[Matts-arxiv] Matt's arXiv selection: week ending 21 August 2009.

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Sun, 20 Sep 2009 10:16:46 +1000

Dear subscribers,

Jacopo Sabbatini compiled this week's abstracts. There are 13 new preprints and
  7 replacements.

Date: Fri, 14 Aug 2009 14:35:15 GMT (157kb)

Title: Strongly interacting trapped bosons yield fragmented transverse states
   in the crossover to low dimension
Authors: Uwe R. Fischer and Philipp Bader
Categories: cond-mat.quant-gas
Comments: 5 pages of RevTex4, 3 figures
   We investigate trapped bosonic gases approaching the crossover to lower
dimension from the coherent (Bose-Einstein condensate) side, along the
transverse confining direction. Using a variational analysis, we derive the
fragmentation of the Bose-Einstein condensate into two mutually incoherent
macroscopically occupied field operator modes, upon increasing a dimensionless
interaction measure beyond a critical value.
\\ ( http://arxiv.org/abs/0908.2026 , 157kb)
Date: Fri, 14 Aug 2009 14:12:38 GMT (76kb,D)

Title: Search for broad Feshbach resonances in the 6Li-40K mixture
Authors: T.G. Tiecke, M.R. Goosen, A. Ludewig, S.D. Gensemer, S. Kraft,
   S.J.J.M.F. Kokkelmans, and J.T.M. Walraven
Categories: cond-mat.quant-gas
Comments: 4 pages, 2 figures
   We explore the widths of interspecies Feshbach resonances in a mixture of the
fermionic quantum gases 6Li and 40K. Experimentally, we obtain the asymmetric
lineshape of the interspecies elastic cross section by measuring the
distillation rate of 6Li atoms from an optically-trapped 6Li-40K mixture as a
function of magnetic field. This provides us with the first experimental
determination of the width of a resonance in this mixture, Delta B=1.5(5) G,
being one of the broadest. We present an extended version of the Asymptotic
Bound-state Model (ABM) and show that this model offers a convenient method to
estimate the width and position of a large number of Feshbach resonances. Our
results offer good perspectives for the observation of universal crossover
physics in this mixture.
\\ ( http://arxiv.org/abs/0908.2071 , 76kb)
Date: Fri, 14 Aug 2009 06:43:18 GMT (324kb)

Title: Quantum interference in the time-of-flight distribution
Authors: Md. Manirul Ali and Hsi-Sheng Goan
Categories: quant-ph
Comments: 5 figures, Accepted by Journal of Physics A: Mathematical and
   We propose a scheme to experimentally observe matter-wave interference in the
time domain, specifically in the arrival-time or the time-of-flight (TOF)
distribution for atomic BEC Schrodinger-cat state represented by superposition
of macroscopically separated wave packets in space. This is in contrast to
interference in space at a fixed time observed in reported BEC experiments. We
predict and quantify the quantum interference in the TOF distribution
calculated from the modulus of the quantum probability current density (rather
than the TOF distributions obtained from a purely classical or semi-classical
treatment in many reported experiments). The interference and hence the
coherence in the quantum TOF signal disappears in the large-mass limit. Our
scheme has the potential to probe the validity of various other theoretical
approaches (Phys. Rep. 338, 353 (2000)) of calculating the quantum arrival time
\\ ( http://arxiv.org/abs/0908.2018 , 324kb)
Date: Sat, 15 Aug 2009 04:25:43 GMT (25kb)

Title: Universal Four-Component Fermi Gas in One Dimension
Authors: Yusuke Nishida and Dam T. Son
Categories: cond-mat.quant-gas
Comments: 4 pages, 1 figure
Report-no: MIT-CTP 4055, INT-PUB-09-038
   A four-component Fermi gas in one dimension with a short-range four-body
interaction is shown to exhibit a one-dimensional analog of the BCS-BEC
crossover. Its low-energy physics is governed by a Tomonaga-Luttinger liquid
with three spin gaps. The spin gaps are exponentially small in the weak
coupling limit when it is due to the BCS-like pairing, while they are large in
the strong coupling ("BEC") limit because of the formation of tightly-bound
tetramers. We investigate the sound velocity and the gap spectrum in the
BCS-BEC crossover. Exact relationships valid in our system are also discussed.
\\ ( http://arxiv.org/abs/0908.2159 , 25kb)
Date: Mon, 17 Aug 2009 07:04:34 GMT (1881kb)

Title: Vortex structures in rotating Bose-Einstein condensates
Authors: S. I. Matveenko, D. Kovrizhin, S. Ouvry, G. V. Shlyapnikov
Categories: cond-mat.quant-gas cond-mat.stat-mech
Comments: 15 pages, 9 figures
   We present an analytical solution for the vortex lattice in a rapidly
rotating trapped Bose-Einstein condensate (BEC) in the lowest Landau level and
discuss deviations from the Thomas-Fermi density profile. This solution is
exact in the limit of a large number of vortices and is obtained for the cases
of circularly symmetric and narrow channel geometries. The latter is realized
when the trapping frequencies in the plane perpendicular to the rotation axis
are different from each other and the rotation frequency is equal to the
smallest of them. This leads to the cancelation of the trapping potential in
the direction of the weaker confinement and makes the system infinitely
elongated in this direction. For this case we calculate the phase diagram as a
function of the interaction strength and rotation frequency and identify the
order of quantum phase transitions between the states with a different number
of vortex rows.
\\ ( http://arxiv.org/abs/0908.2172 , 1881kb)
Date: Mon, 17 Aug 2009 11:02:54 GMT (11kb)

Title: Particle fluctuations in nonuniform and trapped Bose gases
Authors: V.I. Yukalov
Categories: cond-mat.quant-gas cond-mat.stat-mech
Comments: Latex file, 16 pages
Journal-ref: Laser Phys. Lett. 6 (2009) 688-695
   The problem of particle fluctuations in arbitrary nonuniform systems with
Bose-Einstein condensate is considered. This includes the case of trapped Bose
atoms. It is shown that the correct description of particle fluctuations for
any nonuniform system of interacting atoms always results in thermodynamically
normal fluctuations.
\\ ( http://arxiv.org/abs/0908.2323 , 11kb)
Date: Tue, 18 Aug 2009 02:09:05 GMT (111kb)

Title: Quarter-filled supersolid and solid phases in the extended Bose-Hubbard
Authors: Kwai-Kong Ng, Y.C. Chen, Y.C. Tzeng
Categories: cond-mat.other
Comments: 6 pages, 9 figures
   We numerically study the ground state phase diagram of the two-dimensional
hard-core Bose-Hubbard model with nearest ($V_1$) and next nearest neighbor
($V_2$) repulsions. In particular, we focus on the quarter-filled phases where
one supersolid and two solid phases are observed. Using both canonical and
grand canonical quantum Monte Carlo (QMC) methods and a mean field calculation,
we confirm the existence of a \textit{commensurate} supersolid at quarter boson
filling. The nature of the commensurate supersolid will be discussed. Only one
kind of the supersolid phase is found energetically stable despite of the two
possible diagonal long range orderings for the solid phase. The competition
between the two solid phases manifests as a first order phase transition around
$2 V_2\sim V_1$. The change of order parameters as functions of the chemical
function is also presented.
\\ ( http://arxiv.org/abs/0908.2478 , 111kb)
Date: Tue, 18 Aug 2009 12:39:19 GMT (908kb)

Title: Time-dependent currents of 1D bosons in an optical lattice
Authors: Johannes Schachenmayer, Guido Pupillo and Andrew J. Daley
Categories: cond-mat.quant-gas
Comments: 18 pages, 10 figures, submitted to New J. Phys
   We analyse the time-dependence of currents in a 1D Bose gas in an optical
lattice. For a 1D system, the stability of currents induced by accelerating the
lattice exhibits a broad crossover as a function of the magnitude of the
acceleration, and the strength of the inter-particle interactions. This differs
markedly from mean-field results in higher dimensions. Using the infinite Time
Evolving Block Decimation algorithm, we characterise this crossover by making
quantitative predictions for the time-dependent behaviour of the currents and
their decay rate. We also compute the time-dependence of quasi-condensate
fractions which can be measured directly in experiments. We compare our results
to calculations based on phase-slip methods, finding agreement with the scaling
as the particle density increases, but with significant deviations near unit
\\ ( http://arxiv.org/abs/0908.2485 , 908kb)
Date: Tue, 18 Aug 2009 12:15:36 GMT (789kb,D)

Title: Finite temperature dynamics of a single vortex in a Bose-Einstein
   condensate: Equilibrium precession and rotational symmetry breaking
Authors: T. M. Wright, A. S. Bradley, R. J. Ballagh,
Categories: cond-mat.quant-gas
Comments: 21 pages, 10 figures
   We consider a finite temperature Bose-Einstein condensate in a quasi-2D trap
containing a single precessing vortex. We find that such a configuration arises
naturally as an ergodic equilibrium of the projected Gross-Pitaevskii equation,
when constrained to a finite conserved angular momentum. In an isotropic
trapping potential the condensation of the classical field into an off-axis
vortex state breaks the rotational symmetry of the system. We present a
methodology to identify the condensate and the Goldstone mode associated with
the broken rotational symmetry in the classical-field model. We also examine
the variation in vortex trajectories and thermodynamic parameters of the field
as the energy of the microcanonical field simulation is varied.
\\ ( http://arxiv.org/abs/0908.2551 , 789kb)
Date: Wed, 19 Aug 2009 16:16:50 GMT (135kb)

Title: The spin evolution of spin-3 $^{52}$Cr Bose-Einstein condensate
Authors: Yanzhang He
Categories: cond-mat.quant-gas cond-mat.other
Comments: 5 pages, 3 figures
   The spin evolution of a Bose-Einstein condensate starting from a mixture of
two or three groups of $^{52}$Cr (spin-3) atoms in an optical trap has been
studied theoretically. The initial state is so chosen that the system does not
distinguish up and down. In this choice, the deviation caused by the
single-mode approximation is reduced. Moreover, since the particle number is
given very small (N=20), the deviation caused by the neglect of the long-range
dipole force is also reduced. Making use of these two simplifications, a
theoretical calculation beyond the mean field theory is performed. The
numerical results are help to evaluate the unknown strength $g_0$.
\\ ( http://arxiv.org/abs/0908.2781 , 135kb)
Date: Wed, 19 Aug 2009 17:59:01 GMT (202kb)

Title: Dynamical quantum phase transition of a two-component Bose-Einstein
   condensate in an optical lattice
Authors: Anssi Collin, Jani-Petri Martikainen, Jonas Larson
Categories: cond-mat.quant-gas cond-mat.other
Comments: 8 pages, 8 figures
   We study dynamics of a two-component Bose-Einstein condensate where the two
components are coupled via an optical lattice. In particular, we focus on the
dynamics as one drives the system through a critical point of a first order
phase transition characterized by a jump in the internal populations. Solving
the time-dependent Gross-Pitaevskii equation, we analyze; breakdown of
adiabaticity, impact of non-linear atom-atom scattering, and the role of a
harmonic trapping potential. Our findings demonstrate that the phase transition
is resilient to both contact interaction between atoms and external trapping
\\ ( http://arxiv.org/abs/0908.2792 , 202kb)
Date: Thu, 20 Aug 2009 14:23:37 GMT (112kb)

Title: The dynamics of coherence between coupled and decoupled one-dimensional
Authors: R.G. Scott and D.A.W. Hutchinson
Categories: cond-mat.quant-gas
   We reproduce the sub-exponential decoherence of one-dimensional
quasicondensates observed in recent experiments. Counter-intuitively, the
quasicondensates may decohere even when stongly coupled, if the temperature is
large enough or the peak density is low enough to allow significant density
fluctuations. We also propose an experiment to investigate the growth of
coherence between two initially incoherent quasicondensates. We predict that
the coherence will rise on a much slower timescale, and the final coherence
again depends strongly on the density fluctuations.
\\ ( http://arxiv.org/abs/0908.2930 , 112kb)
Date: Thu, 20 Aug 2009 18:42:44 GMT (1445kb,D)

Title: Classical versus quantum dynamics of the atomic Josephson junction
Authors: G.J. Krahn and D.H.J. O'Dell
Categories: cond-mat.quant-gas
Comments: 31 pages, 14 figures
   We compare the classical (mean-field) dynamics with the quantum dynamics of
atomic Bose-Einstein condensates in double-well potentials. The quantum
dynamics are computed using a simple scheme based upon the Raman-Nath
equations. Two different methods for exciting a non-equilbrium state are
considered: an asymmetry between the wells which is suddenly removed, and a
periodic time oscillating asymmetry. The first method generates wave packets
that lead to collapses and revivals of the expectation values of the
macroscopic variables, and we calculate the time scale for these revivals. The
second method permits the excitation of a single energy eigenstate of the
many-particle system, including Schroedinger cat states. We also discuss a band
theory interpretation of the energy level structure of an asymmetric
double-well, thereby identifying analogies to Bloch oscillations and Bragg
resonances. Both the Bloch and Bragg dynamics are purely quantum and are not
contained in the mean-field treatment.
\\ ( http://arxiv.org/abs/0908.2976 , 1445kb)

The replacements:

replaced with revised version Mon, 17 Aug 2009 07:18:18 GMT (756kb)

Title: Hopping modulation in a one-dimensional Fermi-Hubbard Hamiltonian
Authors: F. Massel, M. J. Leskinen, P. Torma
Categories: cond-mat.quant-gas
Comments: 4 pages, 5 figures; minor changes in the text, updated references;
Journal-ref: Phys. Rev. Lett. 103, 066404 (2009)
\\ ( http://arxiv.org/abs/0904.4815 , 756kb)
replaced with revised version Sun, 16 Aug 2009 18:02:57 GMT (891kb)

Title: Systematic reduction of sign errors in many-body problems:
   generalization of self-healing diffusion Monte Carlo to excited states
Authors: Fernando A. Reboredo
Categories: cond-mat.str-el cond-mat.quant-gas
Comments: New version with two new figures. Several formulas of intermediate
   steps in the analytical derivations have been added. The review reports and
   replies with a summary of changes are included in the source pdf files with
   nicer figures are also included in the source
\\ ( http://arxiv.org/abs/0906.4359 , 891kb)
replaced with revised version Sat, 15 Aug 2009 09:47:58 GMT (137kb)

Title: Ground state of a tightly bound composite dimer immersed in a Fermi Sea
Authors: Christophe Mora (LPA), Fr\'ed\'eric Chevy (LKB - Lhomond)
Categories: cond-mat.quant-gas
Comments: 11 pages; 3 figures
\\ ( http://arxiv.org/abs/0908.0608 , 137kb)
replaced with revised version Sun, 16 Aug 2009 21:39:46 GMT (202kb)

Title: Sign of tunnel coupling in barrier-separated Bose-Einstein condensates
   and stability of double-ring systems
Authors: Joachim Brand, Tania J. Haigh, and Ulrich Z\"ulicke
Categories: quant-ph
Comments: 4 pages, comment on Phys. Rev. Lett. 98, 050401 (2007)
\\ ( http://arxiv.org/abs/0805.4447 , 202kb)
replaced with revised version Mon, 17 Aug 2009 12:32:38 GMT (76kb)

Title: Independent Control of Scattering Lengths in Multicomponent Quantum
Authors: Peng Zhang, Pascal Naidon and Masahito Ueda
Categories: physics.atom-ph cond-mat.other quant-ph
Comments: 4pages, 3figures
\\ ( http://arxiv.org/abs/0901.0694 , 76kb)
replaced with revised version Mon, 17 Aug 2009 11:52:39 GMT (71kb)

Title: Dynamics of an inhomogeneous quantum phase transition
Authors: Jacek Dziarmaga and Marek M. Rams
Categories: quant-ph cond-mat.mes-hall cond-mat.quant-gas cond-mat.stat-mech
Comments: 7 pages, 4 figures; longer version with improved presentation;
\\ ( http://arxiv.org/abs/0904.0115 , 71kb)
replaced with revised version Mon, 17 Aug 2009 02:56:40 GMT (114kb)

Title: Quantum-limited metrology and Bose-Einstein condensates
Authors: Sergio Boixo, Animesh Datta, Matthew J. Davis, Anil Shaji, Alexandre
   B. Tacla and Carlton M. Caves
Categories: quant-ph
Comments: 32 pages, 1 figure
\\ ( http://arxiv.org/abs/0906.0962 , 114kb)

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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