Matt's arXiv selection: week ending 15th May 2007.

From: Matthew Davis <>
Date: Fri, 1 Jun 2007 12:16:57 +1000 (EST)

The following message was sent to the matts_arxiv list by Matthew Davis <>

For this week there were 22 new abstracts and only 5 replacements:

Date: Fri, 11 May 2007 13:36:29 GMT (134kb)

Title: FPU phenomenon for generic initial data
Authors: A. Carati, L. Galgani, A. Giorgilli, S. Paleari
Categories: cond-mat.stat-mech
   The well known FPU phenomenon (lack of attainment of equipartition of the
mode--energies at low energies, for some exceptional initial data) suggests
that the FPU model does not have the mixing property at low energies. We give
numerical indications that this is actually the case. This we show by computing
orbits for sets of initial data of full measure, sampled out from the
microcanonical ensemble by standard Montecarlo techniques. Mixing is tested by
looking at the decay of the autocorrelations of the mode--energies, and it is
found that the high--frequency modes have autocorrelations that tend instead to
positive values. Indications are given that such a nonmixing property survives
in the thermodynamic limit. It is left as an open problem whether mixing
obtains within time--scales much longer than the presently available ones.
\\ ( , 134kb)
Date: Fri, 11 May 2007 14:25:16 GMT (76kb)

Title: Functional renormalization for quantum phase transitions
Authors: C.Wetterich
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 25 pages, 1 figure
   Functional renormalization yields a simple unified description of bosons at
zero temperature, in arbitrary space dimension $d$ and for $M$ complex fields.
We concentrate on nonrelativistic bosons and an action with a linear time
derivative. The ordered phase can be associated with a nonzero density of
(quasi) particles $n$. As long as the momentum $k_{ph}$ characteristic for an
experiment remains larger than $n^{1/d}$ the quantum phase transition is
simple, with the same ``mean field'' critical exponents for all $d$ and $M$. On
the other hand, the ``Goldstone regime'' $k_{ph}\ll n^{1/d}$ reveals a rather
rich spectrum of features, depending on $d$ and $M$. In this regime one
observes for $d\lesssim 2.5$ a crossover to a relativistic action with second
time derivatives. This admits order for $d>1$, whereas $d=1$ shows a behavior
similar to the low temperature phase of the classical $O(2M)$-models.
\\ ( , 76kb)
Date: Fri, 11 May 2007 15:13:54 GMT (28kb)

Title: Dipolar gases in quasi one-dimensional geometries
Authors: S. Sinha and L. Santos
Categories: cond-mat.other
Comments: 4 pages, 3 eps figures
   We analyze the physics of cold dipolar gases in quasi one-dimensional
geometries, showing that the confinement-induced scattering resonances produced
by the transversal trapping are crucially affected by the dipole-dipole
interaction. As a consequence, the dipolar interaction may drastically change
the properties of quasi-1D dipolar condensates, even for situations in which
the dipolar interaction would be completely overwhelmed by the short-range
interactions in a 3D environment.
\\ ( , 28kb)
Date: Fri, 11 May 2007 10:14:19 GMT (498kb)

Title: Non-Markovian dynamics in atom-laser outcoupling from a double-well
   Bose-Einstein condensate
Authors: C. Lazarou, G. M. Nikolopoulos, P. Lambropoulos
Categories: quant-ph
Comments: 21 pages, 9 figure, to appear in J. Phys. B
   We investigate the dynamics of a continuous atom laser based on the merging
of independently formed atomic condensates. In a first attempt to understand
the dynamics of the system, we consider two independent elongated Bose-Einstein
condensates which approach each other and focus on intermediate inter-trap
distances so that a two-mode model is well justified. In the framework of a
mean-field theory, we discuss the quasi steady-state population of the traps as
well as the energy distribution of the outcoupled atoms.
\\ ( , 498kb)
Date: Fri, 11 May 2007 08:53:10 GMT (12kb)

Title: Accurate long-range coefficients for two excited like isotope He atoms:
   He($2 ^1P$)--He($2 ^1P$), He($2 ^1P$)--He($2 ^3P$), and He($2 ^3P$)--He($2
Authors: J.-Y. Zhang, Z.-C. Yan, D. Vrinceanu, J. F. Babb, and H. R. Sadeghpour
Categories: physics.atom-ph physics.comp-ph
   A general formalism is used to express the long-range potential energies in
inverse powers of the separation distance between two like atomic or molecular
systems with $P$ symmetries. The long-range molecular interaction coefficients
are calculated for the molecular symmetries $\Delta$, $\Pi$, and $\Sigma$,
arising from the following interactions: He($2 ^1P$)--He($2 ^1P$), He($2
^1P$)--He($2 ^3P$), and He($2 ^3P$)--He($2 ^3P$). The electric
quadrupole-quadrupole term, $C_{5}$, the van der Waals (dispersion) term
$C_{6}$, and higher-order terms, $C_{8}$, and $C_{10}$, are calculated
\textit{ab initio} using accurate variational wave functions in Hylleraas
coordinates with finite nuclear mass effects. A comparison is made with
previously published results where available.
\\ ( , 12kb)
Date: Fri, 11 May 2007 15:28:53 GMT (600kb)

Title: All optical sensor for automated magnetometry based on Coherent
   Population Trapping
Authors: J.Belfi, G.Bevilacqua, V.Biancalana, Y.Dancheva, L.Moi
Categories: physics.atom-ph physics.ins-det
Comments: 8 pages, 10 figures, appearing in JOSA B (7?) 2007
   An automated magnetometer suitable for long lasting measurement under stable
and controllable experimental conditions has been implemented. The device is
based on Coherent Population Trapping (CPT) produced by a multi-frequency
excitation. CPT resonance is observed when a frequency comb, generated by diode
laser current modulation, excites Cs atoms confined in a
$\pi/4\times(2.5)^2\times1 \textrm{cm}^3$, 2 Torr $N_2$ buffered cell. A fully
optical sensor is connected through an optical fiber to the laser head allowing
for truly remote sensing and minimization of the field perturbation. A detailed
analysis of the CPT resonance parameters as a function of the optical detuning
has been made in order to get high sensitivity measurements. The magnetic field
monitoring performances and the best sensitivity obtained in a balanced
differential configuration of the sensor are presented.
\\ ( , 600kb)
Date: Sat, 12 May 2007 21:11:30 GMT (313kb)

Title: On-top fragmentation stabilizes atom-rich attractive Bose-Einstein
Authors: Lorenz S. Cederbaum, Alexej I. Streltsov, and Ofir E. Alon
Categories: cond-mat.other
Comments: 12 pages, 4 figures
   It is well known that attractive condensates do not posses a stable ground
state in three dimensions. The widely used Gross-Pitaevskii theory predicts the
existence of metastable states up to some critical number
$N_{\mathrm{cr}}^{\mathrm{GP}}$ of atoms. It is demonstrated here that
fragmented metastable states exist for atom numbers well above
$N_{\mathrm{cr}}^{\mathrm{GP}}$. The fragments are strongly overlapping in
space. The results are obtained and analyzed analytically as well as
numerically. The implications are discussed.
\\ ( , 313kb)
Date: Mon, 14 May 2007 08:25:58 GMT (527kb)

Title: Novel Quantum Phases of Ultracold Bosonic Atoms in Optical Superlattices
Authors: Jing-Min Hou
Categories: cond-mat.other
Comments: 3 pages
   We study quantum phases of ultracold bosonic atoms in a two-dimensional
optical superlattice. The extended Bose-Hubbard model derived from the system
of ultracold bosonic atoms in an optical superlattice is solved numerically
with Gutzwiller approach. We find that supersolid(SS), density-wave(DW) phases
appear in some regimes of parameters, addition to Mott-insulator (MI) phase,
while the superfluid phase, which conventionally appears in optical
lattice-cold atom systems, is absent in this system. The experimental detection
of the first order correlations and the second order correlations of different
quantum phases with time-of-flight and noise-correlation techniques is
\\ ( , 527kb)
Date: Mon, 14 May 2007 20:00:04 GMT (42kb)

Title: Dynamics of excitations in a one-dimensional Bose liquid
Authors: M. Khodas, M. Pustilnik, A. Kamenev, L.I. Glazman
Categories: cond-mat.stat-mech cond-mat.mes-hall
   We show that the dynamic structure factor of a one-dimensional Bose liquid
has a power-law singularity defining the main mode of collective excitations.
Using the Lieb-Liniger model, we evaluate the corresponding exponent as a
function of the wave vector and the interaction strength.
\\ ( , 42kb)
Date: Mon, 14 May 2007 20:54:13 GMT (199kb)

Title: Measuring Electric Fields From Surface Contaminants with Neutral Atoms
Authors: J.M. Obrecht, R.J. Wild, E.A. Cornell
Categories: cond-mat.soft
Comments: Submitted to Physical Review A
   In this paper we demonstrate a technique of utilizing magnetically trapped
neutral $^{87}$Rb atoms to measure the magnitude and direction of electric
fields emanating from surface contaminants. We apply an alternating external
electric field that adds to (or subtracts from) the surface field in such a way
as to resonantly drive the trapped atoms into a mechanical dipole oscillation.
The growth rate of the oscillation's amplitude provides information about the
magnitude and sign of the surface field gradient. Using this measurement
technique, we are able to vectorially reconstruct the electric field produced
by surface contaminants. In addition, we can accurately measure the electric
fields generated from adsorbed atoms purposely placed onto the surface and
account for their systematic effects, which can plague a precision
surface-force measurement. We show that baking the substrate can reduce the
electric fields emanating from adsorbate, and that the mechanism for reduction
is likely surface diffusion, not desorption.
\\ ( , 199kb)
Date: Tue, 15 May 2007 02:21:36 GMT (99kb)

Title: Spectroscopic signatures of nonequilibrium pairing in atomic Fermi gases
Authors: M. Dzero, E. A. Yuzbashyan, B. L. Altshuler and P. Coleman
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 4 pages, 5 figures
   We determine the radio-frequency (RF) spectra for non-stationary states of a
fermionic condensate produced by a rapid switch of the scattering length. The
RF spectrum of the nonequilibrium state with constant BCS order parameter has
two features in contrast to equilibrium where there is a single peak. The
additional feature reflects the presence of excited pairs in the steady state.
In the state characterized by periodically oscillating order parameter
RF-absorption spectrum contains two sequences of peaks spaced by the frequency
of oscillations. Satellite peaks appear due to a process where an RF photon in
addition to breaking a pair emits/absorbs oscillation quanta.
\\ ( , 99kb)
Date: Tue, 15 May 2007 03:36:46 GMT (941kb)

Title: Analogue model of a FRW universe in Bose-Einstein condensates:
   Application of the classical field method
Authors: Piyush Jain, Silke Weinfurtner, Matt Visser, C. W. Gardiner
Categories: cond-mat.other
Comments: 26 pages, 8 figures
   Analogue models of gravity have been motivated by the possibility of
investigating phenomena not readily accessible in their cosmological
counterparts. In this paper, we investigate the analogue of cosmological
particle creation in a Friedmann-Robertson-Walker universe by numerically
simulating a Bose-Einstein condensate with a time-dependent scattering length.
In particular, we focus on a two-dimensional homogeneous condensate using the
classical field method via the truncated Wigner approximation. We show that for
various forms of the scaling function the particle production is consistent
with the underlying theory in the long wavelength limit. In this context, we
further discuss the implications of modified dispersion relations that arise
from the microscopic theory of a weakly interacting Bose gas.
\\ ( , 941kb)
Date: Tue, 15 May 2007 04:42:13 GMT (198kb)

Title: Phases and Transitions in the Spin-1 Bose-Hubbard Model: Systematics of
   a Mean-field Theory
Authors: Ramesh V. Pai, K. Sheshadri and Rahul Pandit
Categories: cond-mat.stat-mech cond-mat.other
Comments: 11 pages, 11 figures
   We generalize the mean-field theory for the spinless Bose-Hubbard model to
account for the different types of superfluid phases that can arise in the
spin-1 case. In particular, our mean-field theory can distinguish polar and
ferromagnetic superfluids, Mott insulators which arise at integer fillings at
zero temperature, and normal Bose liquids into which the Mott insulators evolve
at finite temperatures. We find, in contrast to the spinless case, that several
of the superfluid-Mott insulator transitions are first-order at finite
temperatures. Our systematic study yields rich phase diagrams that include,
first-order and second-order transitions, and a variety of tricritical points.
We discuss the possibility of realizing such phase diagrams in experimental
\\ ( , 198kb)
Date: Mon, 14 May 2007 20:22:29 GMT (184kb)

Title: Recovery of Hidden Interference in Mott Insulators
Authors: L. Tian, F. Fujiwara, T. Byrnes, and Y. Yamamoto
Categories: quant-ph
Comments: 4 figures
   Particle statistics plays a crucial role in a strongly interacting quantum
many-body system. Here, we study the Hubbard model for distinguishable
particles at unit filling. Starting from the superfluid-like state in the
strong tunneling limit and gradually reducing the tunneling so that the on-site
repulsive interaction dominates, the state ends up in a symmetric superposition
of Mott insulator states. This result can be experimentally confirmed by the
recovery of interference patterns in the density correlation functions. We also
show that this state is a maximally entangled state, in contrast to the
standard picture.
\\ ( , 184kb)
Date: Wed, 16 May 2007 10:03:45 GMT (195kb)

Title: Coherence Properties of a Bose-Einstein Condensate in an Optical
Authors: Aranya B Bhattacherjee
Categories: cond-mat.stat-mech
Comments: 12 pages, 4 figures
   We study the effect of a one dimensional optical superlattice on the
superfluid fraction, number squeezing, dynamic structure factor and the
quasi-momentum distribution of the Mott-insulator. We show that due to the
secondary lattice,there is a decrease in the superfluid fraction and the number
fluctuation. The dynamic structure factor which can be measured by Bragg
spectroscopy is also suppressed due to the addition of the secondary lattice.
The visibility of the interference pattern (the quasi-momentum distribution)of
the Mott-insulator is found to decrease due to the presence of the secondary
lattice. Our results have important implications in atom interferometry and
quantum computation in optical lattices.
\\ ( , 195kb)
Date: Wed, 16 May 2007 11:13:51 GMT (7kb)

Title: The Localization Length of Stationary States in the Nonlinear
   Schreodinger Equation
Authors: Alexander Iomin and Shmuel Fishman
Categories: cond-mat.dis-nn
   For the nonlinear Schreodinger equation (NLSE), in presence of disorder,
exponentially localized stationary states are found. In the present Letter it
is demonstrated analytically that the localization length is typically
independent of the strength of the nonlinearity and is identical to the one
found for the corresponding linear equation. The analysis makes use of the
correspondence between the stationary NLSE and the Langevin equation as well as
of the resulting Fokker-Planck equation. The calculations are performed for the
``white noise'' random potential and an exact expression for the exponential
growth of the eigenstates is obtained analytically. It is argued that the main
conclusions are robust.
\\ ( , 7kb)
Date: Wed, 16 May 2007 10:46:46 GMT (25kb)

Title: Finite temperature effects in light scattering off Cooper-paired Fermi
Authors: Bimalendu Deb
Categories: cond-mat.other cond-mat.supr-con
Comments: 18 pages, 4 figures, Accepted in J. Phys. B: At. Mol. & Opt. Phys
   We study stimulated light scattering off a superfluid Fermi gas of atoms at
finite temperature. We derive response function that takes into account vertex
correction due to final state interactions; and analyze finite temperature
effects on collective and quasiparticle excitations of a uniform superfluid
Fermi gas. Light polarization is shown to play an important role in
excitations. Our results suggest that it is possible to excite
Bogoliubov-Anderson phonon at a large scattering length by light scattering.
\\ ( , 25kb)
Date: Tue, 15 May 2007 20:00:29 GMT (65kb)

Title: Conditions for the Quantum to Classical Transition: Trajectories vs.
   Phase Space Distributions
Authors: Benjamin D. Greenbaum, Kurt Jacobs, Bala Sundaram
Categories: quant-ph
Comments: 6 pages, revtex4, 2 eps figures
   We contrast two sets of conditions that govern the transition in which
classical dynamics emerges from the evolution of a quantum system. The first
was derived by considering the trajectories seen by an observer (dubbed the
"strong" transition) [Bhattacharya et al., Phys. Rev. Lett. 85, 4852 (2000)],
and the second by considering phase-space densities (the ``weak'' transition)
[Greenbaum et al., Chaos 15, 033302 (2005)]. On the face of it these conditions
appear rather different. We show, however, that in the semiclassical regime, in
which the action of the system is large compared to hbar, and the environmental
(or measurement) noise is small, they have an almost identical form. In this
regime, the weak conditions dominate while in the opposite regime where the
action is not much larger that hbar, the strong conditions dominate.
\\ ( , 65kb)
Date: Wed, 16 May 2007 17:17:35 GMT (725kb)

Title: Pulsed beams as field probes for precision measurement
Authors: J. J. Hudson, H. T. Ashworth, D. M. Kara, M. R. Tarbutt, B. E. Sauer,
   E. A. Hinds
Categories: physics.atom-ph
Comments: 6 pages, 12 figures. Figures heavily compressed to comply with
   arxiv's antediluvian file-size policy
   We describe a technique for mapping the spatial variation of static electric,
static magnetic, and rf magnetic fields using a pulsed atomic or molecular
beam. The method is demonstrated using a beam designed to measure the electric
dipole moment of the electron. We present maps of the interaction region,
showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm
with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with
25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm
resolution. This new diagnostic technique is very powerful in the context of
high-precision atomic and molecular physics experiments, where pulsed beams
have not hitherto found widespread application.
\\ ( , 725kb)
Date: Wed, 16 May 2007 20:04:00 GMT (31kb)

Title: Vortex Lattice Locking in Rotating Two-Component Bose-Einstein
Authors: Ryan Barnett, Gil Refael, Mason A. Porter, Hans Peter Buchler
Categories: cond-mat.str-el cond-mat.mes-hall
Comments: 4.2 pages
   We examine the effect of vortex locking in two-component Bose-Einstein
condensates composed of atoms with different masses. For the case of negative
interspecies interaction g_{12}<0, we demonstrate the stability of locked
phases, in which the vortices of the two components form bound pairs. We show
that such a state requires that the superfluids of both components and the
vortex lattice all rotate at different rates. We find that the Magnus force
pulling apart bound pairs of vortices increases linearly with the distance from
the center of the condensate and eventually overwhelms the restoring force
arising from the interspecies interaction. We provide a prediction for the
critical radius at which vortices become unbound and support our analysis with
numerical minimizations.
\\ ( , 31kb)
Date: Thu, 17 May 2007 11:43:29 GMT (125kb)

Title: Spectroscopy of Strong-Pulse Superradiance in a Bose-Einstein condensate
Authors: Nir Bar-Gill, Eitan E. Rowen and Nir Davidson
Categories: cond-mat.other
   We study experimentally superradiance in a Bose-Einstein condensate using a
two-frequency pump beam. By controlling the frequency difference between the
beam components, we measure the spectrum of the backward (energy-mismatched)
superradiant atomic modes. In addition, we show that the populations of these
modes display coherent time-dynamics. These results are compared to a
semi-classical model based on coupled Schroedinger-Maxwell equations.
\\ ( , 125kb)
Date: Thu, 17 May 2007 17:38:21 GMT (488kb)

Title: A self-biased permanent magnet atom chip for Bose-Einstein condensation
Authors: T. Fernholz, R. Gerritsma, S. Whitlock, I. Barb, R. J. C. Spreeuw
Categories: cond-mat.other
   We describe a self-biased, fully permanent magnet atom chip used to study
ultracold atoms and to produce a Bose-Einstein condensate (BEC). The magnetic
trap is loaded efficiently by adiabatic transport of a magnetic trap via the
application of uniform external fields. Radio frequency spectroscopy is used
for in-trap analysis and to determine the temperature of the atomic cloud. The
formation of a Bose-Einstein condensate is observed in time of flight images
and as a narrow peak appearing in the radio frequency spectrum.
\\ ( , 488kb)


replaced with revised version Mon, 14 May 2007 16:34:50 GMT (214kb)

Title: Fourier synthesis of optical potentials for atomic quantum gases
Authors: Gunnar Ritt, Carsten Geckeler, Tobias Salger, Giovanni Cennini, Martin
Categories: cond-mat.other
Comments: 4 figures
Journal-ref: Phys. Rev. A 74, 063622 (2006)
DOI: 10.1103/PhysRevA.74.063622
\\ ( , 214kb)
replaced with revised version Mon, 14 May 2007 02:49:36 GMT (278kb)

Title: Large-N expansion for unitary superfluid Fermi gases
Authors: M. Y. Veillette, D. E. Sheehy, and L. Radzihovsky
Categories: cond-mat.other
Comments: 13 pages
Journal-ref: Phys. Rev. A 75, 043614 (2007).
DOI: 10.1103/PhysRevA.75.043614
\\ ( , 278kb)
replaced with revised version Mon, 14 May 2007 10:16:55 GMT (71kb)

Title: Phase Transitions and Pairing Signature in Strongly Attractive Fermi
   Atomic Gases
Authors: X W Guan, M T Batchelor, C Lee and M Bortz
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 9 pages, 5 figures, expanded version with additional text, references
   and figures
\\ ( , 71kb)
replaced with revised version Mon, 14 May 2007 09:39:55 GMT (20kb)

Title: Quantum rearrangement and self-consistent BCS-BEC crossover
Authors: Ji-sheng Chen, Chuan-ming Cheng, Jia-rong Li, Yan-ping Wang
Categories: cond-mat.stat-mech hep-ph nucl-th
Comments: 5 pages, 1 figure; shortened version with typos fixed and references
\\ ( , 20kb)
replaced with revised version Thu, 17 May 2007 19:56:57 GMT (339kb)

Title: Vortex proliferation in the Berezinskii-Kosterlitz-Thouless regime on a
   two-dimensional lattice of Bose-Einstein condensates
Authors: V. Schweikhard, S. Tung, and E. A. Cornell
Categories: cond-mat.mes-hall
Comments: changed title; changed definition of vortex density surrogate "D";
   additional data in Fig. 3; text revisions
\\ ( , 339kb)

Till next time,

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
Matt's arXiv selection: weekly summary of cold-atom papers from
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Received on Fri Jun 01 2007 - 12:16:57 EST

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