic modulation with the
bias energy of the visibility of the interference pattern in lattices of
junctions.
\\ ( http://arxiv.org/abs/0802.3687 , 265kb)
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arXiv:0802.3392
Date: Fri, 22 Feb 2008 21:20:07 GMT (26kb)

Title: Single-atom aided probe of the decoherence of a Bose-Einstein condensate
Authors: H. T. Ng and S. Bose
Categories: quant-ph
\\
We study a two-level atom coupled to a Bose-Einstein condensate. We show that
the rules governing the decoherence of mesoscopic superpositions involving
different classical-like states of the condensate can be probed using this
system. This scheme is applicable irrespective of whether the condensate is
initially in a coherent, thermal or more generally in any mixture of coherent
states. The effects of atom loss and finite temperature to the decoherence can
therefore be studied. We also discuss the various noise sources causing the
decoherence.
\\ ( http://arxiv.org/abs/0802.3392 , 26kb)
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arXiv:0802.3503
Date: Sun, 24 Feb 2008 11:27:46 GMT (281kb)

Title: Controlling subluminal to superluminal behavior of group velocity in an
f-deformed Bose-Einstein condensate beyond the rotating wave approximation
Authors: Z. Haghshenasfard, M. Soltanolkotabi and M. H. Naderi
Categories: quant-ph
\\
In this paper, we investigate tunable control of the group velocity of a weak
probe field propagating through an f-deformed Bose-Einstein condensate of
three-level atoms beyond the rotating wave approximation. For this purpose, we
use an f- deformed generalization of an effective two-level quantum model of
the three-level configuration without the rotating wave approximation in which
the Gardiners phonon operators for Bose-Einstein condensate are deformed by an
operator- valued function,f(n), of the particle- number operator n .
Corrections produced by the counter- rotating terms appear in the first order
as an intensity- dependent detuning and in the second order as an intensity-
dependent atom-field coupling. We consider the collisions between the atoms as
a special kind of f- deformation where the collision rate k is regarded as the
deformation parameter. We demonstrate the enhanced effect of subluminal and
superluminal propagation based on electromagnetically induced transparency and
electromagnetically induced absorption, respectively. In particular, we find
that (i) the absorptive and dispersive properties of the deformed condensate
can be controlled effectively in the absence of the rotating wave approximation
by changing the deformation parameter k, the total number of atoms N and the
counter- rotating terms parameter, (ii) by increasing the values of k, 1/N and
the counter- rotating terms parameter, the group velocity of the probe pulse
changes, from subluminal to superluminal and (iii) beyond the rotating wave
approximation, the subluminal and superluminal behaviors of the probe field are
enhanced.
\\ ( http://arxiv.org/abs/0802.3503 , 281kb)
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arXiv:0802.3601
Date: Mon, 25 Feb 2008 11:39:15 GMT (67kb)

Title: Auxiliary fields as a tool for computing analytical solutions of the
Schr\"{o}dinger equation
Authors: B. Silvestre-Brac, C. Semay, F. Buisseret
Categories: quant-ph
\\
We propose a new method to obtain approximate solutions for the
Schr\"{o}dinger equation with an arbitrary potential that possesses bound
states. This method, relying on the auxiliary field technique, allows in many
cases to find analytical solutions. It offers a convenient way to study the
qualitative features of the energy spectrum of bound states in any potential.
In particular, we illustrate our method by solving the case of central
potentials with power-law form and with logarithmic form. For these types of
potentials, we propose very accurate analytical energy formulae which improve a
lot the corresponding formulae that can be found in literature.
\\ ( http://arxiv.org/abs/0802.3601 , 67kb)
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arXiv:0802.3774
Date: Tue, 26 Feb 2008 09:37:36 GMT (646kb)

Title: The quasi-periodic Bose-Hubbard model and localization in
one-dimensional cold atomic gases
Authors: G. Roux, T. Barthel, I. P. McCulloch, C. Kollath, U. Schollwoeck, T.
Giamarchi
Categories: cond-mat.str-el cond-mat.dis-nn
\\
We compute the phase diagram of the one-dimensional Bose-Hubbard model with a
quasi-periodic potential by means of the density-matrix renormalization group
technique. This model describes the physics of cold atoms loaded in an optical
lattice in the presence of a superlattice potential whose wave length is
incommensurate with the main lattice wave length. After discussing the
conditions under which the model can be realized experimentally, the study of
the density vs. the chemical potential curves for a non-trapped system uncovers
the existence of gapped phases for incommensurate densities interpreted as
incommensurate charge-density wave phases. Furthermore, a localization
transition is known to occur above a critical value of the potential depth V2
in the case of free and hard-core bosons. We extend these results to soft-core
bosons for which the phase diagrams at fixed density display new features
compared with the phase diagram known for a random box distribution disorder.
In particular, a direct transition from the superfluid phase to the Mott
insulating phase is found at finite V2. Evidences for reentrances of the
superfluid phase upon increasing interactions are presented. We finally comment
on different ways to probe the occuring quantum phases and most importantly the
existence of a critical value for the localization transition. The later
feature can be investigated by looking at the expansion of the cloud after
releasing the trap.
\\ ( http://arxiv.org/abs/0802.3774 , 646kb)
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arXiv:0802.3794
Date: Tue, 26 Feb 2008 11:46:54 GMT (101kb)

Title: On the Reflection and Refraction of Bose-condensate Excitations
Authors: Shohei Watabe and Yusuke Kato
Categories: cond-mat.other
\\
We investigate the transmission and reflection of Bose-condensate excitations
in the low energy limit across the arbitrary potential barrier separating two
condensates with different densities. The anomalous tunneling named by Kagan et
al. [Yu. Kagan et al., Phys. Rev. Lett., 90 (2003) 130402] is comprehensible in
terms of the impedance matching. The Bogoliubov excitation in the low energy
limit has the incident angle where the perfect transmission occurs. This
condition corresponds to the Brewster's law for the electromagnetic wave. There
also exists the total internal reflection of the Bogoliubov excitation in the
low energy limit.
\\ ( http://arxiv.org/abs/0802.3794 , 101kb)
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arXiv:0802.3808
Date: Tue, 26 Feb 2008 13:23:05 GMT (760kb,D)

Title: Two-channel Feshbach physics in a structured continuum
Authors: N. Nygaard, R. Piil, and K. Molmer
Categories: cond-mat.other
Comments: 17 pages, 9 embedded figures
\\
We analyze the scattering and bound state physics of a pair of atoms in a
one-dimensional optical lattice interacting via a narrow Feshbach resonance.
The lattice provides a structured continuum allowing for the existence of bound
dimer states both below and above the continuum bands, with pairs above the
continuum stabilized by either repulsive interactions or their center of mass
motion. Inside the band the Feshbach coupling to a closed channel bound state
leads to a Fano resonance profile for the transmission, which may be mapped out
by RF- or photodissociative spectroscopy. We generalize the scattering length
concept to the one-dimensional lattice, where a scattering length may be
defined at both the lower and the upper continuum thresholds. As a function of
the applied magnetic field the scattering length at either band edge exhibits
the usual Feshbach divergence when a bound state enters or exits the continuum.
Near the scattering length divergences the binding energy and wavefunction of
the weakly bound dimer state acquires a universal form reminiscent of those of
free-space Feshbach molecules. We give numerical examples of our analytic
results for a specific Feshbach resonance, which has been studied
experimentally.
\\ ( http://arxiv.org/abs/0802.3808 , 760kb)
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arXiv:0802.3818
Date: Tue, 26 Feb 2008 14:45:20 GMT (60kb)

Title: Dynamical Structure Factor and Spin-Density Separation for a
Weakly-Interacting Two-Component Bose Gas
Authors: M.-C. Chung and A. B. Bhattacherjee
Categories: cond-mat.other
\\
We show that spin-density separation in a Bose gas is not restricted to 1D
but also occurs in higher dimension. The ratio ($\alpha$) of the intra-species
atom-atom interaction strength to the inter-species interaction strength,
strongly influences the dynamics of spin-density separation and the elementary
excitations. The density wave is phonon-like for all values of $\alpha$. For
$\alpha<1$, spin wave is also phonon-like. The spin waves have a quadratic
dispersion in the $\alpha=1$ coupling regime, while in the phase separated
regime ($\alpha>1$) the spin waves are found to be damped. The dynamical
structure factor (DSF) reveals two distinct peaks corresponding to the density
and spin waves for $\alpha \le 1$. For $\alpha > 1$ there is only one DSF peak
corresponding to the density wave.
\\ ( http://arxiv.org/abs/0802.3818 , 60kb)
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arXiv:0802.3894
Date: Tue, 26 Feb 2008 20:42:41 GMT (370kb)

Title: Pattern formation in mixtures of ultracold atoms in optical lattices
Authors: M. M. Maska (University of Silesia), R. Lemanski (Institute of Low
Temperature and Structure Research), J. K. Freericks (Georgetown University)
and C. J. Williams (Joint Quantum Institute, National Institute of Standards
and Technology)
Categories: cond-mat.str-el
Comments: 5 pages, 4 figures, typeset in ReVTeX
\\
Regular pattern formation is ubiquitous in nature; it occurs in biological,
physical, and materials science systems. Here we propose a set of experiments
with ultracold atoms that show how to examine different types of pattern
formation. In particular, we show how one can see the analog of labyrinthine
patterns (so-called quantum emulsions) in mixtures of light and heavy atoms
(that tend to phase separate) by tuning the trap potential and we show how
complex geometrically ordered patterns emerge (when the mixtures do not phase
separate), which could be employed for low-temperature thermometry. The complex
physical mechanisms for the pattern formation at zero temperature are
understood within a theoretical analysis called the local density
approximation.
\\ ( http://arxiv.org/abs/0802.3894 , 370kb)
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arXiv:0802.3945
Date: Wed, 27 Feb 2008 02:12:56 GMT (327kb)

Title: Fulde-Ferrell-Larkin-Ovchinnikov oscillations in harmonically trapped
optical lattices
Authors: M. Iskin and C. J. Williams
Categories: cond-mat.supr-con cond-mat.other
Comments: 4 pages with 4 figures
\\
The attractive Fermi-Hubbard Hamiltonian is solved via the Bogoliubov-de
Gennes formalism to analyze the ground state phases of population imbalanced
two-component fermion mixtures in harmonically trapped optical lattices. In the
low density limit, the superfluid order parameter has
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type oscillations in the radial
direction towards the trap edges to accommodate the unpaired fermions that are
pushed away from the trap center with a single peak in their density. However,
in the high density limit, while the order parameter has oscillations in the
radial direction towards the trap center for low imbalances, it also has
oscillations towards the trap edges with increasing imbalance until the
superfluid to normal phase transition occurs beyond a critical imbalance. This
leads to a single peak in the density of unpaired fermions for low and high
imbalances, but leads to double peaks for intermediate imbalances.
\\ ( http://arxiv.org/abs/0802.3945 , 327kb)
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arXiv:0802.3960
Date: Wed, 27 Feb 2008 07:20:12 GMT (985kb)

Title: Symmetry Breaking of Vortex Patterns in a Rotating Harmonic Potential
Authors: H.Sakaguchi and H.Takeshita
Categories: cond-mat.soft cond-mat.supr-con
\\
We numerically study the symmetry breaking instabilities of vortex patterns
in a rotating harmonic potential using a type of Ginzburg-Landau equation. The
configurations of vortex lattices change markedly by the symmetry-breaking
instabilities, and then, some vortices move away from the confinement
potential, which leads to the annihilation of vortices. The symmetry-breaking
instabilities and the instabilities of vortex nucleation determine the
parameter region of stable vortex patterns. We verify that the
symmetry-breaking instabilities also occur in a type of complex Ginzburg-Landau
equation.
\\ ( http://arxiv.org/abs/0802.3960 , 985kb)
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arXiv:0802.4039
Date: Wed, 27 Feb 2008 16:02:57 GMT (408kb)

Title: Theoretical tools for atom laser beam propagation
Authors: J.-F. Riou, Y. Le Coq, F. Impens, W. Guerin, C. J. Bord\'e, A. Aspect,
and P. Bouyer
Categories: cond-mat.other
\\
We present a theoretical model for the propagation of non self-interacting
atom laser beams. We start from a general propagation integral equation, and we
use the same approximations as in photon optics to derive tools to calculate
the atom laser beam propagation. We discuss the approximations that allow to
reduce the general equation whether to a Fresnel-Kirchhoff integral calculated
by using the stationary phase method, or to the eikonal. Within the paraxial
approximation, we also introduce the ABCD matrices formalism and the beam
quality factor. As an example, we apply these tools to analyse the recent
experiment by Riou et al. [Phys. Rev. Lett. 96, 070404 (2006)].
\\ ( http://arxiv.org/abs/0802.4039 , 408kb)
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arXiv:0802.3972
Date: Wed, 27 Feb 2008 08:46:57 GMT (195kb)

Title: Exotic quantum phase transitions in a Bose-Einstein condensate coupled
to an optical cavity
Authors: Gang Chen, Xiaoguang Wang, J.-Q. Liang, and Z. D. Wang
Categories: quant-ph
\\
A new extended Dicke model, which includes atom-atom interactions and a
driving classical laser field, is established for a Bose-Einstein condensate
inside an ultrahigh-finesse optical cavity. A feasible experimental setup with
a strong atom-field coupling is proposed, where most parameters are easily
controllable and thus the predicted second-order superradiant-normal phase
transition may be detected by measuring the ground-state atomic population.
More intriguingly, two novel quantum phase transitions, one is a first-order
normal phase to "Mott" phase and the other corresponds a second-order
superradiant phase to "Mott" phase, are also revealed. In addition, a rich and
exotic phase diagram is presented.
\\ ( http://arxiv.org/abs/0802.3972 , 195kb)
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arXiv:0802.4055
Date: Wed, 27 Feb 2008 17:24:04 GMT (262kb)

Title: Bifurcations, order, and chaos in the Bose-Einstein condensation of
dipolar gases
Authors: Patrick Wagner, Holger Cartarius, Toma\v{z} Fab\v{c}i\v{c}, J\"org
Main, G\"unter Wunner
Categories: quant-ph
\\
Previous investigations of the Bose-Einstein condensation of dipolar gases
have revealed the existence of universal stability thresholds where collapse of
the condensate sets in. We show that these thresholds in fact correspond to
bifurcation points where always two solutions of the Gross-Pitaevskii equation
disappear in a tangent bifurcation, one dynamically stable and the other
unstable. We point out that the thresholds also correspond to "exceptional
points", i.e. branching singularities of the Hamiltonian. We analyze the
dynamics of excited condensate wave functions via Poincare surfaces of section
and find both regular and chaotic motion, corresponding to (quasi-)
periodically oscillating and irregularly fluctuating condensates, respectively.
Stable islands are found to persist up to energies well above the saddle point
of the mean field energy, alongside with collapsing modes.
\\ ( http://arxiv.org/abs/0802.4055 , 262kb)
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arXiv:0802.4097
Date: Wed, 27 Feb 2008 21:55:09 GMT (719kb)

Title: Manifestations of the Roton Mode in Dipolar Bose-Einstein Condensates
Authors: Ryan M. Wilson, Shai Ronen, Han Pu and John L. Bohn
Categories: cond-mat.other
Comments: 4 pages, 2 column format, 3 figures, submitted to PRL
\\
We investigate the structure of trapped Bose-Einstein condensates (BECs) with
long-range anisotropic dipolar interactions. We find that a small perturbation
in the trapping potential can lead to dramatic changes in the condensate's
density profile for sufficiently large dipolar interaction strengths and trap
aspect ratios. By employing perturbation theory, we relate these oscillations
to a previously-identified roton-like'' mode in dipolar BECs. The same
physics is responsible for radial density oscillations in vortex states of
dipolar BECs that have been predicted previously.
\\ ( http://arxiv.org/abs/0802.4097 , 719kb)
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arXiv:0802.4275
Date: Thu, 28 Feb 2008 20:14:13 GMT (322kb)

Title: Bright solitary waves of trapped atomic Bose-Einstein condensates
Authors: N. G. Parker, A. M. Martin, C. S. Adams and S. L. Cornish
Categories: cond-mat.other
Comments: 8 pages, 5 figures (low quality)
\\
Motivated by recent experimental observations, we study theoretically
multiple bright solitary waves of trapped Bose-Einstein condensates. Through
variational and numerical analyses, we determine the threshold for collapse of
these states. Under $\pi$-phase differences between adjacent waves, we show
that the experimental states lie consistently at the threshold for collapse,
where the corresponding in-phase states are highly unstable. Following the
observation of two long-lived solitary waves in a trap, we perform detailed
three-dimensional simulations which confirm that in-phase waves undergo
collapse while a $\pi$-phase difference preserves the long-lived dynamics and
gives excellent quantitative agreement with experiment. Furthermore,
intermediate phase differences lead to the growth of population asymmetries
between the waves, which ultimately triggers collapse.
\\ ( http://arxiv.org/abs/0802.4275 , 322kb)
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arXiv:0802.4276
Date: Thu, 28 Feb 2008 20:14:54 GMT (68kb)

Title: Fermion- and Spin-Counting in Strongly Correlated Systems
Authors: Sibylle Braungardt, Aditi Sen De, Ujjwal Sen, Roy J. Glauber, Maciej
Lewenstein
Categories: quant-ph
Comments: 8 pages, 7 figures, RevTeX4
\\
We apply the atom counting theory to strongly correlated Fermi systems and
spin models, which can be realized with ultracold atoms. The counting
distributions are typically sub-Poissonian and remain smooth at quantum phase
transitions, but their moments exhibit critical behavior, and characterize
quantum statistical properties of the system. Moreover, more detailed
characterizations are obtained with experimentally feasible spatially resolved
counting distributions.
\\ ( http://arxiv.org/abs/0802.4276 , 68kb)
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\\
arXiv:0802.4098 (*cross-listing*)
Date: Thu, 28 Feb 2008 19:12:44 GMT (822kb)

Title: General Relativistic Effects in Atom Interferometry
Authors: Savas Dimopoulos, Peter W. Graham, Jason M. Hogan, Mark A. Kasevich
Categories: hep-ph gr-qc hep-th physics.atom-ph
\\
Atom interferometry is now reaching sufficient precision to motivate
laboratory tests of general relativity. We begin by explaining the
non-relativistic calculation of the phase shift in an atom interferometer and
deriving its range of validity. From this we develop a method for calculating
the phase shift in general relativity. This formalism is then used to find the
relativistic effects in an atom interferometer in a weak gravitational field
for application to laboratory tests of general relativity. The potentially
testable relativistic effects include the non-linear three-graviton coupling,
the gravity of kinetic energy, and the falling of light. We propose
experiments, one currently under construction, that could provide a test of the
principle of equivalence to 1 part in 1015 (300 times better than the present
limit), and general relativity at the 10% level, with many potential future
improvements. We also consider applications to other metrics including the
Lense-Thirring effect, the expansion of the universe, and preferred frame and
location effects.
\\ ( http://arxiv.org/abs/0802.4098 , 822kb)
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The replacements:

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\\
arXiv:0711.3425
replaced with revised version Tue, 26 Feb 2008 13:13:08 GMT (15kb)

Title: Achieving the Neel state in an optical lattice
Authors: Arnaud Koetsier, R. A. Duine, Immanuel Bloch, H. T. C. Stoof
Categories: cond-mat.stat-mech
Comments: 4 pages, 2 figures, RevTeX. Revised version incorporates minor
Report-no: ITP-UU-07/67
Journal-ref: Phys. Rev. A 77, 023623 (2008)
DOI: 10.1103/PhysRevA.77.023623
\\ ( http://arxiv.org/abs/0711.3425 , 15kb)
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\\
arXiv:0711.1562
replaced with revised version Thu, 28 Feb 2008 00:06:17 GMT (48kb)

Title: Universal Fermi Gas with Two- and Three-Body Resonances
Authors: Yusuke Nishida, Dam Thanh Son, and Shina Tan
Categories: cond-mat.other nucl-th
Comments: 4 pages, 1 figure. Possible experimental realization with cold atoms
in optical lattices is discussed in the 2nd version
\\ ( http://arxiv.org/abs/0711.1562 , 48kb)
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Till next time,
Matt.

--
=========================================================================
Dr M. J. Davis,               Senior Lecturer in Physics
School of Physical Sciences,  email: mdavis_at_physics.uq.edu.au
University of Queensland,     ph   : +61 7 334 69824
Brisbane, QLD 4072,           fax  : +61 7 336 51242
Australia.                    http://www.physics.uq.edu.au/people/mdavis/
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Matt's arXiv selection: weekly summary of cold-atom papers from arXiv.org
http://www.physics.uq.edu.au/people/mdavis/matts_arXiv/
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Received on Mon Mar 03 2008 - 13:49:11 EST

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