Matt's arXiv selection, Monday 24th April 2006.

From: Matthew Davis <>
Date: Mon, 24 Apr 2006 13:21:59 +1000 (EST)

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If you are interested in a 3 year postdoctoral fellow position in sunny Brisbane
you don't have much time left:

On with the abstracts for this week:

Paper: cond-mat/0604416
Date: Tue, 18 Apr 2006 14:32:08 GMT (157kb)

Title: Crossover States of Vortex Matter in Trapped Bose Condensates
Authors: S. Kragset, E. Babaev and A. Sudbo
Comments: 5 pages, 4 figures
Subj-class: Statistical Mechanics
   We perform Monte Carlo studies of vortices in three dimensions in a
cylindrical confinement, with uniform and nonuniform density. The former is
relevant to rotating 4He, the latter is relevant to a rotating trapped Bose
condensate. In the former case we find dominant angular thermal vortex
fluctuations close to the cylinder wall. For the latter case, a novel effect is
that at low temperatures the vortex solid close to the center of the trap
crosses directly over to a tension-less vortex tangle near the edge of the
trap. At higher temperatures an intermediate tension-full vortex liquid located
between the vortex solid and the vortex tangle, may exist.
\\ ( , 157kb)
Paper: cond-mat/0604423
Date: Tue, 18 Apr 2006 19:02:08 GMT (48kb)

Title: Breakdown of the Local Density Approximation in Interacting Systems of
   Cold Fermions in Strongly Anisotropic Traps
Authors: Adilet Imambekov, C. J. Bolech, Mikhail Lukin, and Eugene Demler
Comments: 4+e pages, 3 figures
Subj-class: Strongly Correlated Electrons
   We consider spin polarized mixtures of cold fermionic atoms on the BEC side
of the Feshbach resonance. We demonstrate that a strongly anisotropic confining
potential can give rise to a double peak structure in the axial distribution of
the density difference and a polarization dependent aspect ratio of the
minority species. We point out that both phenomena are not necessarily related
to phase separation and may appear as a result of the breakdown of the local
density approximation. We speculate on the implications of our findings for the
unitary regime.
\\ ( , 48kb)
Paper: cond-mat/0604424
Date: Tue, 18 Apr 2006 19:06:23 GMT (131kb)

Title: Non-BCS superfluidity in trapped ultracold Fermi gases
Authors: L. M. Jensen, J. Kinnunen, and P. Torma
Comments: 4 pages, 4 figures
Subj-class: Strongly Correlated Electrons; Other
   Superconductivity and superfluidity of Fermions require, within the BCS
theory, matching of the Fermi energies of the two interacting Fermion species.
Difference in the number densities of the two species leads either to a normal
state, to phase separation, or - potentially - to exotic forms of superfluidity
such as FFLO-state, Sarma state or breached pair state. Such superfluidity is
of interest e.g. in condensed matter, high-energy and nuclear physics, but firm
experimental evidence is lacking. With the recently realized superfluids of
alkali Fermi gases, the first studies of density-imbalanced gases have shown
that these systems offer unprecedented opportunities for investigating this
question. Here we show that, due to the gases being trapped and isolated from
the environment in terms of particle exchange, exotic forms of superfluidity
appear as a shell around the BCS-superfluid core of the gas and, for large
density imbalance, in the core as well.
\\ ( , 131kb)
Paper: cond-mat/0601681
replaced with revised version Mon, 17 Apr 2006 22:22:49 GMT (226kb)

Title: Exact Study of the 1D Boson Hubbard Model with a Superlattice Potential
Authors: V.G. Rousseau, M. Rigol, F. H\'ebert, D.P. Arovas, G.G. Batrouni, R.T.
Comments: 12 pages, 22 figures
Subj-class: Other; Strongly Correlated Electrons
\\ ( , 226kb)
Paper: quant-ph/0511162
replaced with revised version Tue, 18 Apr 2006 09:38:13 GMT (196kb)

Title: Quantum phase transitions without thermodynamic limits
Authors: Dorje C. Brody, Daniel W. Hook, and Lane P. Hughston
Comments: 4 Pages, further references added
Subj-class: Quantum Physics; Statistical Mechanics
\\ ( , 196kb)
Paper: quant-ph/0604128
Date: Tue, 18 Apr 2006 08:46:55 GMT (46kb)

Title: Generating superposition and entanglement of squeezed vacuum states
Authors: Zhi-Ming Zhang
Comments: 5 pages, 3 figures
   We propose a scheme for generating the superposition and the entanglement of
squeezed vacuum states of electromagnetical fields. The scheme involves
single-photon source, single photon detector, and cross Kerr nonlinearity. The
Kerr nonlinearity required for generating the superposition of squeezed vacuum
states is 1/2 of that required for generating the superposition of coherent
states. The proposal can also be extended to generate the entanglement states
between two coherent states and that between one coherent state and one
squeezed vacuum state.
\\ ( , 46kb)
Paper: quant-ph/0604134
Date: Tue, 18 Apr 2006 19:55:21 GMT (395kb)

Title: Experimental continuous-variable entanglement of phase-locked bright
   optical beams
Authors: Jietai Jing, Sheng Feng, Russell Bloomer, Olivier Pfister
Comments: 4 pages, 5 figures, submitted for publication
   We observed continuous-variable entanglement between two bright beams emitted
above threshold by a phase-difference-locked ultrastable optical parametric
oscillator. The amplitude-difference squeezing is -3 dB and the phase-sum one
is -1.35 dB. The beams are classically phase-locked at a frequency difference
of 161.8273240(5) MHz, continuously tunable by the OPO crystal temperature.
Such unprecedented frequency-difference stability paves the way for
implementing quantum frequency multiplexing and CV quantum information in the
frequency domain.
\\ ( , 385kb)
Paper: physics/0604139
Date: Tue, 18 Apr 2006 14:55:36 GMT (116kb)

Title: Efficient formation of strongly bound ultracold cesium molecules by
   photoassociation with tunneling
Authors: Mihaela Vatasescu, Claude M. Dion, and Olivier Dulieu
Comments: 15 pages with 7 figures. Submitted to J. Phys. B
Subj-class: Atomic Physics; Chemical Physics
   We calculate the rates of formation and detection of ultracold Cs_2 molecules
obtained from the photoassociation of ultracold atoms through the double-well
0g- (6S1/2 + 6P3/2) state. We concentrate on two features previously observed
experimentally and attributed to tunneling between the two wells [Vatasescu et
al 2000 Phys. Rev. A 61 044701]. We show that the molecules obtained are in
strongly bound levels (v''=5,6) of the metastable a 3Sigma_u+ (6S1/2 + 6S1/2)
ground electronic state.
\\ ( , 116kb)
Paper: physics/0604140
Date: Tue, 18 Apr 2006 15:55:37 GMT (288kb)

Title: Theoretical model for ultracold molecule formation via adaptive feedback
Authors: Ulrich Poschinger, Wenzel Salzmann, Roland Wester, Matthias
   Weidemueller, Christiane P. Koch, Ronnie Kosloff
Subj-class: Atomic Physics
   We investigate pump-dump photoassociation of ultracold molecules with
amplitude- and phase-modulated femtosecond laser pulses. For this purpose a
perturbative model for the light-matter interaction is developed and combined
with a genetic algorithm for adaptive feedback control of the laser pulse
shapes. The model is applied to the formation of 85Rb2 molecules in a
magneto-optical trap. We find for optimized pulse shapes an improvement for the
formation of ground state molecules by more than a factor of 10 compared to
unshaped pulses at the same pump-dump delay time, and by 40% compared to
unshaped pulses at the respective optimal pump-dump delay time. Since our model
yields directly the spectral amplitudes and phases of the optimized pulses, the
results are directly applicable in pulse shaping experiments.
\\ ( , 288kb)
Paper: physics/0604130
Date: Tue, 18 Apr 2006 00:33:14 GMT (28kb)

Title: Finding Scientific Gems with Google
Authors: P. Chen, H. Xie, S. Maslov, and S. Redner
Comments: 6 pages, 4 figures, 2 tables, 2-column revtex4 format
Subj-class: Data Analysis, Statistics and Probability; Physics and Society
   We apply the Google PageRank algorithm to assess the relative importance of
all publications in the Physical Review family of journals from 1893--2003.
While the Google number and the number of citations for each publication are
positively correlated, outliers from this linear relation identify some
exceptional papers or "gems" that are universally familiar to physicists.
\\ ( , 28kb)
Paper: cond-mat/0604432
Date: Wed, 19 Apr 2006 03:26:11 GMT (35kb)

Title: Dipolar Bose gases: Many-body versus mean-field description
Authors: D.C.E. Bortolotti, S. Ronen, J.L. Bohn, D. Blume
Subj-class: Statistical Mechanics
   We characterize zero-temperature dipolar Bose gases under external spherical
confinement as a function of the dipole strength using the essentially exact
many-body diffusion Monte Carlo (DMC) technique. We show that the DMC energies
are reproduced accurately within a mean-field framework if the variation of the
s-wave scattering length with the dipole strength is accounted for properly.
Our calculations suggest stability diagrams and collapse mechanisms of dipolar
Bose gases that differ significantly from those previously proposed in the
\\ ( , 35kb)
Paper: cond-mat/0604455
Date: Wed, 19 Apr 2006 17:52:07 GMT (216kb)

Title: The dynamics of condensate shells: collective modes and expansion
Authors: C. Lannert, T.-C. Wei, and S. Vishveshwara
Subj-class: Other
   We explore the physics of three-dimensional shell-shaped condensates,
relevant to cold atoms in "bubble traps" and to Mott insulator-superfluid
systems in optical lattices. We study the ground state of the condensate
wavefunction, spherically-symmetric collective modes, and expansion properties
of such a shell using a combination of analytical and numerical techniques. We
find two breathing-type modes with frequencies that are distinct from that of
the filled spherical condensate. Upon trap release and subsequent expansion, we
find that the system displays self-interference fringes. We estimate
characteristic time scales, degree of mass accumulation, three-body loss, and
kinetic energy release during expansion for a typical system of Rb87.
\\ ( , 216kb)
Paper: cond-mat/0604458
Date: Wed, 19 Apr 2006 19:30:35 GMT (386kb)

Title: Equations of motion approach to decoherence and current noise in
   ballistic interferometers coupled to a quantum bath
Authors: Florian Marquardt
Comments: 10 pages, 7 figures
Subj-class: Mesoscopic Systems and Quantum Hall Effect
   We present a technique for treating many particles moving inside a ballistic
interferometer, under the influence of a quantum-mechanical environment
(phonons, photons, Nyquist noise etc.). Our approach is based on solving the
coupled Heisenberg equations of motion of the many-particle system and the bath
and is inspired by the quantum Langevin method known for the Caldeira Leggett
model. It allows to study decoherence and the influence of the bath on other
properties of the interferometer. As a first application, we treat a fermionic
Mach-Zehnder interferometer. In particular, we discuss the dephasing rate and
present full analytical expressions for the leading corrections to the current
noise, brought about by the coupling to the quantum bath.
\\ ( , 386kb)
Paper: cond-mat/0504503
replaced with revised version Wed, 19 Apr 2006 08:46:47 GMT (236kb)

Title: Slave particle approach to the finite temperature properties of
   ultracold Bose gases in optical lattices
Authors: Xiancong Lu, Jinbin Li and Yue Yu
Comments: 27 pages, 8 figures, final version for publication
Subj-class: Statistical Mechanics
Journal-ref: Phys. Rev. A 73, 043607 (2006)
\\ ( , 236kb)
Paper: cond-mat/0602201
replaced with revised version Wed, 19 Apr 2006 01:09:45 GMT (29kb)

Title: Strong coupling theory for the superfluidity of Bose-Fermi mixtures
Authors: Daw-Wei Wang
Comments: 4 pages and 3 figures
Subj-class: Other; Superconductivity
Journal-ref: Phys. Rev. Lett. 96, 140404 (2006)
DOI: 10.1103/PhysRevLett.96.140404
\\ ( , 29kb)
Paper: cond-mat/0604063
replaced with revised version Wed, 19 Apr 2006 06:41:16 GMT (12kb)

Title: Disorder-Induced Order: From Classical Spin Systems to Ultracold Atomic
Authors: Jan Wehr (University Of Arizona), Armand Niederberger (ICFO), Laurent
   Sanchez-Palencia (LCFIO), Maciej Lewenstein (ICFO)
Comments: minor changes; references added
Proxy: ccsd ccsd-00022177
Subj-class: Other
\\ ( , 12kb)
Paper: quant-ph/0604144
Date: Wed, 19 Apr 2006 15:48:31 GMT (132kb)

Title: Electronic properties of Francium diatomic compounds and prospects for
   cold molecule formation
Authors: Mireille Aymar (LAC), Olivier Dulieu (LAC), Fernand Spiegelman (LPQ)
Proxy: ccsd ccsd-00023052
   In this work we investigate the possibility to create cold Fr$\_2$, RbFr, and
CsFr molecules through photoassociation of cold atoms. Potential curves,
permanent and transition dipole moments for the Francium dimer and for the RbFr
and RbCs molecules are determined for the first time. The Francium atom is
modelled as a one valence electron moving in the field of the Fr$^+$ core,
which is described by a new pseudopotential with averaged relativistic effects,
and including effective core polarization potential. The molecular calculations
are performed for both the ionic species Fr$\_2^+$, RbFr$^+$, CsFr$^+$ and the
corresponding neutral, through the CIPSI quantum chemistry package where we
used new extended gaussian basis sets for Rb, Cs, and Fr atoms. As no
experimental data is available, we discuss our results by comparison with the
Rb$\_2$, Cs$\_2$, and RbCs systems. The dipole moment of CsFr reveals an
electron transfer yielding a Cs$^+$Fr$^-$ arrangement, while in all other mixed
alkali pairs the electron is transferred towards the lighter species. Finally
the perturbative treatment of the spin-orbit coupling at large distances
predicts that in contrast with Rb$\_2$ and Cs$\_2$, no double-well excited
potential should be present in Fr$\_2$, probably preventing an efficient
formation of cold dimers via photoassociation of cold Francium atoms.
\\ ( , 132kb)
Paper: cond-mat/0604464
Date: Wed, 19 Apr 2006 23:23:40 GMT (117kb)

Title: Quantum theory of an atom laser originating from a Bose-Einstein
   condensate or a Fermi gas in the presence of gravity
Authors: Tobias Kramer and Mirta Rodriguez
Comments: 12 pages, 8 figures
Subj-class: Other
   We present a 3D quantum mechanical theory of radio-frequency outcoupled atom
lasers from trapped atomic gases in the presence of the gravitational force.
Predictions for the total outcoupling rate as a function of the radio-frequency
and for the beam wave function are given. We establish a sum rule for the
energy integrated outcoupling, which leads to a separate determination of the
coupling strength between the atoms and the radiation field.
   For a non-interacting Bose-Einstein condensate analytic solutions are derived
which are subsequently extended to include the effects of atomic interactions.
The interactions enhance interference effects in the beam profile and modify
the outcoupling rate of the atom laser. We provide a complete quantum
mechanical solution which is in line with experimental findings and allows to
determine the validity of commonly used approximative methods.
   We also extend the formalism to a fermionic atom laser and analyze the effect
of superfluidity on the outcoupling of atoms.
\\ ( , 117kb)
Paper: cond-mat/0604469
Date: Thu, 20 Apr 2006 07:19:00 GMT (109kb)

Title: Finite Temperature Momentum Distribution of a Trapped Fermi Gas
Authors: Qijin Chen, C. A. Regal, D. S. Jin, and K. Levin
Comments: 5 pages, 3 figures
Subj-class: Strongly Correlated Electrons; Superconductivity
   We present measurements of the temperature-dependent momentum distribution of
a trapped Fermi gas consisting of $^{40}$K in the BCS-BEC crossover regime.
Accompanying theoretical results based upon a simple mean-field ground state
are compared to the experimental data. Non-monotonic effects associated with
temperature, $T$, arise from the competition between thermal broadening and a
narrowing of the distribution induced by the decrease in the excitation gap
$\Delta(T)$ with increasing $T$.
\\ ( , 109kb)
Paper: cond-mat/0604476
Date: Thu, 20 Apr 2006 10:08:52 GMT (155kb)

Title: Relaxation in a completely integrable many-body quantum system: an {\it
   ab initio} study of the dynamics of the highly excited states of lattice
   hard-core bosons
Authors: Marcos Rigol (1), Vanja Dunjko (2), Vladimir Yurovsky (3), Maxim
   Olshanii (2) ((1) UC Davis, (2) USC, (3) U Tel Aviv)
Comments: 4 pages, 2 figures
Subj-class: Other
   In this article we pose the question of whether a many-body quantum system
with a full set of conserved quantities can undergo an irreversible relaxation
to an equilibrium state, and, if it can, what this state is. We confirm the
relaxation hypothesis through a thorough ab initio numerical investigation of
the dynamics of hard-core bosons on a one-dimensional lattice. Further, a
natural extension of the Gibbs ensemble to integrable systems results in a
theory that is able to predict the equilibrium state after relaxation. The
theoretical and numerical results are in excellent agreement. Finally, we show
that our generalized equilibrium carries more memory of the initial conditions
than the usual thermodynamic one. This effect may have many experimental
consequences, some of which having already been observed in the recent
experiment on the non-equilibrium dynamics of one-dimensional hard-core bosons
in a harmonic potential [T. Kinoshita, T. Wenger, D.S. Weiss, Nature (London)
440, 900 (2006)].
\\ ( , 155kb)
Paper: cond-mat/0603643
replaced with revised version Thu, 20 Apr 2006 13:10:01 GMT (61kb)

Title: The 1D interacting anyon gas: low-energy properties and Haldane
   exclusion statistics
Authors: M.T. Batchelor, X.-W. Guan and N. Oelkers
Comments: 4 pages, 2 figures, improved text, references added
Subj-class: Statistical Mechanics
\\ ( , 61kb)

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
Received on Mon Apr 24 2006 - 13:21:59 EST

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