Matt's arXiv selection: week ending 20th July 2007.

From: Matthew Davis <>
Date: Tue, 31 Jul 2007 15:50:52 +1000 (EST)

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

Hi all,

There were 35 new preprints and 13 replacements this week.

Date: Thu, 12 Jul 2007 21:16:14 GMT (10kb)

Title: Soluble Models of Strongly Interacting Two-level Ultracold Gases in
   Tight Waveguides with Coupling to the Quantized Electromagnetic Field
Authors: M. D. Girardeau
Categories: cond-mat.other
Comments: 4 pages, no figures, revtex4. Submitted to Phys. Rev. Lett
   A generalized Fermi-Bose mapping method is used to determine the exact ground
states of six models of strongly interacting ultracold gases of two-level atoms
in tight waveguides, which are generalizations of the Tonks-Girardeau (TG) gas
(1D Bose gas with point hard cores) and fermionic Tonks-Girardeau (FTG) gas (1D
spin-aligned Fermi gas with infinitely strong zero-range attractions). Three of
these models exhibit a quantum phase transition in the presence of an external
magnetic field, associated with a cooperative ground state rearrangement
wherein Fermi energy is traded for internal excitation energy. After
investigation of these models in the absence of an electromagnetic field, one
is generalized to include resonant interactions with a single photon mode,
leading to a possible thermal phase transition associated with Dicke
\\ ( , 10kb)
Date: Fri, 13 Jul 2007 06:59:59 GMT (120kb)

Title: Shear viscosity and Bose statistics: Capillary flow above lambda point
Authors: Shun-ichiro Koh
Categories: cond-mat.supr-con cond-mat.stat-mech
Comments: 32pages, 7figures
   The gradual fall of the shear viscosity below 2.8K, observed in a liquid
helium 4 flowing through a capillary, is examined. The disappearance of the
shear viscosity in a capillary flow is a manifestation of superfluidity in
dissipative phenomena, the onset mechanism of which is a subtle problem
compared to that of superfluidity in non-dissipative phenomena. Applying the
linear-response theory to the reciprocal of the shear viscosity coefficient, we
relate these two types of superfluidity using the Kramers-Kronig relation. We
obtain a formula describing the influence of Bose statistics on the kinematic
shear viscosity in terms of the susceptibility. Compared to an ordinary liquid,
a liquid helium 4 above the lambda point has a 1/1000 times smaller shear
viscosity coefficient. Hence, although in the normal phase, it is already an
anomalous liquid under the strong influence of Bose statistics. The coherent
many-body wave function grows to an intermediate size between a macroscopic and
a microscopic one, not as a thermal fluctuation but as a thermal equilibrium
state. Beginning with bosons without the condensate, we make a perturbation
calculation of its susceptibility with respect to the repulsive interaction. We
examine how, with decreasing temperature, the growth of the coherent wave
function gradually suppresses the shear viscosity, and finally leads to a
frictionless flow at the lambda-point.
\\ ( , 120kb)
Date: Fri, 13 Jul 2007 16:54:31 GMT (21kb)

Title: Nonlinear coherent transport of waves in disordered media
Authors: Thomas Wellens, Benoit Gremaud
Categories: cond-mat.mes-hall cond-mat.dis-nn
Comments: 4 pages, 3 figures
   We present a diagrammatic theory for coherent backscattering from disordered
dilute media in the nonlinear regime. The approach is non-perturbative in the
strength of the nonlinearity. We show that the coherent backscattering
enhancement factor is strongly affected by the nonlinearity, and corroborate
these results by numerical simulations. Our theory can be applied to several
physical scenarios like scattering of light in nonlinear Kerr media, or
propagation of matter waves in disordered potentials.
\\ ( , 21kb)
Date: Fri, 13 Jul 2007 11:32:34 GMT (354kb)

Title: Interacting bosons in an optical lattice
Authors: Ch. Moseley, O. Fialko, K. Ziegler
Categories: cond-mat.other
Comments: 58 pages, 14 figures
   Several models of a strongly interacting Bose gas in an optical lattice are
studied within the functional-integral approach. The one-dimensional Bose gas
is briefly discussed. Then the Bose-Einstein condensate and the Mott insulator
of a three-dimensional Bose gas are described in mean-field approximation, and
the corresponding phase diagrams are evaluated. Other characteristic
quantities, like the spectrum of quasiparticle excitations and the static
structure factor, are obtained from Gaussian fluctuations around the mean-field
solutions. We discuss the role of quantum and thermal fluctuations, and
determine the behavior of physical quantities in terms of density and
temperature of the Bose gas. In particular, we study the dilute limit, where
the mean-field equation becomes the Gross-Pitaevskii equation. This allows us
to extend the Gross-Pitaevskii equation to the dense regime by introducing
renormalized parameters in the latter.
\\ ( , 354kb)
Date: Fri, 13 Jul 2007 11:38:57 GMT (153kb)

Title: Atomic Landau-Zener tunneling in Fourier-synthesized optical lattices
Authors: Tobias Salger, Carsten Geckeler, Sebastian Kling, Martin Weitz
Categories: cond-mat.other
Comments: 11 pages, 5 figures
   We report on an experimental study of quantum transport of atoms in variable
periodic optical potentials. The band structure of both ratchet-type asymmetric
and symmetric lattice potentials is explored. The variable atom potential is
realized by superimposing a conventional standing wave potential of \lambda/2
spatial periodicity with a fourth-order multiphoton potential of \lambda /4
periodicity. We find that the Landau-Zener tunneling rate between the first and
the second excited Bloch band depends critically on the relative phase between
the two spatial lattice harmonics.
\\ ( , 153kb)
Date: Fri, 13 Jul 2007 12:50:48 GMT (20kb)

Title: Decoherence of a particle in a ring
Authors: Doron Cohen and Baruch Horovitz
Categories: cond-mat.mes-hall
Comments: 5 pages, 1 figure
   We consider a particle coupled to a dissipative environment and derive a
perturbative formula for the dephasing rate based on the purity of the reduced
probability matrix. We apply this formula to the problem of a particle on a
ring, that interacts with a dirty metal environment. At low but finite
temperatures we find a dephasing rate $\propto T^{3/2}$, and identify dephasing
lengths for large and for small rings. These findings shed light on recent
Monte Carlo data regarding the effective mass of the particle. At zero
temperature we find that spatial fluctuations suppress the possibility of
having a power law decay of coherence.
\\ ( , 20kb)
Date: Fri, 13 Jul 2007 11:00:51 GMT (188kb)

Title: Observation of Electromagnetically Induced Transparency for a Squeezed
   Vacuum with the Time Domain Method
Authors: M. Arikawa, K. Honda, D. Akamatsu, Y. Yokoi, K. Akiba, S. Nagatsuka,
   A. Furusawa, and M. Kozuma
Categories: quant-ph
   A probe light in a squeezed vacuum state was injected into cold 87Rb atoms
with an intense control light in a coherent state. A sub-MHz window was created
due to electromagnetically induced transparency, and the incident squeezed
vacuum could pass through the cold atoms without optical loss, as was
successfully monitored using a time-domain homodyne method.
\\ ( , 188kb)
Date: Fri, 13 Jul 2007 15:28:11 GMT (77kb)

Title: Self-cooling of a movable mirror to the ground state using radiation
Authors: Aurelien Dantan (University of Aarhus), Claudiu Genes (Universita Di
   Camerino), David Vitali (Universita Di Camerino), Michel Pinard (LKB -
Categories: quant-ph
Comments: 4 pages, 3 figures
Proxy: ccsd hal-00162568
   We show that one can cool a micro-mechanical oscillator to its quantum ground
state using radiation pressure in an appropriately detuned cavity
(self-cooling). From a simple theory based on Heisenberg-Langevin equations we
find that optimal self-cooling occurs in the good cavity regime, when the
cavity bandwidth is smaller than the mechanical frequency, but still larger
than the effective mechanical damping. In this case the intracavity field and
the vibrational mechanical mode coherently exchange their fluctuations. We also
present dynamical calculations which show how to access the mirror final
temperature from the fluctuations of the field reflected by the cavity.
\\ ( , 77kb)
Date: Fri, 13 Jul 2007 03:39:40 GMT (433kb)

Title: Lattice with a Twist : Helical Waveguides for Ultracold Matter
Authors: M. Bhattacharya
Categories: physics.atom-ph physics.optics
Comments: Accepted for publication in Optics Communications
   We investigate the waveguiding properties of the optical interference pattern
of two counter-propagating Laguerre-Gaussian beams. The number, helicity,
radius, pitch, depth and frequencies of transverse confinement of the
waveguides are simply related to the beam parameters. Quantitative connections
to the familiar Gaussian optical lattice are made and an application to quantum
transport is suggested.
\\ ( , 433kb)
Date: Fri, 13 Jul 2007 14:11:18 GMT (167kb)

Title: Trapping of ultracold polar molecules with a Thin Wire Electrostatic
Authors: J. Kleinert, C. Haimberger, P. J. Zabawa, and N. P. Bigelow
Categories: physics.atom-ph
Comments: 4 pages, 3 figures
   We describe the realization of a DC electric field trap for ultracold polar
molecules, the Thin WIre electroStatic Trap (TWIST). The thin wires that form
the electrodes of the TWIST allow us to superimpose the trap onto a
magneto-optical trap (MOT). In our experiment, ultracold polar NaCs molecules
in their electronic ground state are created in the MOT via photoassociation,
achieving a continuous accumulation in the TWIST of molecules in low-field
seeking states. Initial measurements show that the TWIST trap lifetime is
limited only by the background pressure in the chamber.
\\ ( , 167kb)
Date: Fri, 13 Jul 2007 02:51:52 GMT (427kb)

Title: Dispersive, superfluid-like shock waves in nonlinear optics
Authors: Wenjie Wan, Shu Jia, and Jason W. Fleischer
Categories: physics.optics physics.flu-dyn
Comments: 21 pages, 6 figures Revised abstract
Journal-ref: Nature Physics 3, 46 (2007)
   In most classical fluids, shock waves are strongly dissipative, their energy
being quickly lost through viscous damping. But in systems such as cold
plasmas, superfluids, and Bose-Einstein condensates, where viscosity is
negligible or non-existent, a fundamentally different type of shock wave can
emerge whose behaviour is dominated by dispersion rather than dissipation.
Dispersive shock waves are difficult to study experimentally, and analytical
solutions to the equations that govern them have only been found in one
dimension (1D). By exploiting a well-known, but little appreciated,
correspondence between the behaviour of superfluids and nonlinear optical
materials, we demonstrate an all-optical experimental platform for studying the
dynamics of dispersive shock waves. This enables us to observe the propagation
and nonlinear response of dispersive shock waves, including the interaction of
colliding shock waves, in 1D and 2D. Our system offers a versatile and more
accessible means for exploring superfluid-like and related dispersive
\\ ( , 427kb)
Date: Fri, 13 Jul 2007 20:02:17 GMT (47kb)

Title: A quantum topological phase transition at the microscopic level
Authors: Claudio Castelnovo (1), and Claudio Chamon (2). ((1) Oxford
   University, (2) Boston University)
Categories: cond-mat.str-el
Comments: (13 pages, 4 figures)
   We study a quantum phase transition between a phase which is topologically
ordered and one which is not. We focus on a spin model, an extension of the
toric code, for which we obtain the exact ground state for all values of the
coupling constant that takes the system across the phase transition. We compute
the entanglement and the topological entropy of the system as a function of
this coupling constant, and show that the topological entropy remains constant
all the way up to the critical point, and jumps to zero beyond it. Despite the
jump in the topological entropy, the transition is second order as detected via
any local observable.
\\ ( , 47kb)
Date: Fri, 13 Jul 2007 23:21:34 GMT (262kb)

Title: Bose-Einstein condensation in an optical lattice
Authors: P. B. Blakie and Wen-Xin Wang
Categories: cond-mat.other
Comments: 10 pages, 5 figures
   In this paper we develop an analytic expression for the critical temperature
for a gas of ideal bosons in a combined harmonic lattice potential, relevant to
current experiments using optical lattices. We give corrections to the critical
temperature arising from effective mass modifications of the low energy
spectrum, finite size effects and excited band states. We compute the critical
temperature using numerical methods and compare to our analytic result. We
study condensation in an optical lattice over a wide parameter regime and
demonstrate that the critical temperature can be increased or reduced relative
to the purely harmonic case by adjusting the harmonic trap frequency. We show
that a simple numerical procedure based on a piecewise analytic density of
states provides an accurate prediction for the critical temperature.
\\ ( , 262kb)
Date: Sun, 15 Jul 2007 10:34:30 GMT (329kb)

Title: The single-particle density matrix and the momentum distribution of dark
   "solitons" in a Tonks-Girardeau gas
Authors: H. Buljan, K. Lelas, R. Pezer, and M. Jablan
Categories: cond-mat.other
Comments: 9 pages, 8 figures
   We study the reduced single-particle density matrix (RSPDM), the momentum
distribution, natural orbitals and their occupancies, of dark "soliton" (DS)
states in a Tonks-Girardeau gas. DS states are specially tailored excited
many-body eigenstates, which have a dark solitonic notch in their
single-particle density. The momentum distribution of DS states has a
characteristic shape with two sharp spikes. We find that the two spikes arise
due to the high degree of correlation observed within the RSPDM between the
mirror points ($x$ and $-x$) with respect to the dark notch at $x=0$; the
correlations oscillate rather than decay as the points $x$ and $-x$ are being
\\ ( , 329kb)
Date: Sun, 15 Jul 2007 22:42:56 GMT (81kb)

Title: Dissipative Dynamics of Matter Wave Soliton in Nonlinear Optical Lattice
Authors: F.Kh. Abdullaev, A. Gammal, H.L.F. da Luz, and Lauro Tomio
Categories: cond-mat.other
Comments: 9 pages, 8 figures
   Dynamics and stability of solitons in two-dimensional (2D) Bose-Einstein
condensates (BEC), with low-dimensional (1D) conservative plus dissipative
nonlinear optical lattices are investigated. In the case of focusing media
(with attractive atomic systems) the collapse of the wave packet is arrested by
the dissipative periodic nonlinearity. The adiabatic variation of the
background scattering length leads to metastable matter-wave solitons.
   When the atom feeding mechanism is used, a dissipative soliton can exist in
focusing 2D media with 1D periodic nonlinearity. In the defocusing media
(repulsive BEC case) with harmonic trap in one dimension and one dimensional
nonlinear optical lattice in other direction, the stable soliton can exist.
This prediction of variational approach is confirmed by the full numerical
simulation of 2D Gross-Pitaevskii equation.
\\ ( , 81kb)
Date: Mon, 16 Jul 2007 12:11:01 GMT (8kb)

Title: A microcanonical quantum fluctuation theorem
Authors: Peter Talkner, Peter Hanggi, Manuel Morillo
Categories: cond-mat.stat-mech
   Previously derived expressions for the characteristic function of work
performed on a quantum system by a classical external force are generalized to
arbitrary initial states of the considered system and to Hamiltonians with
degenerate spectra. In the particular case of microcanonical initial states a
fluctuation theorem is derived which relates averages of shifted inverse work
describing an out of equilibrium process to equilibrium entropies of
microcanonical states.
\\ ( , 8kb)
Date: Mon, 16 Jul 2007 16:33:49 GMT (213kb)

Title: Critical velocity for superfluid flow across the BEC-BCS crossover
Authors: D. E. Miller, J. K. Chin, C. A. Stan, Y. Liu, W. Setiawan, C. Sanner
   and W. Ketterle
Categories: cond-mat.other
   Critical velocities have been observed in an ultracold superfluid Fermi gas
throughout the BEC-BCS crossover. A pronounced peak of the critical velocity at
unitarity demonstrates that superfluidity is most robust for resonant atomic
interactions. Critical velocities were determined from the abrupt onset of
dissipation when the velocity of a moving one dimensional optical lattice was
varied. The dependence of the critical velocity on lattice depth and on the
inhomogeneous density profile was studied.
\\ ( , 213kb)
Date: Mon, 16 Jul 2007 16:52:12 GMT (117kb)

Title: Manufacturing a thin wire electrostatic trap (TWIST) for ultracold polar
Authors: J. Kleinert, C. Haimberger, P. J. Zabawa, and N. P. Bigelow
Categories: physics.atom-ph
Comments: 3 pages, 2 figures
   We present a detailed description on how to build a Thin WIre electroStatic
Trap (TWIST) for ultracold polar molecules which can be superimposed onto a
magneto optical trap. The required parts are easily accessible and inexpensive
(bill of parts $<$\$1000). A machine shop, a protected atmosphere glove box,
and a fume hood are sufficient to manufacture the TWIST.
\\ ( , 117kb)
Date: Sat, 14 Jul 2007 23:04:59 GMT (91kb)

Title: Stimulated radiative laser cooling
Authors: Peter Muys
Categories: physics.optics
   Building a refrigerator based on the conversion of heat into optical energy
is an ongoing engineering challenge. Under well-defined conditions, spontaneous
anti-Stokes fluorescence of a dopant material in a host matrix is capable of
lowering the host temperature. The fluorescence is conveying away a part of the
thermal energy stored in the vibrational oscillations of the host lattice. In
particular, applying this principle to the cooling of (solid-state) lasers
opens up many potential device applications, especially in the domain of
high-power lasers. In this paper, an alternative optical cooling scheme is
outlined, leading to radiative cooling of solid-state lasers. It is based on
converting the thermal energy stored in the host, into optical energy by means
of a stimulated nonlinear process, rather than a spontaneous process. This
should lead to better cooling efficiencies and a higher potential of applying
the principle for device applications.
\\ ( , 91kb)
Date: Mon, 16 Jul 2007 20:00:16 GMT (428kb)

Title: Trionic phase of ultracold fermions in an optical lattice: a variational
Authors: Akos Rapp, Walter Hofstetter, and Gergely Zarand
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 14 PRB pages, 8 figures
   To investigate ultracold fermionic atoms of three internal states (colors) in
an optical lattice, subject to strong attractive interaction, we study the
attractive three-color Hubbard model in infinite dimensions using a variational
approach. We find a quantum phase transition between a weak coupling
superconducting phase and a strong coupling trionic phase where groups of three
atoms are bound to a composite fermion. We show how the Gutzwiller variational
theory can be reformulated in terms of an effective field theory with
three-body interactions, and how this effective field theory can be solved
exactly in infinite dimensions using the methods of dynamical mean field
\\ ( , 428kb)
Date: Mon, 16 Jul 2007 20:16:41 GMT (152kb)

Title: Superfluid-insulator transitions of the Fermi gas with near-unitary
   interactions in a periodic potential
Authors: Eun Gook Moon, Predrag Nikolic, and Subir Sachdev
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 5 pages, 3 figures
   We consider spin-1/2 fermions of mass m with interactions near the unitary
limit. In an applied periodic potential of amplitude V and period a, and with a
density of an even integer number of fermions per unit cell, there is a
second-order quantum phase transition between superfluid and insulating ground
states at a critical V=Vc. We compute the universal ratio Vc m a^2 / h^2 at
N=infinity in a model with Sp(2N) spin symmetry. The insulator interpolates
between a band insulator of fermions and a Mott insulator of fermion pairs. We
discuss implications for recent experiments.
\\ ( , 152kb)
Date: Tue, 17 Jul 2007 02:54:30 GMT (286kb)

Title: Excitation spectrum of bosons in a finite one-dimensional circular
   waveguide via the Bethe ansatz
Authors: Andrew G. Sykes, Peter D. Drummond and Matthew J. Davis
Categories: cond-mat.other cond-mat.stat-mech
Comments: 13 pages, 12 figures
   The exactly solvable Lieb-Liniger model of interacting bosons in
one-dimension has attracted renewed interest as current experiments with
ultra-cold atoms begin to probe this regime. Here we numerically solve the
equations arising from the Bethe ansatz solution for the exact many-body wave
function in a finite-size system of up to twenty particles for attractive
interactions. We discuss the novel features of the solutions, and how they
deviate from the well-known string solutions [H. B. Thacker, Rev. Mod. Phys.\
\textbf{53}, 253 (1981)] at finite densities. We present excited state string
solutions in the limit of strong interactions and discuss their physical
interpretation, as well as the characteristics of the quantum phase transition
that occurs as a function of interaction strength in the mean-field limit.
Finally we compare our results to those of exact diagonalization of the
many-body Hamiltonian in a truncated basis. We also present excited state
solutions and the excitation spectrum for the repulsive 1D Bose gas on a ring.
\\ ( , 286kb)
Date: Tue, 17 Jul 2007 05:16:43 GMT (124kb)

Title: Effective mean-field equations for cigar-shaped and disk-shaped
   Bose-Einstein condensates
Authors: A. Mu\~noz Mateo and V. Delgado (Univ. de La Laguna)
Categories: cond-mat.other
Comments: 10 pages, 8 figures
   By applying the standard adiabatic approximation and using the accurate
analytical expression for the corresponding local chemical potential obtained
in our previous work [Phys. Rev. A \textbf{75}, 063610 (2007)] we derive an
effective 1D equation that governs the axial dynamics of mean-field
cigar-shaped condensates with repulsive interatomic interactions, accounting
accurately for the contribution from the transverse degrees of freedom. This
equation, which is more simple than previous proposals, is also more accurate.
Moreover, it allows treating condensates containing an axisymmetric vortex with
no additional cost. Our effective equation also has the correct limit in both
the quasi-1D mean-field regime and the Thomas-Fermi regime and permits one to
derive fully analytical expressions for ground-state properties such as the
chemical potential, axial length, axial density profile, and local sound
velocity. These analytical expressions remain valid and accurate in between the
above two extreme regimes. Following the same procedure we also derive an
effective 2D equation that governs the transverse dynamics of mean-field
disk-shaped condensates. This equation, which also has the correct limit in
both the quasi-2D and the Thomas-Fermi regime, is again more simple and
accurate than previous proposals. We have checked the validity of our equations
by numerically solving the full 3D Gross-Pitaevskii equation.
\\ ( , 124kb)
Date: Tue, 17 Jul 2007 13:17:38 GMT (484kb)

Title: Generalized Neighbor-Interaction Models Induced by Nonlinear Lattices
Authors: F. Kh. Abdullaev, Yu. V. Bludov, S. V. Dmitriev, P. G. Kevrekidis, V.
   V. Konotop
Categories: cond-mat.other
   It is shown that the tight-binding approximation of the nonlinear
Schr\"odinger equation with a periodic linear potential and periodic in space
nonlinearity coefficient gives rise to a number of nonlinear lattices with
complex, both linear and nonlinear, neighbor interactions. The obtained
lattices present non-standard possibilities, among which we mention a
quasi-linear regime, where the pulse dynamics obeys essentially the linear
Schr{\"o}dinger equation. We analyze the properties of such models both in
connection with their modulational stability, as well as in regard to the
existence and stability of their localized solitary wave solutions.
\\ ( , 484kb)
Date: Tue, 17 Jul 2007 17:15:47 GMT (496kb)

Title: Dynamical and energetic instabilities in multi-component Bose-Einstein
   condensates in optical lattices
Authors: J. Ruostekoski and Zachary Dutton
Categories: cond-mat.other
Comments: 17 pages, 12 figures. Submitted to Phys. Rev. A
   We study dynamical and energetic instabilities in the transport properties of
Bloch waves for atomic multi-component Bose-Einstein condensates in optical
lattices in the tight-binding limit. We obtain stability criteria analytically,
as a function of superfluid velocities and interaction parameters, in several
cases for two-component and spinor condensates. In the two-species case we find
that the presence of the other condensate component can stabilize the
superfluid flow of an otherwise unstable condensate and that the free space
dynamical miscibility condition of the two species can be reversed by tuning
the superfluid flow velocities. In spin-1 condensates, we find the steady-state
Bloch wave solutions and characterize their stability criteria. We find
generally more regions of dynamical instability arise for the polar than for
the ferromagnetic solutions. In the presence of magnetic Zeeman shifts, we find
a richer variety of condensate solutions and find that the linear Zeeman shift
can stabilize the superfluid flow in several cases of interest.
\\ ( , 496kb)
Date: Tue, 17 Jul 2007 17:23:03 GMT (361kb)

Title: Is a gas of strongly interacting atomic fermions a nearly perfect fluid?
Authors: A. Turlapov, J. Kinast, B. Clancy, Le Luo, J. Joseph and J. E. Thomas
Categories: cond-mat.other
Comments: 10 pages, 5 figures
   We use all-optical methods to produce a highly-degenerate Fermi gas of
spin-1/2 $^6$Li atoms. A magnetic field tunes the gas near a collisional
(Feshbach) resonance, producing strong interactions between spin-up and
spin-down atoms. This atomic gas is a paradigm for strong interactions in
nature, and provides tests of current quantum many-body calculational methods
for diverse systems, including very high temperature superconductors, nuclear
matter in neutron stars, and the quark-gluon plasma of the Big Bang. We have
measured properties of a breathing mode over a wide range of temperatures. At
temperatures both below and well above the superfluid transition, the frequency
of the mode is nearly constant and very close to the hydrodynamic value.
However, explaining both the frequency and the damping rate in the normal
collisional regime has not been achieved. Our measurements of the damping rate
as a function of the energy of the gas are used to estimate an upper bound on
the viscosity. Using our new measurements of the entropy of the gas, we
estimate the ratio of the shear viscosity to the entropy density, and compare
the result with the lower bound for quantum viscosity recently predicted using
string theory methods.
\\ ( , 361kb)
Date: Mon, 16 Jul 2007 21:31:44 GMT (24kb)

Title: Production of mesoscopic superpositions with ultracold atoms
Authors: H. T. Ng
Categories: quant-ph
Comments: 4 pages, 2 figures
   We study mesoscopic superpositions of two component Bose-Einstein
condensates. Atomic condensates, with long coherence times, are good systems in
which to study such quantum phenomenon. We show that the mesoscopic
superposition states can be rapidly generated in which the atoms dispersively
interact with the photon field in a cavity. We also discuss the production of
compass states which are generalized Schr\"{o}dinger cat states. The physical
realization of mesoscopic states is important in studying decoherence and
precision measurement.
\\ ( , 24kb)
Date: Tue, 17 Jul 2007 13:56:52 GMT (167kb)

Title: Enhancement of the formation of ultracold $^{85}$Rb$_2$ molecules due to
   resonant coupling
Authors: H. K. Pechkis, D. Wang, Y. Huang, E. E. Eyler, P. L. Gould, W. C.
   Stwalley, and C. P. Koch
Categories: physics.atom-ph
Comments: 6 pages, 5 figures; corrected author list
   We have studied the effect of resonant electronic state coupling on the
formation of ultracold ground-state $^{85}$Rb$_2$. Ultracold Rb$_2$ molecules
are formed by photoassociation (PA) to a coupled pair of $0_u^+$ states,
$0_u^+(P_{1/2})$ and $0_u^+(P_{3/2})$, in the region below the $5S+5P_{1/2}$
limit. Subsequent radiative decay produces high vibrational levels of the
ground state, $X ^1\Sigma_g^+$. The population distribution of these $X$ state
vibrational levels is monitored by resonance-enhanced two-photon ionization
through the $2 ^1\Sigma_u^+$ state. We find that the populations of vibrational
levels $v''$=112$-$116 are far larger than can be accounted for by the
Franck-Condon factors for $0_u^+(P_{1/2}) \to X ^1\Sigma_g^+$ transitions with
the $0_u^+(P_{1/2})$ state treated as a single channel. Further, the
ground-state molecule population exhibits oscillatory behavior as the PA laser
is tuned through a succession of $0_u^+$ state vibrational levels. Both of
these effects are explained by a new calculation of transition amplitudes that
includes the resonant character of the spin-orbit coupling of the two $0_u^+$
states. The resulting enhancement of more deeply bound ground-state molecule
formation will be useful for future experiments on ultracold molecules.
\\ ( , 167kb)
Date: Wed, 18 Jul 2007 03:09:49 GMT (34kb)

Title: Radio Frequency Spectroscopy of Trapped Fermi Gases with Population
Authors: Yan He, Chih-Chun Chien, Qijin Chen, and K. Levin
Categories: cond-mat.str-el cond-mat.supr-con
Comments: 4 page, 3 figures, submitted to PRA Rapid
   We address radio frequency (RF) spectroscopy experiments on population
imbalanced Fermi gases, which show satisfactory agreement between theory and
experiment for the moderately polarized gases. At high imbalance, experiments
report a paired but normal state at very high and very low T, for both of which
we find no natural theoretical explanation. Given the importance of these
experimental claims, we present a series of related theoretical RF
spectroscopic calculations. By comparison with present and future experiments,
these may help to rule out different scenarios for this strange phase.
\\ ( , 34kb)
Date: Wed, 18 Jul 2007 12:43:57 GMT (303kb)

Title: Condensation of Ideal Bose Gas Confined in a Box within Canonical
Authors: Konstantin Glaum, Hagen Kleinert, Axel Pelster
Categories: cond-mat.stat-mech
Comments: 18 pages, 8 figures
   We set up recursion relations for the partition function and the ground-state
occupancy for a fixed number of non-interacting bosons confined in a square box
potential and determine the temperature dependence of the specific heat and the
particle number in the ground state. A proper semiclassical treatment is set up
which yields the correct small-T-behavior in contrast to an earlier theory in
Feynman's textbook on Statistical Mechanics, in which the special role of the
ground state was ignored. The results are compared with an exact quantum
mechanical treatment. Furthermore, we derive the finite-size effect of the
\\ ( , 303kb)
Date: Thu, 19 Jul 2007 09:38:20 GMT (39kb)

Title: Soliton oscillations in collisionally inhomogeneous attractive
   Bose-Einstein condensates
Authors: P. Niarchou, G. Theocharis, P.G. Kevrekidis, P. Schmelcher, and D.J.
Categories: cond-mat.other
   We investigate bright matter-wave solitons in the presence of a spatially
varying nonlinearity. It is demonstrated that a translation mode is excited due
to the spatial inhomogeneity and its frequency is derived analytically and also
studied numerically. Both cases of purely one-dimensional and ``cigar-shaped''
condensates are studied by means of different mean-field models, and the
oscillation frequencies of the pertinent solitons are found and compared with
the results obtained by the linear stability analysis.Numerical results are
shown to be in very good agreement with the corresponding analytical
\\ ( , 39kb)
Date: Thu, 19 Jul 2007 14:58:57 GMT (414kb)

Title: Localization of Bogolyubov Quasiparticles in Interacting Bose-Einstein
   Condensates Subjected to Correlated Random Potentials
Authors: Pierre Lugan (LCFIO), David Cl\'ement (LCFIO), Philippe Bouyer
   (LCFIO), Alain Aspect (LCFIO), Laurent Sanchez-Palencia (LCFIO)
Categories: cond-mat.other
Comments: 4 pages, 2 figures
Proxy: ccsd hal-00163902
   We study the Anderson localization of Bogolyubov quasiparticles in an
interacting Bose-Einstein condensate (with healing length \xi) subjected to a
random potential (with finite correlation length \sigma_R). We derive
analytically the Lyapunov exponent as a function of the quasiparticle momentum
k and we study the localization maximum k_{max}. For 1D speckle potentials, we
find that k_{max} is proportional to 1/\xi when \xi is much larger than
\sigma_R while k_{max} is proportional to 1/\sigma_R when \xi is much smaller
than \sigma_R, and that the localization is strongest when \xi is of the order
of \sigma_R. Numerical calculations support our analysis and our estimates
indicate that the localization of the Bogolyubov quasiparticles is accessible
in current experiments with ultracold atoms.
\\ ( , 414kb)
Date: Thu, 19 Jul 2007 16:40:46 GMT (61kb)

Title: Excitation Spectra of Correlated Lattice Bosons in a Confining Trap
Authors: Dmitry L. Kovrizhin (Clarendon Laboratory, University of Oxford) G.
   Venketeswara Pai (Technion) Subhasis Sinha (S.N. Bose National Centre for
   Basic Sciences)
Categories: cond-mat.stat-mech
Comments: 4 pages, 3 figures
   We consider ultracold bosonic atoms in an optical lattice with an external
trapping potential. To study the excitation energies of the resulting
Bose-Hubbard model, we develop a method based on a time-dependent
generalization of the Gutzwiller ansatz. We calculate the excitations of the
homogeneous system both in insulating and superfluid regime, concentrating
particularly on those near the superfluid-Mott insulator boundary. Low-lying
excitation energies in presence of a static harmonic trap are obtained using
this method and compared with the homogeneous case. Further, we explore the
dynamics of the center of mass and the breathing mode in response to
time-dependent perturbations of the trap.
\\ ( , 61kb)
arXiv:0707.2665 (*cross-listing*)
Date: Wed, 18 Jul 2007 08:04:13 GMT (13kb)

Title: Hydrodynamic fluctuations in relativistic superfluids
Authors: Manuel A. Valle
Categories: hep-ph cond-mat.other
Comments: 12 pages, no figures
   The Hamiltonian formulation of superfluids based on noncanonical Poisson
brackets is studied in detail. The assumption that the momentum density is
proportional to the flow of the conserved energy is shown to lead to the
covariant relativistic theory previously suggested by Khalatnikov and Lebedev,
and some potentials in this theory are given explicitly. We discuss
hydrodynamic fluctuations in the presence of dissipative effects and we derive
the corresponding set of hydrodynamic correlation functions. Kubo relations for
the transport coefficients are obtained.
\\ ( , 13kb)
Date: Thu, 19 Jul 2007 16:07:45 GMT (598kb)

Title: Strong saturation absorption imaging of dense clouds of ultracold atoms
Authors: G. Reinaudi, T. Lahaye, Z. Wang, and D. Guery-Odelin
Categories: physics.optics physics.atom-ph
Comments: 3 pages, 2 figures
   We report on a far above saturation absorption imaging technique to
investigate the characteristics of dense packets of ultracold atoms. The
transparency of the cloud is controlled by the incident light intensity as a
result of the non-linear response of the atoms to the probe beam. We detail our
experimental procedure to calibrate the imaging system for reliable
quantitative measurements, and demonstrate the use of this technique to extract
the profile and its spatial extent of an optically thick atomic cloud.
\\ ( , 598kb)


replaced with revised version Fri, 13 Jul 2007 06:30:53 GMT (7kb)

Title: A practical method to estimate the condensate fraction of interacting
   and trapped Bose atoms
Authors: Sang-Hoon Kim
Categories: cond-mat.stat-mech
Comments: 2 pages, 2 figures
replaced with revised version Mon, 16 Jul 2007 07:25:49 GMT (40kb)

Title: First and second sound modes at finite temperature in trapped Fermi
   gases from BCS to BEC
Authors: Yan He, Qijin Chen, Chih-Chun Chien, and K. Levin
Categories: cond-mat.str-el cond-mat.supr-con
Comments: 4 pages, 3 figures, replaced with revised version
\\ ( , 40kb)
replaced with revised version Mon, 16 Jul 2007 13:07:18 GMT (35kb)

Title: Predicting spinor condensate dynamics from simple principles
Authors: M. Moreno-Cardoner, J. Mur-Petit, M. Guilleumas, A. Polls, A. Sanpera,
   and M. Lewenstein
Categories: cond-mat.mes-hall
Comments: 4 pages, 2 figures. v3: matches version appeared in PRL
Journal-ref: Phys. Rev. Lett. 99, 020404 (2007)
DOI: 10.1103/PhysRevLett.99.020404
\\ ( , 35kb)
replaced with revised version Sun, 15 Jul 2007 00:03:56 GMT (269kb)

Title: Simulation and detection of Dirac fermions with cold atoms in an optical
Authors: Shi-Liang Zhu, Baigeng Wang, and L.-M. Duan
Categories: cond-mat.mtrl-sci
Comments: 4 pages; Published version
Journal-ref: Phys. Rev. Lett 98, 260402 (2007)
\\ ( , 269kb)
replaced with revised version Mon, 16 Jul 2007 15:48:35 GMT (8kb)

Title: Vortex mass in a superfluid at low frequencies
Authors: D. J. Thouless and J. R. Anglin
Categories: cond-mat.other
Comments: 4 pages
\\ ( , 8kb)
replaced with revised version Sat, 14 Jul 2007 12:45:35 GMT (309kb)

Title: Addressing individual atoms in optical lattices with standing-wave
   driving fields
Authors: Jaeyoon Cho
Categories: quant-ph
Comments: 4 pages, 3 figures; minor revisions
Journal-ref: Phys. Rev. Lett. 99, 020502 (2007)
\\ ( , 309kb)
replaced with revised version Sat, 14 Jul 2007 02:57:22 GMT (435kb)

Title: Demonstration of a moving guide based atom interferometer for rotation
Authors: Saijun Wu, Edward J. Su, Mara Prentiss
Categories: physics.atom-ph physics.optics
Comments: 4 pages, 4 figures (Major revision with new figures)
\\ ( , 435kb)
replaced with revised version Tue, 17 Jul 2007 08:23:17 GMT (16kb)

Title: Nonclassical rotational inertia for a supersolid under rotation
Authors: Amandine Aftalion, Xavier Blanc, Robert L. Jerrard
Categories: cond-mat.other
\\ ( , 16kb)
replaced with revised version Wed, 18 Jul 2007 17:53:46 GMT (33kb)

Title: The axial breathing mode in rapidly rotating Bose-Einstein condensates
   and uncertainty of the rotation velocity
Authors: Gentaro Watanabe
Categories: cond-mat.mes-hall cond-mat.soft nucl-th
Comments: 5 pages, 2 figures; this paper is related to cond-mat/0506331;
   accepted for publication in Phys. Rev. A Rapid Communications
Report-no: NORDITA-2005-80
\\ ( , 33kb)
replaced with revised version Wed, 18 Jul 2007 18:30:13 GMT (144kb)

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
\\ ( , 144kb)
replaced with revised version Wed, 18 Jul 2007 02:42:42 GMT (186kb)

Title: Short-time quantum correlations in the atom optics kicked rotor
Authors: S.A. Wayper, W. Simpson and M.D. Hoogerland
Categories: quant-ph
Comments: 6 pages, 4 figures
\\ ( , 186kb)
replaced with revised version Thu, 19 Jul 2007 10:06:46 GMT (69kb)

Title: Trapped fermionic clouds distorted from the trap shape due to many-body
Authors: Masudul Haque, H.T.C. Stoof
Categories: cond-mat.mes-hall cond-mat.supr-con
Comments: 4+ pages, 3 figures. Formalism for distorted trapped fermi systems +
   treatment of polarized fermion experiments. Version 2: slightly shortened,
   published version
Journal-ref: Physical Review Letters, 98, 260406 (2007)
\\ ( , 69kb)
replaced with revised version Thu, 19 Jul 2007 16:08:19 GMT (823kb)

Title: Cavity-enhanced superradiant Rayleigh scattering with ultra-cold and
   Bose-Einstein condensed atoms
Authors: Sebastian Slama, Gordon Krenz, Simone Bux, Claus Zimmermann, and
   Philippe W. Courteille
Categories: quant-ph
Comments: 10 pages, 10 figures
Journal-ref: Physical Review A 75, 063620 (2007)
DOI: 10.1103/PhysRevA.75.063620
\\ ( , 823kb)

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
Legal stuff: Unless stated otherwise, this e-mail represents only the
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Received on Tue Jul 31 2007 - 15:50:52 EST

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