Matt's arXiv selection, Tuesday 12th September 2006.

From: Matthew Davis <>
Date: Tue, 12 Sep 2006 13:35:41 +1000 (EST)

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Abstracts for this week:

Paper: cond-mat/0609007
Date: Fri, 1 Sep 2006 01:54:29 GMT (977kb)

Title: Coherence-enhanced imaging of a degenerate Bose gas
Authors: L. E. Sadler, J. M. Higbie, S. R. Leslie, M. Vengalattore, and D. M.
Comments: 4 pages, 4 figures
Subj-class: Other
   We present coherence-enhanced imaging, an in situ technique that uses Raman
superradiance to probe the spatial coherence properties of an ultracold gas.
Applying this method, we obtain a spatially resolved measurement of the
condensate number and more generally, of the first-order spatial correlation
function in a gas of $^{87}$Rb atoms. We observe the enhanced decay of
propagating spin gratings in high density regions of a Bose condensate, a decay
we ascribe to collective, non-linear atom-atom scattering. Further, we directly
observe spatial inhomogeneities that arise generally in the course of extended
sample superradiance.
\\ ( , 977kb)
Paper: cond-mat/0609014
Date: Fri, 1 Sep 2006 09:18:48 GMT (317kb)

Title: Condensate splitting in an asymmetric double well for atom chip based
Authors: B.V.Hall, S.Whitlock, R.Anderson, P.Hannaford and A.Sidorov
Comments: 4 pages, 5 figures
Subj-class: Other
   We report on the adiabatic splitting of a BEC of $^{87}$Rb atoms by an
asymmetric double-well potential located above the edge of a perpendicularly
magnetized TbGdFeCo film atom chip. By controlling the barrier height and
double-well asymmetry the sensitivity of the axial splitting process is
investigated through observation of the fractional atom distribution between
the left and right wells. This process constitutes a novel sensor for which we
infer a single shot sensitivity to gravity fields of $\delta
g/g\approx2\times10^{-4}$. From a simple analytic model we propose improvements
to chip-based gravity detectors using this demonstrated methodology.
\\ ( , 317kb)
Paper (*cross-listing*): math-ph/0608069
Date: Thu, 31 Aug 2006 15:29:54 GMT (39kb)

Title: Free Energy of a Dilute Bose Gas: Lower Bound
Authors: Robert Seiringer
Comments: LaTeX2e, 53 pages
Subj-class: Mathematical Physics; Statistical Mechanics
   A lower bound is derived on the free energy (per unit volume) of a
homogeneous Bose gas at density $\rho$ and temperature $T$. In the dilute
regime, i.e., when $a^3\rho \ll 1$, where $a$ denotes the scattering length of
the pair-interaction potential, our bound differs to leading order from the
expression for non-interacting particles by the term $4\pi a (2\rho^2 -
[\rho-\rho_c]_+^2)$. Here, $\rho_c(T)$ denotes the critical density for
Bose-Einstein condensation (for the non-interacting gas), and $[ ]_+$ denotes
the positive part. Our bound is uniform in the temperature up to temperatures
of the order of the critical temperature, i.e., $T \sim \rho^{2/3}$ or smaller.
One of the key ingredients in the proof is the use of coherent states to extend
the method introduced in [arXiv:math-ph/0601051] for estimating correlations to
temperatures below the critical one.
\\ ( , 39kb)
Paper: cond-mat/0604184
replaced with revised version Thu, 31 Aug 2006 22:42:48 GMT (29kb)

Title: Two-species fermion mixtures with population imbalance
Authors: M. Iskin and C. A. R. Sa de Melo
Comments: 4 pages with 3 figures, accepted version to PRL
Subj-class: Superconductivity; Other
\\ ( , 29kb)
Paper: cond-mat/0608721
replaced with revised version Fri, 1 Sep 2006 15:56:39 GMT (135kb)

Title: Repulsively bound atom pairs: Overview, Simulations and Links
Authors: A. J. Daley, A. Kantian, H. P. B\"uchler, P. Zoller, K. Winkler, G.
   Thalhammer, F. Lang, R. Grimm, J. Hecker Denschlag
Comments: 7 pages, 3 figures, Proceedings of ICAP-2006 (Innsbruck)
Subj-class: Other
\\ ( , 135kb)
Paper: quant-ph/0609003
Date: Fri, 1 Sep 2006 08:09:33 GMT (870kb)

Title: Influence of classical resonances on chaotic tunnelling
Authors: Amaury Mouchet (LMPT), Christopher Eltschka, Peter Schlagheck
Proxy: ccsd ccsd-00090587
Journal-ref: Physical Review E 74 (2006) 026211
DOI: 10.1103/PhysRevE.74.026211
   Dynamical tunnelling between symmetry-related stable modes is studied in the
periodically driven pendulum. We present strong evidence that the tunnelling
process is governed by nonlinear resonances that manifest within the regular
phase-space islands on which the stable modes are localized. By means of a
quantitative numerical study of the corresponding Floquet problem, we identify
the trace of such resonances not only in the level splittings between
near-degenerate quantum states, where they lead to prominent plateau
structures, but also in overlap matrix elements of the Floquet eigenstates,
which reveal characteristic sequences of avoided crossings in the Floquet
spectrum. The semiclassical theory of resonance-assisted tunnelling yields good
overall agreement with the quantum-tunnelling rates, and indicates that partial
barriers within the chaos might play a prominent role.
\\ ( , 870kb)
Paper: cond-mat/0609036
Date: Sat, 2 Sep 2006 07:00:33 GMT (114kb)

Title: Screening effect and delocalization of interacting Bose-Einstein
   condensates in random potentials
Authors: Laurent Sanchez-Palencia (LCFIO)
Proxy: ccsd ccsd-00090760
Subj-class: Other
   We theoretically investigate the physics of interacting Bose-Einstein
condensates at equilibrium in a weak (possibly random) potential. We develop a
perturbation approach to derive the condensate wavefunction for an amplitude of
the potential smaller than the chemical potential of the condensate and for an
arbitrary spatial variation scale of the potential. Applying this theory to
disordered potentials, we find in particular that, if the healing length is
smaller than the latter, the condensate assumes a delocalized Thomas-Fermi
profile. In the opposite situation where the typical variation scale of the
potential is smaller than the healing length, we show that the random potential
can be significantly screened and, in the meanfield regime, the condensate
wavefunction can remain delocalized, even for very small correlation lengths of
the disorder.
\\ ( , 114kb)
Paper: cond-mat/0609047
Date: Sun, 3 Sep 2006 11:59:52 GMT (74kb)

Title: Intrinsic dephasing in one dimensional ultracold atom interferometers
Authors: Rafi Bistritzer and Ehud Altman (Weizmann)
Subj-class: Other; Mesoscopic Systems and Quantum Hall Effect
   Quantum phase fluctuations play a crucial role in low dimensional systems. In
particular they prevent true long range phase order from forming in one
dimensional condensates, even at zero temperature. Nevertheless, by dynamically
splitting the condensate into two parallel decoupled tubes, a macroscopic
relative phase, can be imposed on the system. This kind of setup can serve as a
matter wave interferometer, which relies on the interference between the
displaced condensates as a measure of the relative phase between them. Here we
show how the quantum phase fluctuations, which are so effective in equilibrium,
act to destroy the macroscopic relative phase that was imposed as a non
equilibrium initial condition of the interferometer. We show that the phase
coherence between the two condensates decays exponentially with a dephasing
time that depends on intrinsic parameters: the dimensionless interaction
strength, sound velocity and density. Interestingly, at low temperatures the
dephasing time is almost independent of temperature. At temperatures higher
than a crossover scale T* dephasing gains significant temperature dependance.
In contrast to the usual phase diffusion, which is essentially an effect of
confinement, the dephasing due to fluctuations in one dimension is a bulk
effect that survives the thermodynamic limit.
\\ ( , 74kb)
Paper: cond-mat/0609052
Date: Mon, 4 Sep 2006 07:28:03 GMT (21kb)

Title: Quantum Field Theoretical Description of Unstable Behavior of
   Bose-Einstein Condensates in a Trapping Potential with Complex Eigenvalues of
   Bogoliubov-de Gennes Equations
Authors: M. Mine, M. Okumura, T. Sunaga, Y. Yamanaka
Comments: 30 pages
Subj-class: Other
   The Bogoliubov-de Gennes equations are used for a number of theoretical works
on the trapped Bose-Einstein condensates. These equations are known to give the
energies of the quasi-particles when all the eigenvalues are real. We consider
the case in which these equations have complex eigenvalues. We give the
complete set including those modes whose eigenvalues are complex. The quantum
fields which represent neutral atoms are expanded in terms of the complete set.
It is shown that the state space is an indefinite metric one and that the free
Hamiltonian is not diagonalizable in the conventional bosonic representation.
We introduce a criterion to select quantum states describing the metastablity
of the condensate, called the physical state conditions. In order to study the
instability, we formulate the linear response of the density against the
time-dependent external perturbation within the regime of Kubo's linear
response theory. Some states, satisfying all the physical state conditions,
give the blow-up and damping behavior of the density distributions
corresponding to the complex eigenmodes. It is consistent with the result of
the recent analyses using the time-dependent Gross-Pitaevskii equation.
\\ ( , 21kb)
Paper: cond-mat/0609061
Date: Mon, 4 Sep 2006 10:21:26 GMT (467kb)

Title: Einstein-de Haas effect for a $^{87}$Rb atoms condensate
Authors: Krzysztof Gawryluk, Miros{\l}aw Brewczyk, Kai Bongs, and Mariusz Gajda
Comments: 4 pages, 5 figures
Subj-class: Other
   We consider a condensate of $^{87}$Rb atoms in an F=1 hyperfine state
confined in an optical dipole trap. Assuming the magnetic moments of all atoms
are initially aligned along the magnetic field we observe, after the field's
direction is reversed, a transfer of atoms to other Zeeman states due to the
dipolar interaction. We find that there exist resonances which amplify the
effect of dipolar interaction. When the resonance condition is satisfied the
transfer of atoms to $m_F=0,-1$ states might be of the order of the initial
population of $m_F=1$ component. While changing the magnetic moments during the
transfer, the atomsacquire an orbital angular momentum and start to circulate
around the center of the trap. This is a realization of the famous Einstein-de
Haas effect in systems of cold gases. Due to the dipolar resonances, it becomes
possible to observe this phenomenon even in a condensate of $^{87}$Rb (F=1)
atoms that have very small magnetic moment.
\\ ( , 467kb)
Paper: cond-mat/0609063
Date: Mon, 4 Sep 2006 12:56:09 GMT (238kb)

Title: Stochastic mean-field approach to strongly correlated phases of
   ultracold fermions
Authors: Olivier Juillet (LPCC)
Comments: Submitted to Physical Review Letters
Proxy: ccsd ccsd-00090944
Subj-class: Other
   We propose a new projector quantum Monte-Carlo method to investigate the
ground state of ultracold fermionic atoms modeled by a lattice Hamiltonian with
an on-site interaction. The many-body state is reconstructed from Slater
determinants that evolve in imaginary-time according to a stochastic mean-field
motion without explicit sign problems. The method is applied to calculate
ground-state energies and correlation functions of the repulsive
two-dimensional Hubbard model. Numerical results for the unitary Fermi gas
validate simulations with nodal constraints.
\\ ( , 238kb)
Paper: cond-mat/0609067
Date: Mon, 4 Sep 2006 14:29:55 GMT (21kb)

Title: Mean-Field vs Monte-Carlo equation of state for the expansion of a Fermi
   superfluid in the BCS-BEC crossover
Authors: Luca Salasnich (CNISM and CNR-INFM, Padova) and Nicola Manini (Univ.
Comments: 13 pages, 3 figures, presented to the 15th International Laser
   Physics Workshop (Lausanne, July 24-28, 2006); to be published in Laser
Subj-class: Other
   The equation of state (EOS) of a Fermi superfluid is investigated in the
BCS-BEC crossover at zero temperature. We discuss the EOS based on Monte-Carlo
(MC) data and asymptotic expansions and the EOS derived from the extended BCS
(EBCS) mean-field theory. Then we introduce a time-dependent density
functional, based on the bulk EOS and Landau's superfluid hydrodynamics with a
von Weizs\"acker-type correction, to study the free expansion of the Fermi
superfluid. We calculate the aspect ratio and the released energy of the
expanding Fermi cloud showing that MC EOS and EBCS EOS are both compatible with
the available experimental data of $^6$Li atoms. We find that the released
energy satisfies an approximate analytical formula that is quite accurate in
the BEC regime. For an anisotropic droplet, our numerical simulations show an
initially faster reversal of anisotropy in the BCS regime, later suppressed by
the BEC fluid.
\\ ( , 21kb)
Paper: physics/0605225
replaced with revised version Sat, 2 Sep 2006 07:52:34 GMT (70kb)

Title: Worm Algorithm and Diagrammatic Monte Carlo: A New Approach to
   Continuous-Space Path Integral Monte Carlo Simulations
Authors: M. Boninsegni, N. V. Prokof'ev and B. V. Svistunov
Comments: 17 pages, 13 figures
Subj-class: Computational Physics; Statistical Mechanics
Journal-ref: Phys. Rev. E 74, 036701 (2006)
\\ ( , 70kb)
Paper: quant-ph/0609009
Date: Sat, 2 Sep 2006 01:59:50 GMT (182kb)

Title: Extended Coherence Time with Atom-Number Squeezed Sources
Authors: Wei Li, Ari K. Tuchman, Hui-Chun Chien, Mark A. Kasevich
Comments: 4 pages, 4 figures
   Coherence properties of Bose-Einstein condensates offer the potential for
improved interferometric phase contrast. However, decoherence effects due to
the mean-field interaction shorten the coherence time, thus limiting potential
sensitivity. In this work, we demonstrate increased coherence times with number
squeezed states in an optical lattice using the decay of Bloch oscillations to
probe the coherence time. We extend coherence times by a factor of 2 over those
expected with coherent state BEC interferometry. We observe quantitative
agreement with theory both for the degree of initial number squeezing as well
as for prolonged coherence times.
\\ ( , 182kb)
Paper: quant-ph/0609019
Date: Mon, 4 Sep 2006 14:25:04 GMT (481kb)

Title: Producing and Detecting Correlated atoms
Authors: Christoph I. Westbrook (LCFIO), Martijn Schellekens (LCFIO),
   Aur\'{e}lien Perrin (LCFIO), Valentina Krachmalnicoff (LCFIO), Jose Carlos
   Viana Gomes (LCFIO, Departamento De Fisica, Universidade Do Minho),
   Jean-Baptiste Trebbia (LCFIO), J\'{e}r\^{o}me Est\`{e}ve (LCFIO), Hong Chang
   (LCFIO), Isabelle Bouchoule (LCFIO), Denis Boiron (LCFIO), Alain Aspect
   (LCFIO), Tom Jeltes (LASER Center Vrije Universiteit Amsterdam), John
   McNamara (LASER Center Vrije Universiteit Amsterdam), Wim Hogervorst (LASER
   Center Vrije Universiteit Amsterdam), Wim Vassen (LASER Center Vrije
   Universiteit Amsterdam)
Comments: to appear in conference proceedings "Atomic Physics 20"
Proxy: ccsd ccsd-00090936
Journal-ref: International Conference on Atomic Physics,, Autriche (2006)
   We discuss experiments to produce and detect atom correlations in a
degenerate or nearly degenerate gas of neutral atoms. First we treat the atomic
analog of the celebrated Hanbury Brown Twiss experiment, in which atom
correlations result simply from interference effects without any atom
interactions.We have performed this experiment for both bosons and fermions.
Next we show how atom interactions produce correlated atoms using the atomic
analog of spontaneous four-wavemixing. Finally, we briefly mention experiments
on a one dimensional gas on an atom chip in which correlation effects due to
both interference and interactions have been observed.
\\ ( , 481kb)
Paper: physics/0609013
Date: Fri, 1 Sep 2006 21:32:23 GMT (180kb)

Title: Simple Theoretical Models for Resonant Cold Atom Interactions
Authors: Paul S. Julienne, Bo Gao
Comments: To be published in the Proceedings of the 20th International
   Conference on Atomic Physics, held in Innsbruck, Austria, July 2006
Subj-class: Atomic Physics
   Magnetically tunable scattering resonances have been used with great success
for precise control of s-wave scattering lengths in ultracold atomic
collisions. We describe relatively simple yet quite powerful analytic
treatments of such resonances based on the analytic properties of the van der
Waals long range potential. This theory can be used to characterize a number of
properties of specific resonances that have been used successfully in various
experiments with $^{87}$Rb, $^{85}$Rb, $^{40}$K, and $^{6}$Li. Optical Feshbach
resonances are also possible and may be practical with narrow intercombination
line photoassociative transitions in species like Sr and Yb.
\\ ( , 180kb)
Paper: physics/0609028
Date: Mon, 4 Sep 2006 07:33:31 GMT (852kb)

Title: Large atom number Bose-Einstein condensate of sodium
Authors: K.M.R. van der Stam, E.D. van Ooijen, R. Meppelink, J.M. Vogels, and
   P. van der Straten
Comments: 11 pages, 12 figures, submitted to Review Of Scientific Instruments
Subj-class: Atomic Physics
   We describe the setup to create a large Bose-Einstein condensate containing
more than 120x10^6 atoms. In the experiment a thermal beam is slowed by a
Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical
dark-spot MOT in our experiments contains 2.0x10^10 atoms with a temperature of
320 microK and a density of about 1.0x10^11 atoms/cm^3. The sample is spin
polarized in a high magnetic field, before the atoms are loaded in the magnetic
trap. Spin polarizing in a high magnetic field results in an increase in the
transfer efficiency by a factor of 2 compared to experiments without spin
polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by
evaporative cooling. To suppress the 3-body losses at the end of the
evaporation the magnetic trap is decompressed in the axial direction.
\\ ( , 852kb)
Paper: cond-mat/0508466
replaced with revised version Tue, 5 Sep 2006 13:30:31 GMT (130kb)

Title: Hanbury Brown Twiss effect for ultracold quantum gases
Authors: M. Schellekens, R. Hoppeler, A. Perrin, J. Viana Gomes, D. Boiron, A.
   Aspect, C. I. Westbrook
Comments: Figure 1 available
Subj-class: Other
Journal-ref: published in Science 310, 648 (2005)
\\ ( , 130kb)
Paper: cond-mat/0603626
replaced with revised version Tue, 5 Sep 2006 17:52:35 GMT (0kb,I)

Title: Non-Positive $\alpha$ Rule for Continuous Phase Transition Lines
Authors: Nikolay Prokof'ev, Boris Svistunov
Comments: This paper has been withdrawn by the authors, due to a possible flaw
   in its logic. Namely, it has been taken for granted that the the structure of
   regular part of Helmholtz free energy is insensitive to the sign of the
   specific heat exponent
Subj-class: Statistical Mechanics
\\ ( , 0kb)
Paper: cond-mat/0605039
replaced with revised version Tue, 5 Sep 2006 09:01:26 GMT (62kb)

Title: Intermediate temperature superfluidity in an atomic Fermi gas with
   population imbalance
Authors: Chih-Chun Chien, Qijin Chen, Yan He, and K. Levin
Comments: Replace with the published version
Subj-class: Strongly Correlated Electrons; Superconductivity
Journal-ref: Phys. Rev. Lett. 97, 090402 (2006)
DOI: 10.1103/PhysRevLett.97.090402
\\ ( , 62kb)
Paper: cond-mat/0606743
replaced with revised version Tue, 5 Sep 2006 01:14:33 GMT (62kb)

Title: Predicted quantum stripe ordering in optical lattices
Authors: Congjun Wu, W. Vincent Liu, Joel Moore, and Sankar Das Sarma
Comments: 5 pages, three figures
Subj-class: Strongly Correlated Electrons; Superconductivity
\\ ( , 62kb)
Paper: cond-mat/0609050
Date: Mon, 4 Sep 2006 02:04:11 GMT (574kb)

Title: Quantum phase transitions of light
Authors: Andrew D. Greentree, Charles Tahan, Jared H. Cole, and L. C. L.
Comments: 11 pages, 5 figures (2 in colour)
Subj-class: Other
   Recently, condensed matter and atomic experiments have reached a length-scale
and temperature regime where new quantum collective phenomena emerge. Finding
such physics in systems of photons, however, is problematic, as photons
typically do not interact with each other and can be created or destroyed at
will. Here, we introduce a physical system of photons that exhibits strongly
correlated dynamics on a meso-scale. By adding photons to a two-dimensional
array of coupled optical cavities each containing a single two-level atom in
the photon-blockade regime, we form dressed states, or polaritons, that are
both long-lived and strongly interacting. Our zero temperature results predict
that this photonic system will undergo a characteristic Mott insulator
(excitations localised on each site) to superfluid (excitations delocalised
across the lattice) quantum phase transition. Each cavity's impressive photon
out-coupling potential may lead to actual devices based on these quantum
many-body effects, as well as observable, tunable quantum simulators. We
explicitly show that such phenomena may be observable in micro-machined diamond
containing nitrogen-vacancy colour centres and superconducting microwave
strip-line resonators.
\\ ( , 574kb)
Paper: physics/0605092
replaced with revised version Tue, 5 Sep 2006 12:01:19 GMT (341kb)

Title: Diffuse reflection of a Bose-Einstein condensate from a rough evanescent
   wave mirror
Authors: Helene Perrin, Yves Colombe, Brigitte Mercier, Vincent Lorent, and
   Carsten Henkel
Comments: submitted to J Phys B, 10 pages, 6 figures
Subj-class: Atomic Physics; Optics
\\ ( , 341kb)
Paper (*cross-listing*): nucl-th/0608063
Date: Mon, 28 Aug 2006 11:10:21 GMT (96kb)
Date (revised v2): Wed, 6 Sep 2006 10:07:25 GMT (96kb)

Title: $D$-dimensions Dirac fermions BEC-BCS cross-over thermodynamics with
   Lorentz violation
Authors: Ji-sheng Chen
Comments: 7 pages, 2 figures; typos fixed
Subj-class: Nuclear Theory; Statistical Mechanics
   An analytical attempt is made with an effective Proca Lagrangian action to
address the vector condensation Lorentz violation effects on the equation of
state of strongly interacting fermions system. The in-medium many-body
renormalization effect is introduced as an external field approximation through
a fictive generalized Thomson Problem background. The expressions for the
$d$-dimensions thermodynamics are given with finite $S$-wave scattering length.
In the non-relativistic limit for $d=3$, universal coefficient $\xi ={4/9}$ and
energy gap $\Delta ={5/18}\epsilon_f $ are reasonably consistent with the
existed theoretical and experimental results. In the unitary limit for $d=2$
and T=0, the universal dimensionless coefficient can even approach the extreme
occasion $\xi=0$ corresponding to $m^*=\infty$ which can be mapped to the
strongly coupled two-dimensions electrons and is quite similar to the
3-dimensions Bose-Einstein Condensation of ideal boson gas. Instead, for $d=1$,
the universal coefficient $\xi$ is negative, implying the non-existence of
phase transition from superfluidity to normal state. The solutions manifest the
quantum Ising characteristic of the strongly coupled unitary fermions gas.
\\ ( , 96kb)
Paper: cond-mat/0605169
replaced with revised version Wed, 6 Sep 2006 07:15:35 GMT (211kb)

Title: Fermion pairing with spin-density imbalance in an optical lattice
Authors: T. Koponen, J. Kinnunen, J.-P. Martikainen, L.M. Jensen, and P. Torma
Comments: 18 pages, 17 figures, replaced with published version, also available
Subj-class: Superconductivity; Materials Science
Journal-ref: New J. Phys. 8 (2006) 179
DOI: 10.1088/1367-2630/8/9/179
\\ ( , 211kb)
Paper: cond-mat/0605148
replaced with revised version Tue, 5 Sep 2006 21:55:43 GMT (9kb)

Title: Bose-Einstein condensation and entanglement in magnetic systems
Authors: Mucio A. Continentino
Comments: 7 pages, 1 Table; accepted version; changes in text and new
Subj-class: Strongly Correlated Electrons; Statistical Mechanics
Journal-ref: J.Phys.: Condens. Matter 18 (2006) 8395-8401
\\ ( , 9kb)
Paper: cond-mat/0608611
replaced with revised version Wed, 6 Sep 2006 19:13:48 GMT (47kb)

Title: Excited state spectra at the superfluid-insulator transition out of
   paired condensates
Authors: Stephen Powell and Subir Sachdev
Comments: 4 pages, 1 figure
Subj-class: Strongly Correlated Electrons; Superconductivity
\\ ( , 47kb)
Paper: physics/0609041
Date: Wed, 6 Sep 2006 00:20:28 GMT (53kb)

Title: Robust, High-speed, All-Optical Atomic Magnetometer
Authors: J. M. Higbie, E. Corsini, and D. Budker
Comments: 8 pages, 5 figs
Subj-class: Atomic Physics; Instrumentation and Detectors
   A self-oscillating magnetometer based on the nonlinear magneto-optical
rotation effect with separate modulated pump and unmodulated probe beams is
demonstrated. This device possesses a bandwidth exceeding $1\khz$. Pump and
probe are delivered by optical fiber, facilitating miniaturization and
modularization. The magnetometer has been operated both with vertical-cavity
surface-emitting lasers (VCSELs), which are well suited to portable
applications, and with conventional edge-emitting diode lasers. A sensitivity
of around $3 {\rm nG}$ is achieved for a measurement time of $1\s$.
\\ ( , 53kb)
Paper: physics/0608088
replaced with revised version Wed, 6 Sep 2006 14:27:22 GMT (361kb)

Title: Evaporative cooling in a radio-frequency trap
Authors: Carlos L. Garrido Alzar (1), H\'el\`ene Perrin (1), Barry M. Garraway
   (2), Vincent Lorent (1) ((1) Laboratoire de Physique des Lasers,
   CNRS-Universit\'e Paris 13, Villetaneuse, France, (2) Department of Physics
   and Astronomy, University of Sussex, Brighton, United Kingdom)
Comments: 12 pages, 11 figures
Subj-class: Atomic Physics
\\ ( , 529kb)
Paper: cond-mat/0609156
Date: Thu, 7 Sep 2006 06:35:29 GMT (8kb)

Title: Local stability conditions for asymmetric Fermi superfluid
Authors: S.-K. Yip
Subj-class: Superconductivity
   Two different local stability conditions for an asymmetric superfluid has
been discussed in the literature. We here consider the relations between them.
\\ ( , 8kb)
Paper: cond-mat/0609159
Date: Thu, 7 Sep 2006 08:09:07 GMT (30kb)

Title: Condensation of phonons in an ultracold Bose gas
Authors: Yu. Kagan and L.A. Manakova
Comments: 5 pages, 1 figure, submitted to Phys.Rev.Letters
Subj-class: Other
   We consider the generation of longitudinal phonons in an elongated
Bose-condensed gas at zero temperature due to parametric resonance as a result
of the modulation of the transverse trap frequency. The nonlinear temporal
evolution with account of the phonon-phonon interaction leads self-consistently
to the formation of the stationary state with the macroscopic occupation of a
single phonon quantum state.
\\ ( , 30kb)
Paper: cond-mat/0609167
Date: Thu, 7 Sep 2006 10:50:05 GMT (38kb)

Title: Thermodynamics of Solitonic Matter Waves in a Toroidal Trap
Authors: L. Salasnich (CNISM and CNR-INFM), A. Parola (Univ. Insubria), and L.
   Reatto (Univ. Milano)
Comments: 4 pages, 4 figures, to be published in Physical Review A as a Rapid
   Communication. Related papers can be found at
Subj-class: Other; Statistical Mechanics
   We investigate the thermodynamic properties of a Bose-Einstein condensate
with negative scattering length confined in a toroidal trapping potential. By
numerically solving the coupled Gross-Pitaevskii and Bogoliubov-de Gennes
equations, we study the phase transition from the uniform state to the
symmetry-breaking state characterized by a bright-soliton condensate and a
localized thermal cloud. In the localized regime three states with a finite
condensate fraction are present: the thermodynamically stable localized state,
a metastable localized state and also a metastable uniform state. Remarkably,
the presence of the stable localized state strongly increases the critical
temperature of Bose-Einstein condensation.
\\ ( , 38kb)
Paper: cond-mat/0609169
Date: Thu, 7 Sep 2006 11:25:58 GMT (123kb)

Title: The new physics of non-equilibrium condensates: insights from classical
Authors: P. R. Eastham
Comments: 10 pages, 4 figures, submitted for a special issue of J. Phys.:
   Condensed Matter on "Optical coherence and collective phenomena in
Subj-class: Strongly Correlated Electrons; Mesoscopic Systems and Quantum Hall
   We discuss the dynamics of classical Dicke-type models, aiming to clarify the
mechanisms by which coherent states could develop in potentially
non-equilibrium systems such as semiconductor microcavities. We present
simulations of an undamped model which show spontaneous coherent states with
persistent oscillations in the magnitude of the order parameter. These states
are generalisations of superradiant ringing to the case of inhomogeneous
broadening. They resemble the persistent gap oscillations proposed in fermionic
atomic condensates, but arise from different initial conditions. We show that
introducing randomness into the couplings can suppress the oscillations,
leading to a limiting dynamics with a time-independent order parameter. This
demonstrates that non-equilibrium generalisations of polariton condensates can
be created even without dissipation. We explain the dynamical origins of the
coherence as instabilities of the normal state, and consider how it can
additionally develop through scattering and dissipation.
\\ ( , 123kb)
Paper: cond-mat/0609171
Date: Thu, 7 Sep 2006 13:16:56 GMT (413kb)

Title: Symmetry Breaking in Bose-Einstein Condensates
Authors: Masahito Ueda, Yuki Kawaguchi, Hiroki Saito, Rina Kanamoto, and
   Tatsuya Nakajima
Comments: Submitted to the proceedings of International Conference on Atomic
   Physics 2006
Subj-class: Other
   A gaseous Bose-Einstein condensate (BEC) offers an ideal testing ground for
studying symmetry breaking, because a trapped BEC system is in a mesoscopic
regime, and situations exist under which symmetry breaking may or may not
occur. Investigating this problem can explain why mean-field theories have been
so successful in elucidating gaseous BEC systems and when many-body effects
play a significant role. We substantiate these ideas in four distinct
situations: namely, soliton formation in attractive BECs, vortex nucleation in
rotating BECs, spontaneous magnetization in spinor BECs, and spin texture
formation in dipolar BECs.
\\ ( , 413kb)
Paper: cond-mat/0609172
Date: Thu, 7 Sep 2006 14:22:48 GMT (356kb)

Title: Reaching the hydrodynamic regime in a Bose-Einstein condensate by
   suppression of avalanche
Authors: K.M.R. van der Stam, R. Meppelink, J.M. Vogels, and P. van der Straten
Comments: Article submitted for Phys. Rev. Letters, 6 figures
Subj-class: Other
   We report the realization of a Bose-Einstein condensate (BEC) in the
hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling
at a relative low density suppressing the effect of avalanches. With the
suppression of avalanches a BEC containing 120.10^6 atoms is produced. The
collisional opacity can be tuned from the collisionless regime to a collisional
opacity of more than 3 by compressing the trap after condensation. In the
collisional opaque regime a significant heating of the cloud at time scales
shorter than half of the radial trap period is measured. This is direct proof
that the BEC is hydrodynamic.
\\ ( , 356kb)
Paper: cond-mat/0606322
replaced with revised version Thu, 7 Sep 2006 02:50:47 GMT (749kb)

Title: Finite Temperature Phase Diagram of a Two-Component Fermi Gas with
   Density Imbalance
Authors: Lianyi He, Meng Jin and Pengfei Zhuang
Comments: 12 pages, 10 figures, references added
Subj-class: Superconductivity; Other; Statistical Mechanics; Atomic Physics
\\ ( , 749kb)
Paper: cond-mat/0606398
replaced with revised version Thu, 7 Sep 2006 09:08:52 GMT (985kb)

Title: Landau damping: instability mechanism of superfluid Bose gases moving in
   optical lattices
Authors: Kiyohito Iigaya, Satoru Konabe, Ippei Danshita, and Tetsuro Nikuni
Comments: 9 pages, 5 figures
Subj-class: Other
\\ ( , 985kb)
Paper: quant-ph/0609054
Date: Thu, 7 Sep 2006 00:05:56 GMT (160kb)

Title: How to Measure the Quantum State of Collective Atomic Spin Excitation
Authors: Koji Usami, Jun-ichi Takahashi, and Mikio Kozuma
Comments: 6 pages, to appear in Phys. Rev. A
   The spin state of an atomic ensemble can be viewed as two bosonic modes,
i.e., a quantum signal mode and a $c$-numbered ``local oscillator'' mode when
large numbers of spin-1/2 atoms are spin-polarized along a certain axis and
collectively manipulated within the vicinity of the axis. We present a concrete
procedure which determines the spin-excitation-number distribution, i.e., the
diagonal elements of the density matrix in the Dicke basis for the collective
spin state. By seeing the collective spin state as a statistical mixture of the
inherently-entangled Dicke states, the physical picture of its multi-particle
entanglement is made clear.
\\ ( , 160kb)
Paper: physics/0603108
replaced with revised version Thu, 7 Sep 2006 16:05:09 GMT (247kb)

Title: Optimizing the Stark-decelerator beamline for the trapping of cold
   molecules using evolutionary strategies
Authors: Joop J. Gilijamse, Jochen K\"upper, Steven Hoekstra, Nicolas
   Vanhaecke, Sebastiaan Y. T. van de Meerakker, Gerard Meijer
Comments: 7 pages, 4 figures (RevTeX) (v2) minor corrections (v3) no changes to
   manuscript, but fix author list in arXiv abstract
Subj-class: Instrumentation and Detectors; Accelerator Physics; Atomic Physics
Journal-ref: Phys. Rev. A 73, 063410 (2006)
DOI: 10.1103/PhysRevA.73.063410
\\ ( , 247kb)
Paper: cond-mat/0609187
Date: Fri, 8 Sep 2006 02:26:15 GMT (23kb)

Title: Pairing fluctuations and the superfluid density through the BCS-BEC
Authors: E. Taylor, A. Griffin, N. Fukushima, Y. Ohashi
Comments: 30 pages
Subj-class: Other
   We derive an expression for the superfluid density of a uniform two-component
Fermi gas through the BCS-BEC crossover in terms of the thermodynamic potential
in the presence of an imposed superfluid flow. Treating the pairing
fluctuations in a Gaussian approximation following the approach of Nozi\`eres
and Schmitt-Rink, we use this definition of $\rho_s$ to obtain an explicit
result which is valid at finite temperatures and over the full BCS-BEC
crossover. It is crucial that the BCS gap $\Delta$, the chemical potential
$\mu$, and $\rho_s$ all include the effect of fluctuations at the same level in
a self-consistent manner. We show that the normal fluid density $\rho_n \equiv
n - \rho_s$ naturally separates into a sum of contributions from Fermi BCS
quasiparticles ($\rho^F_{n}$) and Bose collective modes ($\rho^B_{n}$). The
expression for $\rho^F_{n}$ is just Landau's formula for a BCS Fermi superfluid
but now calculated over the BCS-BEC crossover. The expression for the Bose
contribution $\rho^B_{n}$ is more complicated and only reduces to Landau's
formula for a Bose superfluid in the extreme BEC limit, where all the fermions
have formed stable Bose pairs and the Bogoliubov excitations of the associated
molecular Bose condensate are undamped. In a companion paper, we present
numerical calculations of $\rho_s$ using an expression equivalent to the one
derived in this paper, over the BCS-BEC crossover, including unitarity, and at
finite temperatures.
\\ ( , 23kb)
Paper: cond-mat/0609195
Date: Fri, 8 Sep 2006 10:45:52 GMT (996kb)

Title: Dirty Bosons in Disordered Optical Potentials
Authors: Pearl J.Y. Louis and Makoto Tsubota
Comments: 4 pages, 4 figures (low res)
Subj-class: Disordered Systems and Neural Networks
   In this work we systematically investigate the condensate properties,
superfluid properties and quantum phase transitions in interacting Bose gases
trapped in disordered optical potentials. We solve the Bose-Hubbard Hamiltonian
exactly for these `dirty' Bose gases for different: (a) types of disorder, (b)
disorder strengths, and (c) interatomic interactions. The three types of
disorder we study are: quasiperiodic disorder, uniform random disorder and
random speckle-type disorder. We find that the Bose glass phase, as identified
by Fisher \textit{et al.} [Phys. Rev. B {\bf 40}, 546 (1989)], contains a
normal condensate component and we show how the three different factors listed
above affect it.
\\ ( , 996kb)
Paper (*cross-listing*): physics/9802052
Date: Fri, 27 Feb 1998 15:17:57 GMT (17kb)

Title: Medium modification of two-particle scattering in nonideal Bose systems
Authors: H. Stein, K. Morawetz, and G. R\"opke
Categories: physics.atom-ph physics.acc-ph
Subj-class: Atomic Physics; Accelerator Physics; Statistical Mechanics
Journal-ref: Phys.Rev. A55 (2000) 1945
   Medium modification of scattering properties in interacting Bose systems are
considered by solving the Bethe-Salpeter equation. An equation of state for the
normal phase (generalized Beth-Uhlenbeck formula) is given using the in-medium
phase shifts to include two-particle correlations. Conclusions are drawn for
systems of bosonic atoms with repulsive interaction such as sodium $^{23}$Na
and rubidium $^{87}$Rb. It is shown that the in-medium scattering length and
the absolute value of the in-medium scattering phase shift for low scattering
energies increase with density.
\\ ( , 17kb)
Paper: cond-mat/0304358
replaced with revised version Fri, 8 Sep 2006 15:30:58 GMT (207kb)

Title: Non-Gaussian Velocity Distributions in Optical Lattices
Authors: Johan Jersblad (Department of Physics, Department of Physics), Harald
   Ellmann (Department of Physics), Kristian St\"{o}chkel (Department of
   Physics), Anders Kastberg (Department of Physics), Laurent Sanchez-Palencia
   (LKB - Lhomond), Robin Kaiser (LOD)
Comments: Final published version with 12 pages and 12 figures
Proxy: ccsd ccsd-00000311
Subj-class: Other
Journal-ref: Physical Review A 69 (2004) 013410
DOI: 10.1103/PhysRevA.69.013410
\\ ( , 207kb)
Paper: quant-ph/0608247
replaced with revised version Fri, 8 Sep 2006 00:33:27 GMT (355kb)

Title: Quantum many-body simulations using Gaussian phase-space representations
Authors: P. D. Drummond, P. Deuar, J. F. Corney
Comments: Short Review (10 pages); Corrected typo in eq (14); Added a few more
\\ ( , 355kb)
Paper: physics/0609073
Date: Fri, 8 Sep 2006 15:44:02 GMT (246kb)

Title: Dark Optical Lattice of Ring Traps for Cold Atoms
Authors: Emmanuel Courtade (PhLAM), Olivier Houde (PhLAM), Jean-Fran\c{c}ois
   Cl\'{e}ment (PhLAM), Philippe Verkerk (PhLAM), Daniel Hennequin (PhLAM)
Comments: 4 pages, submitted to PRA
Proxy: ccsd ccsd-00092344
Subj-class: Atomic Physics
   We propose a new geometry of optical lattice for cold atoms, namely a lattice
made of a 1D stack of dark ring traps. It is obtained through the interference
pattern of a standard Gaussian beam with a counter-propagating hollow beam
obtained using a setup with two conical lenses. The traps of the resulting
lattice are characterized by a high confinement and a filling rate much larger
than unity, even if loaded with cold atoms from a MOT. We have implemented this
system experimentally, and obtained a lattice of ring traps populated with
typically 40 atoms per site with a life time of 30 ms. Applications in
statistical physics, quantum computing and Bose-Einstein condensate dynamics
are conceivable.
\\ ( , 246kb)

Till next week,

Dr M. J. Davis,               Senior Lecturer in Physics
School of Physical Sciences,  email:
University of Queensland,     ph   : +61 7 334 69824
Brisbane, QLD 4072,           fax  : +61 7 336 51242
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Received on Tue Sep 12 2006 - 13:35:41 EST

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