# Matt's arXiv selection, Monday 3 July 2006.

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Mon, 3 Jul 2006 10:03:57 +1000 (EST)

The following message was sent to the matts_arxiv list by Matthew Davis <mdavis_at_physics.uq.edu.au>

This week's email is on time and hence a little shorter!

A highlight this week is a review article:

"Ultracold atomic gases in optical lattices: Mimicking condensed matter
physics and beyond"

by Maciej Lewenstein and co-authors.

The abstracts:

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Paper: cond-mat/0606672
Date: Mon, 26 Jun 2006 20:03:43 GMT (14kb)

Title: Shot noise of amplitude of interference between independent atomic
systems
Authors: Anatoli Polkovnikov
Subj-class: Statistical Mechanics; Disordered Systems and Neural Networks
\\
We study shot (counting) noise of the amplitude of interference between
independent atomic systems. We show that for the two interfering systems the
variance of fringe amplitudes decreases as inverse power of the number of
particles per system with the coefficient being a non-universal number. This
number depends on the details of the initial state of each system implying that
the shot noise measurements can be used to distinguish between different
interfering states. We explicitly evaluate this coefficient for the two cases
of interference between bosons in two number states and in two broken symmetry
states with uncorrelated phases. We generalize our analysis to the interference
of multiple independent atomic systems. We show that the variance of the
properly defined interference contrast vanishes inversely proportionally to the
number of systems. This result, implying high signal to noise ratio in the
experiments measuring interference between multiple independent systems, holds
both for bosons and for fermions.
\\ ( http://arXiv.org/abs/cond-mat/0606672 , 14kb)
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Paper: cond-mat/0606677
Date: Tue, 27 Jun 2006 19:12:13 GMT (635kb)

Title: Response of Bose gases in time-dependent optical superlattices
Authors: M. Hild, F. Schmitt, R. Roth
Subj-class: Statistical Mechanics
\\
The dynamic response of ultracold Bose gases in one-dimensional optical
lattices and superlattices is investigated based on an exact numerical time
evolution in the framework of the Bose-Hubbard model. The system is excited by
a temporal amplitude modulation of the lattice potential, as it was already
realized in experiment. For regular lattice potentials, the dynamic signatures
of the superfluid to Mott-insulator transition are studied and the position and
the fine-structure of the resonances is explained by a linear response
analysis. This serves as a preparation for the investigation of dynamical
signatures of quantum phase transitions in two-colour superlattice potentials.
Using direct simulations as well as a perturbative analysis it is shown that
the excitation spectrum changes significantly when going from the homogeneous
Mott-insulator the quasi Bose-glass phase. A characteristic and experimentally
accessible signature for the quasi Bose-glass is the appearance of low-lying
resonances and a suppression of the dominant resonance of the Mott-insulator
phase.
\\ ( http://arXiv.org/abs/cond-mat/0606677 , 635kb)
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Paper: cond-mat/0606684
Date: Tue, 27 Jun 2006 07:44:09 GMT (319kb)

Title: Boojums in Rotating Two-Component Bose-Einstein Condensates
Authors: Hiromitsu Takeuchi and Makoto Tsubota
Subj-class: Other
Journal-ref: J. Phys. Soc. Jpn. 75. 063601 (2006)
\\
A boojum is a topological defect that can form only on the surface of an
ordered medium such as superfluid $^3$He and liquid crystals. We study
theoretically boojums appearing between two phases with different vortex
structures in two-component BECs where the intracomponent interaction is
repulsive in one phase and attractive in the other. The detailed structure of
the boojums is revealed by investigating its density distribution, effective
superflow vorticity and pseudospin texture.
\\ ( http://arXiv.org/abs/cond-mat/0606684 , 319kb)
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Paper: cond-mat/0606697
Date: Tue, 27 Jun 2006 14:59:14 GMT (266kb)

Title: Fermionic atoms trapped in one-dimensional optical superlattice with
harmonic confinement
Authors: Takanori Yamashita, Norio Kawakami, Makoto Yamashita
Subj-class: Statistical Mechanics
\\
We study the ground-state properties of spin-1/2 fermionic atoms confined in
a one-dimensional optical superlattice with harmonic confinement by using the
density matrix renormalization group method. For this purpose, we consider an
ionic Hubbard model that has superlattice potentials with 2-site periodicity.
We find that several different types of insulating regimes coexist even if the
number of atoms at each site is not an integer, but its average within the unit
cell is an integer or half integer. This is contrasted to the coexisting phase
of the metallic and Mott-insulating regimes known for the ordinary Hubbard
model in an optical lattice. The phase characteristics are elucidated by
investigating the profiles of the atom density, the local density/spin
fluctuations, the double occupation probability and the spin correlations in
detail.
\\ ( http://arXiv.org/abs/cond-mat/0606697 , 266kb)
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Paper: cond-mat/0506034
replaced with revised version Tue, 27 Jun 2006 15:19:58 GMT (66kb)

Title: Weakly Interacting, Dilute Bose Gases in 2D
Authors: Anna Posazhennikova
Comments: Survey, 25 pages RMP style, revised version, refs added, some changes
made, accepted for publication in Rev. Mod. Phys
Subj-class: Other; Statistical Mechanics
\\ ( http://arXiv.org/abs/cond-mat/0506034 , 66kb)
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Paper: cond-mat/0511347
replaced with revised version Tue, 27 Jun 2006 13:22:21 GMT (173kb)

Title: Dynamics of the Bose-Einstein condensation: analogy with the collapse
dynamics of a classical self-gravitating Brownian gas
Authors: Julien Sopik, Clement Sire and Pierre-Henri Chavanis
Subj-class: Statistical Mechanics
\\ ( http://arXiv.org/abs/cond-mat/0511347 , 173kb)
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Paper: cond-mat/0606706
Date: Wed, 28 Jun 2006 05:38:23 GMT (92kb)

Title: Superfluidity and non-monogamous pairing at unitarity
Authors: Dean Lee (North Carolina State University)
Subj-class: Statistical Mechanics; Superconductivity
\\
We present lattice results for spin-1/2 fermions at unitarity, where the
effective range of the interaction is zero and the scattering length is
infinite. We measure the spatial coherence of difermion pairs for a system of
6, 10, 14, 18, 22, 26 particles with equal numbers of up and down spins in a
periodic cube. Using Euclidean time projection, we analyze ground state
properties and transient behavior due to low-energy excitations. The results
indicate a low-energy excitation consistent with two quasiparticles moving in
opposite directions at approximately 0.8 times the Fermi momentum. However the
excitation lies well below twice the pairing gap estimated from even-odd ground
state energy staggering and couples strongly to the difermion order parameter.
In order to explain this we develop a theoretical framework for non-monogamous
pairing and an interpretation of the two-quasiparticle excitation as two
countermoving half rotons.
\\ ( http://arXiv.org/abs/cond-mat/0606706 , 92kb)
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Paper: cond-mat/0606709
Date: Wed, 28 Jun 2006 00:03:39 GMT (123kb)

Title: Absence of Fragmentation in Two-Dimensional Bose-Einstein Condensation
Authors: Juan Pablo Fern\'andez and William J. Mullin
Subj-class: Statistical Mechanics
Journal-ref: J. Low Temp. Phys. 138, 687 (2005)
\\
We investigate the possibility that the BEC-like phenomena recently detected
on two-dimensional finite trapped systems consist of fragmented condensates. We
derive and diagonalize the one-body density matrix of a two-dimensional
isotropically trapped Bose gas at finite temperature. For the ideal gas, the
procedure reproduces the exact harmonic-oscillator eigenfunctions and the Bose
distribution. We use a new collocation-minimization method to study the
interacting gas in the Hartree-Fock approximation and obtain a ground-state
wavefunction and condensate fraction consistent with those obtained by other
methods. The populations of the next few eigenstates increase at the expense of
the ground state but continue to be negligible; this supports the conclusion
that two-dimensional BEC is into a single state.
\\ ( http://arXiv.org/abs/cond-mat/0606709 , 123kb)
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Paper: cond-mat/0606710
Date: Wed, 28 Jun 2006 00:15:27 GMT (169kb)

Title: Path-integral Monte Carlo and the squeezed trapped Bose-Einstein gas
Authors: Juan Pablo Fern\'andez and William J. Mullin
Subj-class: Statistical Mechanics
\\
Bose-Einstein condensation has been experimentally found to take place in
finite trapped systems when one of the confining frequencies is increased until
the gas becomes effectively two-dimensional (2D). We confirm the plausibility
of this result by performing path-integral Monte Carlo (PIMC) simulations of
trapped Bose gases of increasing anisotropy and comparing them to the
predictions of finite-temperature many-body theory. PIMC simulations provide an
essentially exact description of these systems; they yield the density profile
directly and provide two different estimates for the condensate fraction. For
the ideal gas, we find that the PIMC column density of the squeezed gas
corresponds quite accurately to that of the exact analytic solution and,
moreover, is well mimicked by the density of a 2D gas at the same temperature;
the two estimates for the condensate fraction bracket the exact result. For the
interacting case, we find 2D Hartree-Fock solutions whose density profiles
coincide quite well with the PIMC column densities and whose predictions for
the condensate fraction are again bracketed by the PIMC estimates.
\\ ( http://arXiv.org/abs/cond-mat/0606710 , 169kb)
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Paper: cond-mat/0605048
replaced with revised version Wed, 28 Jun 2006 06:37:21 GMT (182kb)

Title: Deviation from one-dimensionality in stationary properties and
collisional dynamics of matter-wave solitons
Authors: Lev Khaykovich, Boris A. Malomed
Subj-class: Other
\\ ( http://arXiv.org/abs/cond-mat/0605048 , 182kb)
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Paper: quant-ph/0606233
Date: Wed, 28 Jun 2006 12:21:01 GMT (129kb)

Title: Collective Two-Atom Effects and Trapping States in the Micromaser
Authors: Per K. Rekdal and Bo-Sture K. Skagerstam
\\
We investigate signals of trapping states in the micromaser system in terms
of the average number of cavity photons as well as a suitably defined
correlation length of atoms leaving the cavity. In the description of
collective two-atom effects we allow the mean number of pump atoms inside the
cavity during the characteristic atomic cavity transit time to be as large as
of order one. The master equation we consider, which describes the micromaser
including collective two-atom effects, still exhibits trapping states for even
for a mean number of atoms inside the cavity close to one. We, however, argue
more importantly that the trapping states are more pronounced in terms of the
correlation length as compared to the average number of cavity photons, i.e. we
suggest that trapping states can be more clearly revealed experimentally in
terms of the atom correlation length. For axion detection in the micromaser
this observable may therefore be an essential ingredient.
\\ ( http://arXiv.org/abs/quant-ph/0606233 , 129kb)
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Paper: quant-ph/0606234
Date: Wed, 28 Jun 2006 14:08:56 GMT (291kb)

Title: Experimental Observation of Four-Photon Entangled Dicke State with High
Fidelity
Authors: Nikolai Kiesel, Christian Schmid, Geza Toth, Enrique Solano, and
Harald Weinfurter
Comments: 5 pages, 3 figures, submitted
\\
We present the experimental observation of the symmetric four-photon
entangled Dicke state with two excitations $|D_{4}^{(2)}>$. A simple
experimental set-up allowed quantum state tomography yielding a fidelity as
high as $0.844 \pm 0.008$. We study the entanglement persistency of the state
using novel witness operators and focus on the demonstration of a remarkable
property: depending on the orientation of a measurement on one photon, the
remaining three photons are projected into both inequivalent classes of genuine
tripartite entanglement, the GHZ and W class. Furthermore, we discuss possible
applications of $|D_{4}^{(2)}>$ in quantum communication.
\\ ( http://arXiv.org/abs/quant-ph/0606234 , 291kb)
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Paper (*cross-listing*): quant-ph/0507090
Date: Sat, 9 Jul 2005 04:42:22 GMT (147kb)
Date (revised v2): Mon, 25 Jul 2005 18:41:25 GMT (147kb)

Title: On the unique possibility to increase significantly the contrast of
dark resonances on D1 line of $^{87}$Rb
Authors: A.V. Taichenachev, V.I. Yudin, V.L. Velichansky, and S.A. Zibrov
Categories: quant-ph
Comments: 9 pages, 7 figures. This material has been partially presented on
ICONO-2005, 14 May 2005, St. Petersburg, Russia. v2 references added; text is
changed a bit
Subj-class: Quantum Physics; Atomic Physics
\\
We propose and study, theoretically and experimentally, a new scheme of
excitation of a coherent population trapping resonance for D1 line of alakli
atoms with nuclear spin $I=3/2$ by bichromatic linearly polarized light ({\em
lin}$||${\em lin} field) at the conditions of spectral resolution of the
excited state. The unique properties of this scheme result in a high contrast
of dark resonance for D1 line of $^{87}$Rb.
\\ ( http://arXiv.org/abs/quant-ph/0507090 , 147kb)
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Paper: cond-mat/0606743
Date: Thu, 29 Jun 2006 03:37:03 GMT (19kb)

Title: Predicted quantum stripe ordering in optical lattices
Authors: Congjun Wu, W. Vincent Liu, Joel Moore, and Sankar Das Sarma
Subj-class: Strongly Correlated Electrons; Superconductivity
\\
We predict the robust existence of a novel quantum orbital stripe order in
the $p$-band Bose-Hubbard model of two-dimensional triangular optical lattices
with cold bosonic atoms. An orbital angular momentum moment is formed on each
site exhibiting a stripe order both in the superfluid and Mott-insulating
phases. The stripe order spontaneously breaks time-reversal, lattice
translation and rotation symmetries. In addition, it induces staggered
plaquette bond currents in the superfluid phase. Possible signatures of this
stripe order in the time of flight experiment are discussed.
\\ ( http://arXiv.org/abs/cond-mat/0606743 , 19kb)
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Paper: cond-mat/0606755
Date: Thu, 29 Jun 2006 08:45:49 GMT (96kb)

Title: The Goldstone mode of planar optical parametric oscillators
Authors: Michiel Wouters and Iacopo Carusotto
Subj-class: Other
\\
We propose an experimental setup to probe the low-lying excitation modes of a
parametrically oscillating planar cavity, in particular the soft Goldstone mode
which appears as a consequence of the spontaneously broken U(1) symmetry of
signal/idler phase rotations. Differently from the case of thermodynamical
equilibrium, the Goldstone mode of such a driven-dissipative system is an
overdamped mode, whose linewidth goes to zero in the long-wavelength limit.
When the phase of the signal/idler emission is pinned by an additional laser
beam in the vicinity of the signal emission, the U(1) symmetry is explicitely
broken and a gap opens in the Goldstone mode dispersion. This results in a
dramatic broadening of the response to the probe. Quantitative predictions are
given for the case of semiconductor planar cavities in the strong
exciton-photon coupling regime.
\\ ( http://arXiv.org/abs/cond-mat/0606755 , 96kb)
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Paper: cond-mat/0606757
Date: Thu, 29 Jun 2006 09:16:41 GMT (64kb)

Title: Control of the interaction in a Fermi-Bose mixture
Authors: M. Zaccanti, C. D'Errico, F. Ferlaino, G.Roati, M. Inguscio, G.
Modugno
Subj-class: Other
\\
We control the interspecies interaction in a two-species atomic quantum
mixture by tuning the magnetic field at a Feshbach resonance. The mixture is
composed by fermionic 40K and bosonic 87Rb. We observe effects of the large
attractive and repulsive interaction energy across the resonance, such as
collapse and spatial separation of the mixture, which we use to accurately
locate the resonance position. Understanding and controlling instabilities in
this mixture opens the way to a variety of applications, including formation of
heteronuclear molecular quantum gases.
\\ ( http://arXiv.org/abs/cond-mat/0606757 , 64kb)
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Paper: cond-mat/0606771
Date: Thu, 29 Jun 2006 14:48:20 GMT (2669kb)

Title: Ultracold atomic gases in optical lattices: Mimicking condensed matter
physics and beyond
Authors: Maciej Lewenstein, Anna Sanpera, Veronica Ahufinger, Bogdan Damski,
figures
Report-no: LAUR-06-4002
Subj-class: Other
\\
We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the methods of treatment of such systems, we discuss in detail, which
challenges of condensed matter physics can be addressed with (i) disordered
ultracold lattice gases, (ii) frustrated ultracold gases, (iii) spinor lattice
gases, (iv) lattice gases in "artificial" magnetic fields, and, last but not
least, (v) quantum information processing in lattice gases.
\\ ( http://arXiv.org/abs/cond-mat/0606771 , 2669kb)
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Paper (*cross-listing*): math-ph/0606058
Date: Fri, 23 Jun 2006 10:25:44 GMT (24kb)

Title: Rapidly Rotating Bose-Einstein Condensates in Strongly Anharmonic Traps
Authors: M. Correggi, T. Rindler-Daller, J. Yngvason
Subj-class: Mathematical Physics; Statistical Mechanics
\\
We study a rotating Bose-Einstein Condensate in a strongly anharmonic trap
(flat trap with a finite radius) in the framework of 2D Gross-Pitaevskii
theory. We write the coupling constant for the interactions between the gas
atoms as $1/\epsilon^2$ and we are interested in the limit $\epsilon\to 0$ (TF
limit) with the angular velocity $\Omega$ depending on $\epsilon$. We derive
rigorously the leading asymptotics of the ground state energy and the density
profile when $\Omega$ tends to infinity as a power of $1/\epsilon$. If
$\Omega(\epsilon)=\Omega_0/\epsilon$ a hole'' (i.e., a region where the
density becomes exponentially small as $1/\epsilon\to\infty$) develops for
$\Omega_0$ above a certain critical value. If $\Omega(\epsilon)\gg 1/\epsilon$
the hole essentially exhausts the container and a giant vortex'' develops
with the density concentrated in a thin layer at the boundary.
\\ ( http://arXiv.org/abs/math-ph/0606058 , 24kb)
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Paper: cond-mat/0605143
replaced with revised version Thu, 29 Jun 2006 14:15:25 GMT (68kb)

Title: Classification of zero-energy resonances by dissociation of Feshbach
molecules
Authors: Thomas M. Hanna, Krzysztof Goral, Emilia Witkowska, Thorsten Koehler
Comments: 10 pages, 5 eps figures
Subj-class: Other
\\ ( http://arXiv.org/abs/cond-mat/0605143 , 68kb)
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Paper: physics/0606249
Date: Wed, 28 Jun 2006 21:05:50 GMT (8kb)

Title: Frequency shift of cesium clock transition due to blackbody radiation
Authors: E. J. Angstmann, V. A. Dzuba and V. V. Flambaum
Comments: Accepted for publication in Phys. Rev. Lett
Subj-class: Atomic Physics
\\
We have performed ab initio calculations of the frequency shift induced by a
static electric field on the cesium clock hyperfine transition. The
calculations are used to find the frequency shifts due to blackbody radiation.
Our result ($\delta \nu/E^2=-2.26(2)\times 10^{-10}$Hz/(V/m)$^2$) is in good
agreement with early measurements and ab initio calculations performed in other
groups. We present arguments against recent claims that the actual value of the
effect might be smaller. The difference ($\sim$ 10%) between ab initio and
semiempirical calculations is due to the contribution of the continuum spectrum
to the sum over intermediate states.
\\ ( http://arXiv.org/abs/physics/0606249 , 8kb)
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Paper: physics/0606214
replaced with revised version Thu, 29 Jun 2006 12:53:35 GMT (89kb)

Title: Optical Lattice Polarization Effects on Hyperpolarizability of Atomic
Clock Transitions
Authors: A. V. Taichenachev and V. I. Yudin, V. D. Ovsiannikov, V. G.
Pal'chikov
Comments: 4 pages, RevTeX4, 2 eps figs
Subj-class: Atomic Physics; Optics
\\ ( http://arXiv.org/abs/physics/0606214 , 89kb)
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Till next time,
Matt.

--
=========================================================================
Dr M. J. Davis,               Senior Lecturer in Physics
School of Physical Sciences,  email: mdavis_at_physics.uq.edu.au
University of Queensland,     ph   : +61 7 334 69824
Brisbane, QLD 4072,           fax  : +61 7 336 51242
Australia.                    http://www.physics.uq.edu.au/people/mdavis/
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Received on Mon Jul 03 2006 - 10:03:57 EST

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