# Matt's arXiv selection: week ending 17 April 2009

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Fri, 29 May 2009 08:09:52 +1000

The following message was sent to the matts_arxiv list by Matthew Davis <mdavis_at_physics.uq.edu.au>

Thanks to Jacopo Sabbatini for collating the abstracts for this email. It was a
quiet week with 12 new preprints and 6 replacements.

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arXiv:0904.1723
Date: Fri, 10 Apr 2009 18:01:39 GMT (783kb,D)

Title: Two-point correlation function of a one-dimensional Bose gas in free
expansion
Authors: I. E. Mazets, T. Schumm, and J. Schmiedmayer
Categories: cond-mat.quant-gas
Comments: revtex 4, 4 pages, 3 figures (PDF)
\\
We theoretically investigate the evolution of the two-point correlation
function of an ultra cold gas of bosonic atoms after the release from a tight
waveguide. The correlation function rapidly attains the values characteristic
for a non-degenerate gas: it reaches 2 for vanishing interparticle distance,
and is 1 for distances much larger than the typical correlation length $\lambda _c$. The associated timescale is on the order of $m\lambda_c^2/\hbar$. In the
strongly interacting gas regime $\lambda_c$ is the mean interatomic distance,
in the opposite (weakly interacting) limit it is determined by both the mean
interparticle distance and the temperature of the gas. In the latter limit, the
correlation function, which is initially very close to 1 everywhere, locally
(at distances of about the correlation length) decreases to values
significantly below 1 in the course of evolution.
\\ ( http://arxiv.org/abs/0904.1723 , 783kb)
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arXiv:0904.1750
Date: Fri, 10 Apr 2009 20:15:26 GMT (17kb)

Title: The Yrast Line of a Rapidly Rotating Bose Gas: Gross-Pitaevskii Regime
Authors: Elliott H. Lieb, Robert Seiringer, Jakob Yngvason
Categories: cond-mat.quant-gas
\\
We consider an ultracold rotating Bose gas in a harmonic trap close to the
critical angular velocity so that the system can be considered to be confined
to the lowest Landau level. With this assumption we prove that the
Gross-Pitaevskii energy functional accurately describes the ground state energy
of the corresponding $N$-body Hamiltonian with contact interaction provided the
total angular momentum $L$ is much less than $N^2$. In particular, we validate
the standard belief that the yrast energy is proportional to $N(N-L/2)$ when
$L\leq N$. While the Gross-Pitaevskii energy is always an obvious variational
upper bound to the ground state energy, a more refined analysis is needed to
establish it as an exact lower bound. We also discuss the question of
Bose-Einstein condensation in the parameter range considered. Coherent states
together with inequalities in spaces of analytic functions are the main
technical tools.
\\ ( http://arxiv.org/abs/0904.1750 , 17kb)
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arXiv:0904.2062
Date: Tue, 14 Apr 2009 08:54:23 GMT (2597kb)

Title: Spatially Inhomogeneous Phase Evolution of a Two-Component Bose-Einstein
Condensate
Authors: R. P. Anderson, C. Ticknor, A. I. Sidorov, B. V. Hall
Categories: cond-mat.quant-gas cond-mat.other
\\
We investigate the spatial evolution of the relative phase of an elongated
two-component Bose-Einstein condensate. The pseudo-spin-1/2 system is comprised
of the |F=1,m_F=-1> and |F=2,m_F=+1> hyperfine ground states of 87Rb, which we
magnetically trap and interrogate with radio-frequency and microwave fields. By
performing Ramsey interferometry with the BEC we probe the relative phase
evolution, and observe temporal decay of the interferometric contrast which is
well described by a mean-field formalism. We show that this decay is due to
inhomogeneous growth of the collective relative phase, where decoherence and
phase diffusion are not dominant mechanisms in the loss of interferometric
contrast. We demonstrate a technique that enables simultaneous imaging of each
state, yielding sub percent variations in the measured relative number without
corrupting the spatial mode of each component. In addition we propose a
spatially sensitive interferometric technique to image the relative phase.
\\ ( http://arxiv.org/abs/0904.2062 , 2597kb)
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arXiv:0904.2121
Date: Tue, 14 Apr 2009 13:36:58 GMT (457kb)

Title: Rapid phase-diffusion between atomic and molecular Bose-Einstein
condensates
Authors: I. Tikhonenkov and A. Vardi
Categories: cond-mat.quant-gas
\\
We study the collisional loss of atom-molecule coherence after coherently
dissociating a small fraction of a molecular Bose-Einstein condensate into
atoms. The obtained $n$-atoms states are two-atom (SU(1,1)) coherent states
with number variance $\Delta n\propto n$ compared to $\Delta n\propto \sqrt{n}$
for the spin (SU(2)) coherent states formed by coherent splitting of an atomic
condensate. Consequently, the Lorentzian atom-molecule phase-diffusion is
faster than the Gaussian phase-diffusion between separated atomic condensates,
by a $\sqrt{n}$ factor.
\\ ( http://arxiv.org/abs/0904.2121 , 457kb)
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arXiv:0904.2339
Date: Wed, 15 Apr 2009 16:25:30 GMT (2819kb,D)

Title: Spontaneous pattern formation in an anti-ferromagnetic quantum gas
Authors: Jochen Kronj\"ager, Christoph Becker, Parvis Soltan-Panahi, Kai Bongs,
Klaus Sengstock
Categories: cond-mat.quant-gas
\\
Spontaneous pattern formation is a phenomenon ubiquitous in nature, examples
ranging from Rayleigh-Benard convection to the emergence of complex organisms
from a single cell. In physical systems, pattern formation is generally
associated with the spontaneous breaking of translation symmetry and is closely
related to other symmetry-breaking phenomena, of which (anti-)ferromagnetism is
a prominent example. Indeed, magnetic pattern formation has been studied
extensively in both solid-state materials and classical liquids. Here, we
report on the spontaneous formation of wave-like magnetic patterns in a spinor
Bose-Einstein condensate, extending those studies into the domain of quantum
gases. We observe characteristic modes across a broad range of the magnetic
field acting as a control parameter. Our measurements link pattern formation in
these quantum systems to specific unstable modes obtainable from linear
stability analysis. These investigations open new prospects for controlled
studies of symmetry breaking and the appearance of structures in the quantum
domain.
\\ ( http://arxiv.org/abs/0904.2339 , 2819kb)
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arXiv:0904.2399
Date: Wed, 15 Apr 2009 20:55:00 GMT (111kb)

Title: Bose-Einstein and Fermi-Dirac distributions in nonextensive quantum
statistics: An exact approach
Authors: Hideo Hasegawa (Tokyo Gakugei Univ.)
Categories: cond-mat.stat-mech cond-mat.other
\\
Bose-Einstein (BE) and Fermi-Dirac (FD) distributions in nonextensive quantum
statistics have been discussed with the use of exact integral representations
for the grand canonical partition function [Rajagopal, Mendes and Lenzi, Phys.
Rev. Lett. {\bf 80}, 3907 (1998)]. Integrations along real axis in the case of
$q > 1.0$ are modified by an appropriate change of variable, which makes
numerical calculations feasible, $q$ denoting the entropic index. The $q$
dependence of coefficients in the generalized Sommerfeld expansion has been
calculated. Model calculations have been made with a uniform density of states
for electrons and with the Debye model for phonons. It has been shown that the
linear-$T$ electronic specific heat and the $T^3$ phonon specific heat at low
temperatures are much increased with increasing $q$ from $q=1.0$ while they are
decreased with decreasing $q$ from unity. It is pointed out that the
factorization approximation, which has been applied to many subjects in the
nonextensive quantum systems, is not accurate, and it yields inappropriate
results for $q < 1.0$. Based on the exact results, we propose the approximate
BE and FD distributions, which have the interpolation character yielding
results in agreement with the exact ones in the limits of $q \to 1.0$, zero and
high temperatures.
\\ ( http://arxiv.org/abs/0904.2399 , 111kb)
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arXiv:0904.2564
Date: Thu, 16 Apr 2009 19:29:06 GMT (563kb)

Title: Emergence of turbulence in an oscillating Bose-Einstein condensate
Authors: E.A.L. Henn, J.A.Seman, G.Roati, K.M.F. Magalhaes and V.S. Bagnato
Categories: cond-mat.quant-gas cond-mat.mes-hall
\\
We report on the experimental observation of vortices tangle in an atomic BEC
of Rb-87 atoms when an external oscillatory perturbation is introduced in the
trap. The vortices tangle configuration is a signature of the presence of a
turbulent regime in the cloud. We also show that this turbulent cloud has
suppression of the aspect ratio inversion typically observed in quantum
degenerate bosonic gases during free expansion. Instead, the cloud expands
keeping the ratio between their axis constant. Turbulence in atomic superfluids
may constitute an alternative system to investigate decay mechanisms as well as
to test fundamental theoretical aspects in this field.
\\ ( http://arxiv.org/abs/0904.2564 , 563kb)
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arXiv:0904.2504
Date: Thu, 16 Apr 2009 14:46:34 GMT (2863kb)

Title: Exact theoretical description of two ultracold atoms in a single site of
a 3D optical lattice using realistic interatomic interaction potentials
Authors: Sergey Grishkevich and Alejandro Saenz
Categories: quant-ph cond-mat.quant-gas
\\
A theoretical approach was developed that allows for a full numerical
description of a pair of ultracold atoms trapped in a three-dimensional optical
lattice. This approach includes the possible coupling between center-of-mass
and relative motion coordinates in a configuration-interaction type manner
(also known as exact diagonalization). The atoms are allowed to interact by
their full interaction potential that is presently only limited to be central
and usually only known numerically. With the aid of this approach deviations
from the harmonic approximation are discussed for several heteronuclear atom
pairs that are trapped in a single site of an optical lattice.
\\ ( http://arxiv.org/abs/0904.2504 , 2863kb)
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arXiv:0904.1718
Date: Fri, 10 Apr 2009 17:49:47 GMT (41kb,D)

Title: Restoring integrability in one-dimensional quantum gases by two-particle
correlations
Authors: I. E. Mazets and J. Schmiedmayer
Categories: quant-ph
Comments: revtex4, 4 pages, 1 figure (PDF)
\\
We show that thermalization and the breakdown of integrability in the one
dimensional Lieb-Liniger model caused by local three-body elastic interactions
is suppressed by pairwise quantum correlations when approaching the strongly
correlated regime. If the relative momentum $k$ is small compared to the
two-body coupling constant $c$ the three-particle scattering state is
suppressed by a factor of $(k/c)^{12}$. This demonstrates that in one
dimensional quantum systems it is not the freeze-out of two body collisions but
the strong quantum correlations which ensures integrability.
\\ ( http://arxiv.org/abs/0904.1718 , 41kb)
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arXiv:0904.1774
Date: Sat, 11 Apr 2009 03:00:57 GMT (10kb)

Title: Berry's phase in the two-level model
Authors: A.C. Aguiar Pinto, M. Moutinho and M.T. Thomaz
Categories: quant-ph
\\
We study the adiabatic evolution of a two-level model in the presence of an
external classical electric field. The coupling between the quantum model and
the classical field is taken in the electric dipole approximation. In this
regime, we show the absence of geometric phases in the interacting two-level
model in the presence of any periodic real time-dependent classical electric
field. We obtain a conservative scalar potential in the calculation of Berry's
phases of the instantaneous eigenstates of the model. For complex electric
fields, we recover the existence of geometric phases. In particular, the
geometric phases of the instantaneous eigenstates of the model in the presence
of a positive or of a negative frequency component of the monochromatic
electric field differ by an overall sign. As a check on our results, we map
this interacting two-level model onto a spin-1/2 model under the action of a
classical magnetic field. We confirm that the first one acquires Berry's phase
only in the rotating wave approximation [RWA].
\\ ( http://arxiv.org/abs/0904.1774 , 10kb)
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arXiv:0904.2126
Date: Tue, 14 Apr 2009 14:11:48 GMT (6kb)

Title: Critical exponents for Gaussian fixed point of renormalization
Authors: Witold Haliniak and Wojciech Wislicki
Categories: cond-mat.stat-mech
\\
We present mathematical details of derivation of the critical exponents for
the free energy and magnetization in the vicinity of the Gaussian fixed point
of renormalization. We treat the problem in general terms and do not refer to
particular models of interaction energy. We discuss the case of arbitrary
dispersion of the fixed point.
\\ ( http://arxiv.org/abs/0904.2126 , 6kb)
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arXiv:0904.2241
Date: Wed, 15 Apr 2009 05:53:57 GMT (16kb)

Title: Time-dependent Nonequilibrium Thermodynamics: A Master-equation Approach
Authors: Hao Ge
Categories: cond-mat.stat-mech
\\
Master equation could be applied to model various kinds of biochemical
systems. A general theory for its time-dependent nonequilibrium thermodynamics
is rigorously derived. We not only introduce a concept of general internal
energy, but also propose an extension of the equilibrium state. Moreover, we
find out an explicit expression for the extended form of the Second Law, which
is phenomenologically stated as "the conversion of work to excess heat is
irreversible". The theory is carefully applied to several thermodynamic
processes, and its consistence with the classical thermodynamics is clearly
shown.
\\ ( http://arxiv.org/abs/0904.2241 , 16kb)
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The replacments:

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arXiv:0904.1727
replaced with revised version Mon, 13 Apr 2009 22:56:54 GMT (962kb)

Title: Pauli blocking of light scattering in a trapped Fermi gas
Authors: B. Shuve and J. H. Thywissen
Categories: cond-mat.quant-gas cond-mat.stat-mech
Comments: 9 pages, 8 figures. v2: minor corrections to references and figures
\\ ( http://arxiv.org/abs/0904.1727 , 962kb)
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arXiv:0812.1204
replaced with revised version Tue, 14 Apr 2009 13:46:50 GMT (660kb)

Title: Phase-diffusion dynamics in weakly coupled Bose-Einstein condensates
Authors: Erez Boukobza, Maya Chuchem, Doron Cohen, and Amichay Vardi
Categories: cond-mat.other
\\ ( http://arxiv.org/abs/0812.1204 , 660kb)
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arXiv:cond-mat/0603842
replaced with revised version Wed, 15 Apr 2009 13:16:10 GMT (264kb)

Title: Density Matrix Renormalization Group for Dummies
Authors: G. De Chiara, M. Rizzi, D. Rossini and S. Montangero
Categories: cond-mat.other quant-ph
Comments: 29 pages, 9 figures. Published version. An open source version of the
code can be found at http://qti.sns.it/dmrg/phome.html
Journal-ref: J. Comput. Theor. Nanosci. 5, 1277-1288 (2008)
DOI: 10.1166/jctn.2008.011
\\ ( http://arxiv.org/abs/cond-mat/0603842 , 264kb)
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arXiv:0806.1517
replaced with revised version Tue, 14 Apr 2009 20:24:14 GMT (103kb)

Title: Stirring trapped atoms into fractional quantum Hall puddles
Authors: Stefan K. Baur, Kaden R. A. Hazzard, and Erich J. Mueller (Cornell)
Categories: cond-mat.quant-gas cond-mat.mes-hall cond-mat.other
Comments: 4 pages, 3 figures (13 subfigures) -- v2: published version
Journal-ref: Phys. Ref. A 78, 061608 (2008)
DOI: 10.1103/PhysRevA.78.061608
\\ ( http://arxiv.org/abs/0806.1517 , 103kb)
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arXiv:0809.4189
replaced with revised version Wed, 15 Apr 2009 15:32:25 GMT (29kb)

Title: A strongly interacting Bose gas: Nozi\eres and Schmitt-Rink theory and
beyond
Authors: Arnaud Koetsier, P. Massignan, R. A. Duine and H. T. C. Stoof
Categories: cond-mat.other
Comments: 8 pages, 8 figures, RevTeX. Significantly expanded to include effects
beyond NSR
Report-no: ITP-UU-08/56
\\ ( http://arxiv.org/abs/0809.4189 , 29kb)
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arXiv:0709.3381
Date: Fri, 21 Sep 2007 12:26:12 GMT (34kb,D)
Date (revised v2): Wed, 28 Nov 2007 15:22:32 GMT (40kb,D)
Date (revised v3): Sat, 2 Aug 2008 15:50:06 GMT (134kb)
Date (revised v4): Wed, 15 Apr 2009 17:02:51 GMT (318kb)

Title: Generalized ABCD propagation for interacting atomic clouds
Authors: F. Impens and Ch. J. Bord\'e
Categories: cond-mat.quant-gas cond-mat.other physics.atom-ph physics.optics
quant-ph
Comments: 15 pages, 4 figures, Final version
Journal-ref: Phys. Rev. A 79, 043613 (2009)
\\ ( http://arxiv.org/abs/0709.3381 , 318kb)
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Till next time,
Matt.

--
=========================================================================
Dr M. J. Davis,                      Associate Professor in Physics
School of Mathematics and Physics,   ph  : +61 7 334 69824
The University of Queensland,        fax : +61 7 336 51242
Brisbane, QLD 4072,                  mdavis_at_physics.uq.edu.au
Australia.                           www.physics.uq.edu.au/people/mdavis/
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http://www.physics.uq.edu.au/people/mdavis/matts_arXiv/
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Received on Fri May 29 2009 - 09:12:05 EST

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