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

Date: Mon, 03 Mar 2008 13:49:02 +1000

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

Comments: 4 pages 4 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 6 pages, 5 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 6 pages, 7 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

Comments: 5 pages, 3 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

Comments: 4 pages

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

Comments: 40 pages, 6 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 7 pages, 1 figure

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

Comments: 44pages, 22 figures

License: http://creativecommons.org/licenses/by/3.0/

\\

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

Comments: 2 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

Comments: 16 pages, 19 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 17 pages, 1 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 4 pages, 2 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 10 pages, 9 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 4 pages, 4 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 4 pages, 4 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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)

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

Comments: 34 pages, 7 figures

License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/

\\

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

corrections. Journal reference added

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/ ========================================================================= 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 Mon Mar 03 2008 - 13:49:11 EST

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