From: Matthew Davis <mdavis_at_physics.uq.edu.au>

Date: Fri, 29 May 2009 08:09:52 +1000

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

Comments: RevTeX4, 9 pages

\\

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

Comments: 8 pages, 7 figures

\\

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

Comments: 4 pages, 3 figures

\\

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

Comments: 23 pages, 10 figures

\\

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

Comments: 4 pages, 3 figures

\\

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

Comments: 16 pages, 10 figures

\\

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

Comments: 11 pages, no figure

\\

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

Comments: 10 pages

\\

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

Comments: 5 pages, 4 figures

\\ ( 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/ ========================================================================= Matt's arXiv selection: weekly summary of cold-atom papers from arXiv.org http://www.physics.uq.edu.au/people/mdavis/matts_arXiv/ ========================================================================= Legal stuff: Unless stated otherwise, this e-mail represents only the views of the sender and not the views of the University of Queensland =========================================================================Received on Fri May 29 2009 - 09:12:05 EST

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