[Matts-arxiv] Matt's arXiv selection: week ending 10 July 2009

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Sat, 05 Sep 2009 19:40:53 +1000

Dear subscribers,

Jacopo Sabbatini compiled this week's collection. There are 19 new abstracts
and 4 replacements:

Date: Thu, 2 Jul 2009 21:54:50 GMT (501kb)

Title: Dynamic response of 1D bosons in a trap
Authors: Vitaly N. Golovach, Anna Minguzzi and Leonid I. Glazman
Categories: cond-mat.quant-gas cond-mat.mes-hall
Comments: 24 pages, 11 figures
   We calculate the dynamic structure factor S(q,omega) of a one-dimensional
(1D) interacting Bose gas confined in a harmonic trap. The effective
interaction depends on the strength of the confinement enforcing the 1D motion
of atoms; interaction may be further enhanced by superimposing an optical
lattice on the trap potential. In the compressible state, we find that the
smooth variation of the gas density around the trap center leads to softening
of the singular behavior of S(q,omega) at Lieb-1 mode compared to the behavior
predicted for homogeneous 1D systems. Nevertheless, the density-averaged
response remains a non-analytic function of q and omega at Lieb-1 mode in the
limit of weak trap confinement. The exponent of the power-law non-analyticity
is modified due to the inhomogeneity in a universal way, and thus, bears
unambiguously the information about the (homogeneous) Lieb-Liniger model. A
strong optical lattice causes formation of Mott phases. Deep in the Mott
regime, we predict a semi-circular peak in S(q,\omega) centered at the on-site
repulsion energy, omega=U. Similar peaks of smaller amplitudes exist at
multiples of U as well. We explain the suppression of the dynamic response with
entering into the Mott regime, observed recently by D. Clement et al., Phys.
Rev. Lett. v. 102, p. 155301 (2009), based on an f-sum rule for the
Bose-Hubbard model.
\\ ( http://arxiv.org/abs/0907.0483 , 501kb)
Date: Fri, 3 Jul 2009 08:54:23 GMT (2338kb,D)

Title: Vortex nucleation in mesoscopic Bose superfluid and breaking of the
   parity symmetry
Authors: D. Dagnino, N. Barber\'an, and M. Lewenstein
Categories: cond-mat.quant-gas
Comments: 14 pages, 27 figures
   We analyze vortex nucleation in mezoscopic 2D Bose superfluid in a rotating
trap. We explicitly include a weakly anisotropic stirring potential, breaking
thus explicitly the axial symmetry. As the rotation frequency passes the
critical value $\Omega_c$ the system undergoes an extra symmetry
change/breaking. Well below $\Omega_c$ the ground state is properly described
by the mean field theory with an even condensate wave function. Well above
$\Omega_c$ the MF solution works also well, but the order parameter becomes
odd. This phenomenon involves therefore a discrete parity symmetry breaking. In
the critical region the MF solutions exhibit dynamical instability. The true
many body state is a strongly correlated entangled state involving two
macroscopically occupied modes (eigenstates of the single particle density
operator). We characterize this state in various aspects: i) the eligibility
for adiabatic evolution; ii) its analytical approximation given by the
maximally entangled combination of two single modes; and finally iii) its
appearance in particle detection measurements.
\\ ( http://arxiv.org/abs/0907.0564 , 2338kb)
Date: Fri, 3 Jul 2009 12:46:06 GMT (75kb)

Title: Critical velocity of superfluid flow through single barrier and periodic
Authors: Gentaro Watanabe, F. Dalfovo, F. Piazza, L. P. Pitaevskii, S.
Categories: cond-mat.quant-gas cond-mat.supr-con
Comments: 10 pages, 6 figures
   We investigate the problem of an ultracold atomic gas in the superfluid phase
flowing in the presence of a potential barrier or a periodic potential. We use
a hydrodynamic scheme in the local density approximation (LDA) to obtain an
analytic expression for the critical current as a function of the barrier
height or the lattice intensity, which applies to both Bose and Fermi
superfluids. In this scheme, the stationary flow becomes energetically unstable
when the local superfluid velocity is equal to the local sound velocity at the
point where the external potential is maximum. We compare this prediction with
the results of the numerical solutions of the Gross-Pitaevskii and
Bogoliubov-de Gennes equations. We discuss the role of long wavelength
excitations in determining the critical velocity. Our results allow one to
identify the different regimes of superfluid flow, namely, the LDA hydrodynamic
regime, the regime of quantum effects beyond LDA for weak barriers and the
regime of tunnelling between weakly coupled superfluids for strong barriers. We
finally discuss the relevance of these results in the context of current
experiments with ultracold gases.
\\ ( http://arxiv.org/abs/0907.0621 , 75kb)
Date: Fri, 3 Jul 2009 12:59:56 GMT (769kb)

Title: Dark solitons near the Mott-insulator--superfluid phase transition
Authors: K.V.Krutitsky, J.Larson, M.Lewenstein
Categories: cond-mat.quant-gas
   Dark solitons of ultracold bosons in the vicinity of the
Mott-insulator--superfluid phase transition are studied. Making use of the
Gutzwiller ansatz we have found antisymmetric eigenstates corresponding to
standing solitons, as well as propagating solitons created by phase imprinting.
The properties of both types of solitons are studies and in particular it is
demonstrate that quantum fluctuations greatly affect the characteristics of the
\\ ( http://arxiv.org/abs/0907.0625 , 769kb)
Date: Fri, 3 Jul 2009 15:06:06 GMT (244kb)

Title: Antiferromagnetic noise correlations in optical lattices
Authors: G. M. Bruun, O. F. Syljuasen, K. G. L. Pedersen, B. M. Andersen, E.
   Demler, A. S. Sorensen
Categories: cond-mat.quant-gas
Comments: 4 pages, 4 figures
   We analyze how noise correlations probed by time-of-flight (TOF) experiments
reveal antiferromagnetic (AF) correlations of fermionic atoms in
two-dimensional (2D) and three-dimensional (3D) optical lattices. Combining
analytical and quantum Monte Carlo (QMC) calculations using experimentally
realistic parameters, we show that AF correlations can be detected for
temperatures above and below the critical temperature for AF ordering. It is
demonstrated that spin-resolved noise correlations yield important information
about the spin ordering. Finally, we show how to extract the spin correlation
length and the related critical exponent of the AF transition from the noise.
\\ ( http://arxiv.org/abs/0907.0652 , 244kb)
Date: Fri, 3 Jul 2009 17:11:31 GMT (644kb)

Title: Single-atom-sensitive fluorescence imaging of ultracold quantum gases
Authors: R. B\"ucker, A. Perrin, S. Manz, T. Betz, Ch. Koller, T. Plisson, J.
   Rottmann, T. Schumm, and J. Schmiedmayer
Categories: physics.atom-ph
Comments: 23 pages, 10 figures
   We present a novel imaging system for ultracold quantum gases in expansion.
After release from a confining potential, atoms fall through a sheet of
resonant excitation laser light and the emitted fluorescence photons are imaged
onto an amplified CCD camera using a high numerical aperture optical system.
The imaging system reaches an extraordinary dynamic range, not attainable with
conventional absorption imaging. We demonstrate single-atom detection for
dilute atomic clouds with high efficiency where at the same time dense
Bose-Einstein condensates can be imaged without saturation or distortion. The
spatial resolution can reach the sampling limit as given by the 8 microns pixel
size in object space. Pulsed operation of the detector allows for slice images
and hence a 3D tomography of the measured object. The scheme can easily be
implemented for any atomic species and all optical components are situated
outside the vacuum system. As a first application we perform thermometry on
rubidium Bose-Einstein condensates created on an atom chip.
\\ ( http://arxiv.org/abs/0907.0674 , 644kb)
Date: Fri, 3 Jul 2009 21:14:51 GMT (38kb)

Title: Semiclassical dynamics of atomic Bose-Einstein condensates
Authors: S. Choi and B. Sundaram
Categories: cond-mat.quant-gas
Comments: 4 figures. Submitted for publication
   An atomic Bose-Einstein condensate (BEC) is often described as a macroscopic
object which can be approximated by a coherent state. This, on the surface,
would appear to indicate that its behavior should be close to being classical.
In this paper, we clarify the extent of how ``classical'' a BEC is by exploring
the semiclassical equations for BECs under the mean field Gaussian
approximation. Such equations describe the dynamics of a condensate in the
classical limit in terms of the variables < x > and < p > as well as their
respective variances. We compare the semiclassical solution with the full
quantum solution based on the Gross-Pitaevskii Equation (GPE) and find that the
interatomic interactions which generate nonlinearity make the system less
``classical.'' On the other hand, many qualitative features are captured by the
semiclassical equations, and the equations to be solved are far less
computationally intensive than solving the GPE which make them ideal for
providing quick diagnostics, and for obtaining new intuitive insight.
\\ ( http://arxiv.org/abs/0907.0720 , 38kb)
Date: Mon, 6 Jul 2009 15:52:48 GMT (133kb)

Title: Coherence time of a Bose-Einstein condensate
Authors: Alice Sinatra (LKB - Lhomond), Yvan Castin (LKB - Lhomond), Emilia
Categories: cond-mat.quant-gas
Comments: 17 pages, 8 figures
   Temporal coherence is a fundamental property of macroscopic quantum systems,
such as lasers in optics and Bose-Einstein condensates in atomic gases and it
is a crucial issue for interferometry applications with light or matter waves.
Whereas the laser is an "open" quantum system, ultracold atomic gases are
weakly coupled to the environment and may be considered as isolated. The
coherence time of a condensate is then intrinsic to the system and its
derivation is out of the frame of laser theory. Using quantum kinetic theory,
we predict that the interaction with non-condensed modes gradually smears out
the condensate phase, with a variance growing as A t^2+B t+C at long times t,
and we give a quantitative prediction for A, B and C. Whereas the coefficient A
vanishes for vanishing energy fluctuations in the initial state, the
coefficients B and C are remarkably insensitive to these fluctuations. The
coefficient B describes a diffusive motion of the condensate phase that sets
the ultimate limit to the condensate coherence time. We briefly discuss the
possibility to observe the predicted phase spreading, also including the effect
of particle losses.
\\ ( http://arxiv.org/abs/0907.1025 , 133kb)
Date: Mon, 6 Jul 2009 20:23:22 GMT (106kb)

Title: Two-dimensional boson-fermion mixtures
Authors: A. L. Subasi, S. Sevincli, P. Vignolo, B. Tanatar
Categories: cond-mat.quant-gas
Comments: 9 pages, 4 figures
Journal-ref: Phys. Rev. A 79, 063632 (2009)
DOI: 10.1103/PhysRevA.79.063632
   Using mean-field theory, we study the equilibrium properties of boson-fermion
mixtures confined in a harmonic pancake-shaped trap at zero temperature. When
the modulus of the s-wave scattering lengths are comparable to the mixture
thickness, two-dimensional scattering events introduce a logarithmic dependence
on density in the coupling constants, greatly modifying the density profiles
themselves. We show that for the case of a negative boson-fermion
three-dimensional s-wave scattering length, the dimensional crossover
stabilizes the mixture against collapse and drives it towards spatial demixing.
\\ ( http://arxiv.org/abs/0907.1096 , 106kb)
Date: Tue, 7 Jul 2009 12:33:10 GMT (60kb)

Title: Probing the quantum ground state of a spin-1 Bose-Einstein condensate
   with cavity transmission spectra
Authors: J. M. Zhang, S. Cui, H. Jing, D. L. Zhou, and W. M. Liu
Categories: cond-mat.quant-gas quant-ph
Comments: 6 pages, 1 figure
   We propose to probe the quantum ground state of a spin-1 Bose-Einstein
condensate with the transmission spectra of an optical cavity. By choosing a
circularly polarized cavity mode with an appropriate frequency, we can realize
coupling between the cavity mode and the magnetization of the condensate. The
cavity transmission spectra then contain information of the magnetization
statistics of the condensate and thus can be used to distinguish the
ferromagnetic and antiferromagnetic quantum ground states. This technique may
also be useful for continuous observation of the spin dynamics of a spinor
Bose-Einstein condensate.
\\ ( http://arxiv.org/abs/0907.1200 , 60kb)
Date: Tue, 7 Jul 2009 16:10:16 GMT (86kb)

Title: Generalized nonpolynomial Schrodinger equations for matter waves under
   anisotropic transverse confinement
Authors: Luca Salasnich
Categories: cond-mat.quant-gas
Comments: 9 pages, 2 figures, to be published in Journal of Physics A: Math.
   Starting from the three-dimensional Gross-Pitaevskii equation we derive a 1D
generalized nonpolynomial Schrodinger equation, which describes the dynamics of
Bose-Einstein condensates under the action of a generic potential in the
longitudinal axial direction and of an anisotropic harmonic potential in the
transverse radial direction. This equation reduces to the familiar 1D
nonpolynomial Schrodinger equation [Phys. Rev. A 65, 043614 (2002)] in the case
of isotropic transverse harmonic confinement. In addition, we show that if the
longitudinal potential models a periodic optical lattice the 3D GPE can be
mapped into a 1D generalized discrete nonpolynomial Schrodinger equation.
\\ ( http://arxiv.org/abs/0907.1248 , 86kb)
Date: Tue, 7 Jul 2009 17:01:06 GMT (164kb)

Title: Supersolid and solitonic phases in one-dimensional Extended Bose-Hubbard
Authors: Tapan Mishra, Ramesh V. Pai, S. Ramanan, Meetu Sethi Luthra and B. P.
Categories: cond-mat.quant-gas cond-mat.other
Comments: 7 pages, 11 figures
   We report our findings on quantum phase transitions in cold bosonic atoms in
a one dimensional optical lattice using the finite size density matrix
renormalization group method in the framework of the extended Bose-Hubbard
model. We consider wide ranges of values for the filling factors and the
nearest neighbor interactions. At commensurate fillings, we obtain two
different types of charge density wave phases and a Mott insulator phase.
However, departure from commensurate fillings yield the exotic supersolid phase
where both the crystalline and the superfluid orders coexist. In addition, we
obtain signatures for solitary waves and also superfluidity.
\\ ( http://arxiv.org/abs/0907.1258 , 164kb)
Date: Wed, 8 Jul 2009 01:33:30 GMT (818kb,D)

Title: Versatile transporter apparatus for experiments with optically trapped
   Bose-Einstein condensates
Authors: Daniel Pertot, Daniel Greif, Stephan Albert, Bryce Gadway, Dominik
Categories: cond-mat.quant-gas
   We describe a versatile and simple scheme for producing magnetically and
optically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil
transporter apparatus. The apparatus features a TOP trap that incorporates the
movable quadrupole coils used for magneto-optical trapping and long-distance
magnetic transport of atomic clouds. As a stand-alone device, this trap allows
for the stable production of condensates containing up to one million atoms. In
combination with an optical dipole trap, the TOP trap acts as a funnel for
efficient loading, after which the quadrupole coils can be retracted, thereby
maximizing optical access. The robustness of this scheme is illustrated by
realizing the superfluid-to-Mott insulator transition in a three-dimensional
optical lattice.
\\ ( http://arxiv.org/abs/0907.1323 , 818kb)
Date: Wed, 8 Jul 2009 03:11:59 GMT (1458kb)

Title: Many-body physics in the radio frequency spectrum of lattice bosons
Authors: Kaden R. A. Hazzard, Erich J. Mueller (Cornell)
Categories: cond-mat.quant-gas
Comments: 6 pages, 4 figures, 13 subfigures
   We calculate the radio-frequency spectrum of a trapped cloud of cold bosonic
atoms in an optical lattice. Using random phase and local density
approximations we produce both trap averaged and spatially resolved spectra,
identifying simple features in the spectra that reveal information about both
superfluidity and correlations. Our approach is exact in the deep Mott limit
and in the deep superfluid when the hopping rates for the two internal spin
states are equal. It contains final state interactions, obeys the Ward
identities (and the associated conservation laws), and satisfies the $f$-sum
rule. Motivated by earlier work by Sun, Lannert, and Vishveshwara [Phys. Rev. A
\textbf{79}, 043422 (2009)], we also discuss the features which arise in a
spin-dependent optical lattice.
\\ ( http://arxiv.org/abs/0907.1332 , 1458kb)
Date: Thu, 9 Jul 2009 19:50:30 GMT (296kb)

Title: Ferro-Nematic ground state of the dilute dipolar Fermi gas
Authors: Benjamin M. Fregoso and Eduardo Fradkin
Categories: cond-mat.quant-gas cond-mat.str-el
Comments: 4 pages, 3 figures; minor misprints corrected
   We show using a ``Thomas-Fermi'' variational wave function with a
distribution function in momentum space, that a homogeneous two-component Fermi
gas with dipolar interactions has a ferro-nematic ground state for non-zero
(arbitrarily small) values of the dipolar coupling constant. The ferro-nematic
phase is characterized by having a non-zero magnetization and long range
orientational uniaxial order. The Fermi surface of spin up (down) component is
elongated (compressed) along the direction of the magnetization. We calculate
several thermodynamic quantities and discuss the prospects of experimental
\\ ( http://arxiv.org/abs/0907.1345 , 296kb)
Date: Wed, 8 Jul 2009 10:30:11 GMT (115kb)

Title: Phase diagrams of the Bose-Hubbard model at finite temperature
Authors: I.V. Stasyuk and T.S. Mysakovych
Categories: cond-mat.other
   The phase transitions in the Bose-Hubbard model are investigated. A
single-particle Green's function is calculated in the random phase
approximation and the formalism of the Hubbard operators is used. The regions
of existence of the superfluid and Mott insulator phases are established and
the $(\mu,t)$ (the chemical potential -- transfer parameter) phase diagrams are
built. The influence of temperature change on this transition is analyzed and
the phase diagram in the $(T,\mu)$ plane is constructed. The role of thermal
activation of the ion hopping is investigated by taking into account the
temperature dependence of the transfer parameter. The reconstruction of the
Mott-insulator lobes due to this effect is analyzed.
\\ ( http://arxiv.org/abs/0907.1382 , 115kb)
Date: Thu, 9 Jul 2009 13:13:49 GMT (200kb)

Title: Luttinger liquid of trimers in Fermi gases with unequal masses
Authors: Giuliano Orso, Evgeni Burovski, and Thierry Jolicoeur
Categories: cond-mat.quant-gas cond-mat.supr-con
Comments: 4+ pages,4 figures
   We investigate one dimensional attractive Fermi gases in spin-dependent
optical lattices. Starting from the asymmetric Hubbard model, we show that
three-body bound states - ``trimers'' - exist as soon as the two tunneling
rates are different. We calculate the binding energy and the effective mass of
a single trimer. We then show numerically that for finite commensurate
densities $n_\uparrow=n_\downarrow/2$ an energy gap appears, implying that the
gas is a one-component Luttinger liquid of trimers with suppressed superfluid
ordering. The boundaries of this exotic phase are given.
\\ ( http://arxiv.org/abs/0907.1533 , 200kb)
Date: Thu, 9 Jul 2009 15:26:55 GMT (161kb)

Title: Observation of stable 3-vortex/anti-vortex clusters in a superfluid
   Bose-Einstein condensate
Authors: J. A. Seman, E. A. L. Henn, R. F. Shiozaki, E. R. F. Ramos, M.
   Caracanhas, C. Castelo Branco, G. Roati, M. Haque, K. M. F. Magalh\~aes and
   V. S. Bagnato
Categories: cond-mat.quant-gas
Comments: 4 pages, 4 figures
   We report on the observation of stable configurations of clusters with three
vortices in a Rb87 Bose-Einstein condensate. We observe preferentially two
types of 3-vortex/anti-vortex configurations. Vortices are either distributed
as an equilateral triangle or as a liner array. The results are consistent with
the theory where the triangular configuration is formed by vortices with the
same circulation sign, while, in contrast, the linear array is constituted of a
central vortex with a sign of circulation opposite to the side ones.
\\ ( http://arxiv.org/abs/0907.1584 , 161kb)
Date: Wed, 8 Jul 2009 03:48:44 GMT (672kb)

Title: Demonstrating mesoscopic superpositions in double-well Bose-Einstein
Authors: T.J. Haigh, A.J. Ferris, M.K. Olsen
Categories: quant-ph
Comments: 14 pages, 8 figures
   The availability of Bose-Einstein condensates as mesoscopic or macroscopic
quantum objects has aroused new interest in the possiblity of making and
detecting coherent superpositions involving many atoms. In this article we show
that it may be possible to generate such a superposition state in a reasonably
short time using Feshbach resonances to tune the inter-atomic interactions in a
double-well condensate.
   We also consider the important problem of distinguishing whether a coherent
superposition or a statistical mixture is generated by a given experimental
procedure. We find that unambiguously distinguishing even a perfect `NOON'
state from a statistical mixture using standard detection methods will present
experimental difficulties.
\\ ( http://arxiv.org/abs/0907.1333 , 672kb)

The replacements:

replaced with revised version Fri, 3 Jul 2009 13:22:24 GMT (1609kb)

Title: A method to create disordered vortex arrays in atomic Bose-Einstein
Authors: Eniko J. M. Madarassy
Categories: cond-mat.other
Comments: 17 pages, 12 figures. Accepted by the Canadian Journal of Physics
\\ ( http://arxiv.org/abs/0808.0636 , 1609kb)
replaced with revised version Mon, 6 Jul 2009 09:39:42 GMT (388kb)

Title: The Stochastic Gross-Pitaevskii Equation and some Applications
Authors: S. P. Cockburn, N. P. Proukakis
Categories: cond-mat.other
Comments: 14 pages, 9 figures. Corrected typos
Journal-ref: Laser Physics, 2009, Vol. 19, No. 4 (Special Issue on Physics of
   Cold Trapped Atoms)
\\ ( http://arxiv.org/abs/0812.1926 , 388kb)
replaced with revised version Sun, 5 Jul 2009 09:37:23 GMT (29kb,D)

Title: Rigorous Upper Bound on the Critical Temperature of Dilute Bose Gases
Authors: Robert Seiringer, Daniel Ueltschi
Categories: cond-mat.stat-mech cond-mat.quant-gas math-ph math.MP
Comments: 10 pages, 2 figures
Journal-ref: Phys. Rev. B 80, 014502 (2009)
DOI: 10.1103/PhysRevB.80.014502
\\ ( http://arxiv.org/abs/0904.0050 , 29kb)
replaced with revised version Thu, 9 Jul 2009 18:29:39 GMT (3891kb)

Title: Feshbach Resonances in Ultracold Gases
Authors: Cheng Chin, Rudolf Grimm, Paul Julienne, and Eite Tiesinga
Categories: cond-mat.other
Comments: Review article, 63 pages, 48 figures
\\ ( http://arxiv.org/abs/0812.1496 , 3891kb)

Till next time,

Dr M. J. Davis,                      Associate Professor in Physics
School of Mathematics and Physics,   ph  : +61 7 334 69824
The University of Queensland,        fax : +61 7 336 51242
Brisbane, QLD 4072,                  mdavis_at_physics.uq.edu.au
Australia.                           www.physics.uq.edu.au/people/mdavis/
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