# [Matts-arxiv] Matt's arXiv selection: week ending 14 August 2009

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Sun, 20 Sep 2009 10:14:22 +1000

Dear subscribers,

This instalment is coming to you from Singapore airport. Geoff Lee compiled
this week's abstracts, of which 14 are new and 14 are replacements:

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arXiv:0908.1002
Date: Fri, 7 Aug 2009 08:33:28 GMT (16kb)

Title: Temperature dependence of critical velocities and long time decay of
supercurrents
Authors: Yongle Yu
Categories: cond-mat.supr-con
\\
We show that a microscopic theory of superfluidity, based on the properties
of the many-body spectrum of a superfluid, can explain naturally the
temperature dependence of critical velocities and the long time decay of
supercurrents.
\\ ( http://arxiv.org/abs/0908.1002 , 16kb)
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arXiv:0908.1009
Date: Fri, 7 Aug 2009 12:05:16 GMT (1337kb)

Title: Phonon instability and self-organized structures in multi-layer stacks
of confined dipolar Bose-Einstein condensates in optical lattices
Authors: Patrick K\"oberle, G\"unter Wunner
Categories: cond-mat.quant-gas cond-mat.other
\\
In calculations to date [1,2] of multi-layer stacks of dipolar condensates,
created in one-dimensional optical lattices, the condensates have been assumed
to be two-dimensional. In a real experiment, however, the condensates do not
extend to infinity in the oblate direction, but have to be confined by a trap
potential, too. By three-dimensional numerical simulations of this realistic
experimental situation we find a crucial dependence of the phonon instability
boundary on the number of layers. Moreover, near the boundary of the phonon
instability, a variety of structured ground-state wave functions emerges, which
may indicate the onset of a roton instability [3,4].
\\ ( http://arxiv.org/abs/0908.1009 , 1337kb)
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arXiv:0908.1073
Date: Fri, 7 Aug 2009 15:29:05 GMT (42kb)

Title: Universal scaling in a trapped Fermi super-fluid in the BCS-unitarity
crossover
Categories: cond-mat.quant-gas
\\
Using numerical simulation based on a density-functional equation for a
trapped Fermi super-fluid valid along the BCS-unitarity crossover, we establish
robust scaling over many orders of magnitude in the observables of the system
as a function of fermion number. This scaling allows to predict the static
properties of the system, such as energy, chemical potential, etc., for a large
number of fermions, over the crossover, from the knowledge of those for a small
number ($\sim 4-10$) of fermions.
\\ ( http://arxiv.org/abs/0908.1073 , 42kb)
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arXiv:0908.1101
Date: Fri, 7 Aug 2009 19:07:45 GMT (422kb)

Title: Collisional Stability of 40K Immersed in a Strongly Interacting Fermi
Gas of 6Li
Authors: F. M. Spiegelhalder, A. Trenkwalder, D. Naik, G. Hendl, F. Schreck, R.
Grimm
Categories: cond-mat.quant-gas
\\
We investigate the collisional stability of a sample of 40K atoms immersed in
a tunable spin mixture of 6Li atoms. For large negative scattering lengths
between the two 6Li spin states, we measure very low loss rates and demonstrate
the all-optical preparation of a double-degenerate Fermi-Fermi mixture. For a
strongly interacting 6Li Fermi gas with resonant interactions, we find
sufficient collisional stability for interspecies thermalization.
\\ ( http://arxiv.org/abs/0908.1101 , 422kb)
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arXiv:0908.1151
Date: Sat, 8 Aug 2009 06:28:57 GMT (1146kb,D)

Title: Stability and collapse of localized solutions of the controlled
three-dimensional Gross-Pitaevskii equation
Authors: Renato Fedele, Dusan Jovanovic, Bengt Eliasson, Sergio De Nicola,
Categories: cond-mat.quant-gas
\\
On the basis of recent investigations, a newly developed analytical procedure
is used for constructing a wide class of localized solutions of the controlled
three-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the
dynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is
decomposed into a two-dimensional (2D) linear Schr\"{o}dinger equation and a
one-dimensional (1D) nonlinear Schr\"{o}dinger equation, constrained by a
variational condition for the controlling potential. Then, the above class of
localized solutions are constructed as the product of the solutions of the
transverse and longitudinal equations. On the basis of these exact 3D
analytical solutions, a stability analysis is carried out, focusing our
attention on the physical conditions for having collapsing or non-collapsing
solutions.
\\ ( http://arxiv.org/abs/0908.1151 , 1146kb)
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arXiv:0908.1182
Date: Sat, 8 Aug 2009 18:57:16 GMT (2859kb)

Title: Disordered insulator in an optical lattice
Authors: M. Pasienski, D. McKay, M. White, and B. DeMarco
Categories: cond-mat.quant-gas cond-mat.dis-nn
\\
Disorder can profoundly affect the transport properties of a wide range of
quantum materials. For example, the superfluid transition temperature for
helium is strongly modified when it is adsorbed in porous media, and
understanding how disorder affects the emergence of high-temperature
superconductivity is a problem with critical implications for both practical
applications and fundamental condensed matter physics. Presently, there is
significant disagreement regarding the effect of disorder on transport in the
disordered Bose-Hubbard (DBH) model--the paradigm used to theoretically study
disorder in strongly correlated bosonic systems. We experimentally realize the
DBH model by using optical speckle to introduce precisely known, controllable,
and fine-grained disorder to an optical lattice. Here, we show that disorder
can induce a SF-to-insulator (IN) transition in this system, but we find no
evidence for a disorder-generated IN-to-SF transition, in conflict with certain
theoretical predictions. We find that the transition to an IN is marked by
changes in both the quasimomentum distribution and the dissipation strength for
transport. We probe the quasimomentum distribution using time-of-flight (TOF)
imaging, and the transport properties by measuring the motion of the
centre-of-mass (COM) of the atom gas immediately after an applied impulse. By
correlating these measurements, we determine that the transition from a SF to
an IN is associated with the complete destruction of the condensate by disorder
and the emergence of a localized state. We find that increasing disorder
strength generically leads to greater dissipation in the regime of mixed SF and
Mott-insulator (MI) phases, ruling out theories that predict a disorder-induced
MI-to-SF transition for this system.
\\ ( http://arxiv.org/abs/0908.1182 , 2859kb)
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arXiv:0908.1343
Date: Mon, 10 Aug 2009 15:56:24 GMT (30kb)

Title: Polaron to molecule transition in a strongly imbalanced Fermi gas
Authors: M. Punk, P.T. Dumitrescu, W. Zwerger
Categories: cond-mat.quant-gas
Comments: 10 pages, 4 figures, RevTex4
\\
A single down spin Fermion with an attractive, zero range interaction with a
Fermi sea of up-spin Fermions forms a polaronic quasiparticle. The associated
quasiparticle weight vanishes beyond a critical strength of the attractive
interaction, where a many-body bound state is formed. From a variational
wavefunction in the molecular limit, we determine the critical value for the
polaron to molecule transition. The value agrees well with the diagrammatic
Monte Carlo results of Prokof'ev and Svistunov and is consistent with recent
rf-spectroscopy measurements of the quasiparticle weight by Schirotzek et. al.
In addition, we calculate the contact coefficient of the strongly imbalanced
gas, using the adiabatic theorem of Tan and discuss the implications of the
polaron to molecule transition for the phase diagram of the attractive Fermi
gas at finite imbalance.
\\ ( http://arxiv.org/abs/0908.1343 , 30kb)
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arXiv:0908.0950 (*cross-listing*)
Date: Thu, 6 Aug 2009 20:20:30 GMT (107kb)

Title: Spin response of a normal Fermi liquid with noncentral interactions
Authors: C.J. Pethick, A. Schwenk
Categories: nucl-th astro-ph.HE cond-mat.other
Comments: 9 pages, 2 figures; NORDITA-2009-36
\\
We consider the spin response of a normal Fermi liquid with noncentral
interactions under conditions intermediate between the collisionless and
hydrodynamic regimes. This problem is of importance for calculations of
neutrino properties in dense matter. By expressing the deviation of the
quasiparticle distribution function from equilibrium in terms of eigenfunctions
of the transport equation under the combined influence of collisions and an
external field, we derive a closed expression for the
spin-density--spin-density response function and compare its predictions with
that of a relaxation time approximation. Our results indicate that the
relaxation time approximation is reliable for neutrino properties under
astrophysically relevant conditions.
\\ ( http://arxiv.org/abs/0908.0950 , 107kb)
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arXiv:0908.1483
Date: Tue, 11 Aug 2009 09:09:05 GMT (562kb)

Title: Atom cooling by non-adiabatic expansion
Authors: Xi Chen, J. G. Muga, A. del Campo, A. Ruschhaupt
Categories: quant-ph
\\
Motivated by the recent discovery that a reflecting wall moving with a
square-root in time trajectory behaves as a universal stopper of classical
particles regardless of their initial velocities, we compare linear in time and
square-root in time expansions of a box to achieve efficient atom cooling. For
the quantum single-atom wavefunctions studied the square-root in time expansion
whereas any linear in time (constant box-wall velocity) expansion leaves a
non-zero residual energy, except in the limit of an infinitely slow expansion.
For finite final times and box lengths we set a number of bounds and cooling
principles which again confirm the superior performance of the square-root in
time expansion, even more clearly for increasing excitation of the initial
state. Breakdown of adiabaticity is generally fatal for cooling with the linear
expansion but not so with the square-root expansion.
\\ ( http://arxiv.org/abs/0908.1483 , 562kb)
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arXiv:0908.1569
Date: Tue, 11 Aug 2009 20:00:41 GMT (71kb,D)

Title: Probing phase-separation in Bose-Fermi mixtures by the critical
superfluid velocity
Authors: Jacob Linder and Asle Sudb{\o}
Categories: cond-mat.quant-gas
\\
We investigate the effect exerted by spin-polarized fermions on the
interaction between superfluid bosons for a Bose-Fermi mixture residing on an
optical lattice, with particular emphasis on the possibility of an induced
phase-separation. Using a set of microscopic parameters relevant to a
$^{40}$K-$^{87}$Rb mixture, we show how the phase-separation criterion may be
directly probed by means of the critical superfluid velocity of the bosonic
condensate. We report quantitative results for the magnitude of the superfluid
velocity and its dependence on the trap depth, the boson-fermion interaction,
and the fermionic filling fraction. All of these parameters can be controlled
experimentally in a well-defined manner. We propose an experimental setup for
probing the critical superfluid velocity.
\\ ( http://arxiv.org/abs/0908.1569 , 71kb)
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arXiv:0908.1593
Date: Tue, 11 Aug 2009 22:26:13 GMT (1415kb,D)

Title: Spontaneous Vortex Lattices in Quasi 2D Dipolar Spinor Condensates
Authors: Jian Zhang and Tin-Lun HO
Categories: cond-mat.quant-gas
\\
Motivated by recent experiments\cite{BA}\cite{BB}, we study quasi 2D
ferromagnetic condensates with various aspect ratios. We find that in zero
magnetic field, dipolar energy generates a local energy minimum with all the
spins lie in the 2D plane forming a row of {\em circular} spin textures with
{\em alternating} orientation, corresponding to a packing of vortices of {\em
identical} vorticity in different spin components. In a large magnetic field,
the system can fall into a long lived dynamical state consisting of an array of
elliptic and hyperbolic Mermin-Ho spin textures, while the true equilibrium is
an uniaxial spin density wave with a single wave-vector along the magnetic
field, and a wavelength similar to the characteristic length of the long lived
vortex array state.
\\ ( http://arxiv.org/abs/0908.1593 , 1415kb)
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arXiv:0908.1634
Date: Wed, 12 Aug 2009 08:34:38 GMT (1783kb,D)

Title: Optimal control of number squeezing in trapped Bose-Einstein condensates
Authors: Julian Grond, Gregory von Winckel, Joerg Schmiedmayer, Ulrich
Hohenester
Categories: cond-mat.other
\\
We theoretically analyze atom interferometry based on trapped ultracold
atoms, and employ optimal control theory in order to optimize number squeezing
and condensate trapping. In our simulations, we consider a setup where the
confinement potential is transformed from a single to a double well, which
allows to split the condensate. To avoid in the ensuing phase-accumulation
stage of the interferometer dephasing due to the nonlinear atom-atom
interactions, the atom number fluctuations between the two wells should be
sufficiently low. We show that low number fluctuations (high number squeezing)
can be obtained by optimized splitting protocols. Two types of solutions are
found: in the Josephson regime we find an oscillatory tunnel control and a
parametric amplification of number squeezing, while in the Fock regime
squeezing is obtained solely due to the nonlinear coupling, which is
transformed to number squeezing by peaked tunnel pulses. We study splitting and
squeezing within the frameworks of a generic two-mode model, which allows us to
study the basic physical mechanisms, and the multi-configurational time
dependent Hartree for bosons method, which allows for a microscopic modeling of
the splitting dynamics in realistic experiments. Both models give similar
results, thus highlighting the general nature of these two solution schemes. We
finally analyze our results in the context of atom interferometry.
\\ ( http://arxiv.org/abs/0908.1634 , 1783kb)
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arXiv:0908.1794
Date: Wed, 12 Aug 2009 20:17:54 GMT (108kb)

Title: Improving the efficiency of ultracold dipolar molecule formation by
Authors: J. K. Freericks, M. M. Maska, Anzi Hu, Thomas M. Hanna, C. J.
Williams, P. S. Julienne, and R. Lemanski
Categories: cond-mat.quant-gas
Comments: (5 pages, 3 pages, submitted to Phys. Rev. Lett.)
\\
Ultracold ground state dipolar 40K-87Rb molecules have recently been produced
in a loose harmonic trap by employing a magnetic field sweep across a Feshbach
resonance followed by stimulated Raman adiabatic passage [K.-K. Ni et al.,
Science 322, 231 (2008)]. The overall experimental efficiency for molecule
formation was around 20%. We show that the efficiency can be increased to
nearly 100% if one first loads the atomic gases into an optical lattice of the
appropriate depth and tunes the interspecies attraction to have exactly one
atom of each species at an occupied lattice site. Our proposed scheme provides
a large enhancement to the dipolar molecule density even at relatively high
temperatures, and avoids three-body recombination loss by preventing lattice
sites from being triply occupied.
\\ ( http://arxiv.org/abs/0908.1794 , 108kb)
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arXiv:0908.1947
Date: Thu, 13 Aug 2009 18:15:20 GMT (214kb)

Title: Speed of sound in disordered Bose-Einstein condensates
Authors: Christopher Gaul, Nina Renner, Cord Axel Mueller
Categories: cond-mat.quant-gas
\\
Disorder modifies the sound-wave excitation spectrum of Bose-Einstein
condensates (BEC). We consider the classical hydrodynamic limit, where the
disorder correlation length is much longer than the condensate healing length.
By perturbation theory, we compute the phonon lifetime and correction to the
speed of sound. This correction is found to be negative in all dimensions, with
universal asymptotics for smooth correlations. Considering in detail optical
speckle potentials, we find a quite rich intermediate structure. This has
consequences for the average density of states, particularly in one dimension,
where we find a boson dip'' next to a sharp boson peak'' as function of
frequency. In one dimension, our prediction is verified in detail by a
numerical integration of the Gross-Pitaevskii equation.
\\ ( http://arxiv.org/abs/0908.1947 , 214kb)
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The replacements:

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arXiv:0902.2979
replaced with revised version Fri, 7 Aug 2009 16:49:35 GMT (38kb)

Title: Caustic formation in expanding condensates of cold atoms
Authors: J. T. Chalker, B. Shapiro
Categories: cond-mat.dis-nn cond-mat.other quant-ph
Comments: 10 pages, 5 figures. Published version
Journal-ref: Phys. Rev. A 80, 013603 (2009)
DOI: 10.1103/PhysRevA.80.013603
\\ ( http://arxiv.org/abs/0902.2979 , 38kb)
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arXiv:0904.2062
replaced with revised version Fri, 7 Aug 2009 07:07:51 GMT (2597kb)

Title: Spatially inhomogeneous phase evolution of a two-component Bose-Einstein
condensate
Authors: R. P. Anderson, C. Ticknor, A. I. Sidorov, B. V. Hall
Categories: cond-mat.quant-gas cond-mat.other
Journal-ref: Phys. Rev. A 80, 023603 (2009)
DOI: 10.1103/PhysRevA.80.023603
\\ ( http://arxiv.org/abs/0904.2062 , 2597kb)
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arXiv:0907.1866
replaced with revised version Fri, 7 Aug 2009 19:30:41 GMT (284kb,D)

Title: Density profiles and spin oscillations of an interacting three-component
normal Fermi gas
Authors: Theja N. De Silva
Categories: cond-mat.quant-gas
\\ ( http://arxiv.org/abs/0907.1866 , 284kb)
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arXiv:0908.0590
replaced with revised version Fri, 7 Aug 2009 05:10:04 GMT (394kb)

Title: Detecting Bose-Einstein condensation of exciton-polaritons via electron
transport
Authors: Yueh-Nan Chen, Neill Lambert, Franco Nori
Categories: cond-mat.mes-hall cond-mat.quant-gas
\\ ( http://arxiv.org/abs/0908.0590 , 394kb)
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arXiv:0906.1031
replaced with revised version Fri, 7 Aug 2009 05:01:46 GMT (161kb,D)

Title: Continuous measurement feedback control of a Bose-Einstein condensate
using phase contrast imaging
Authors: S. S. Szigeti, M. R. Hush, A. R. R. Carvalho and J. J. Hope
Categories: quant-ph
Journal-ref: S. S. Szigeti, M. R. Hush, A. R. R. Carvalho and J. J. Hope, Phys.
Rev. A 80, 013614 (2009)
DOI: 10.1103/PhysRevA.80.013614
\\ ( http://arxiv.org/abs/0906.1031 , 161kb)
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arXiv:0807.3893
replaced with revised version Sun, 9 Aug 2009 18:42:39 GMT (672kb)

Title: Decay of soliton-like perturbations into vortex - anti vortex pairs
Categories: cond-mat.other
Comments: 14 pages, 16 figures. Accepted by the Romanian Journal of Physics
\\ ( http://arxiv.org/abs/0807.3893 , 672kb)
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arXiv:0906.2116
replaced with revised version Mon, 10 Aug 2009 16:13:40 GMT (2289kb)

Title: Multi-band spectroscopy of inhomogeneous Mott-insulator states of
ultracold bosons
Authors: D. Clement, N. Fabbri, L. Fallani, C. Fort and M. Inguscio
Categories: cond-mat.quant-gas cond-mat.other
\\ ( http://arxiv.org/abs/0906.2116 , 2289kb)
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arXiv:0907.3659
replaced with revised version Fri, 7 Aug 2009 20:32:30 GMT (26kb)

Title: High-momentum tail in the Tonks-Girardeau gas under general confining
potentials
Authors: Gustavo A. Moreno
Categories: cond-mat.quant-gas
\\ ( http://arxiv.org/abs/0907.3659 , 26kb)
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arXiv:0908.1073
replaced with revised version Mon, 10 Aug 2009 12:50:12 GMT (42kb)

Title: Universal scaling in a trapped Fermi super-fluid in the BCS-unitarity
crossover
Categories: cond-mat.quant-gas
Comments: 4 pages, 4 figures, Contribution to the 18th International Laser
Physics Workshop, Barcelona, Spain, July 13 - 17, 2009
\\ ( http://arxiv.org/abs/0908.1073 , 42kb)
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arXiv:0908.0263
replaced with revised version Sun, 9 Aug 2009 03:55:17 GMT (763kb)

Title: Imaging-based Parametric Resonance in an Optical Dipole Atom Trap
Authors: S. Balik, A.L. Win and M.D. Havey
Categories: quant-ph
Journal-ref: PHYSICAL REVIEW A 80, 023404 (2009)
\\ ( http://arxiv.org/abs/0908.0263 , 763kb)
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arXiv:0905.0257
replaced with revised version Tue, 11 Aug 2009 14:02:01 GMT (672kb)

Title: First and second sound in a strongly interacting Fermi gas
Authors: E. Taylor, H. Hu, X.-J. Liu, L. P. Pitaevskii, A. Griffin, S.
Stringari
Categories: cond-mat.quant-gas
Comments: Updated version. 7 pages, 4 figures
\\ ( http://arxiv.org/abs/0905.0257 , 672kb)
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arXiv:0907.0720
replaced with revised version Tue, 11 Aug 2009 19:33:00 GMT (38kb)

Title: Semiclassical dynamics of atomic Bose-Einstein condensates
Authors: S. Choi and B. Sundaram
Categories: cond-mat.quant-gas quant-ph
Comments: 4 figures. Submitted for publication. v2: includes a couple of new
\\ ( http://arxiv.org/abs/0907.0720 , 38kb)
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arXiv:0901.3148
replaced with revised version Wed, 12 Aug 2009 20:41:28 GMT (112kb)

Title: Heavy-Light Fermion Mixtures at Unitarity
Authors: Alexandros Gezerlis, S. Gandolfi, K. E. Schmidt, J. Carlson
Categories: cond-mat.other cond-mat.quant-gas nucl-th
Comments: 4+ pages, 4 figures; 2 references added; v2 corresponds to the
published version
Report-no: LA-UR 09-00434
Journal-ref: Phys. Rev. Lett. 103, 060403 (2009)
DOI: 10.1103/PhysRevLett.103.060403
\\ ( http://arxiv.org/abs/0901.3148 , 112kb)
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arXiv:0902.0107
replaced with revised version Thu, 13 Aug 2009 16:53:55 GMT (394kb)

Title: One-dimensional Anderson localization in certain correlated random
potentials
Authors: Pierre Lugan (LCFIO), Alain Aspect (LCFIO), Laurent Sanchez-Palencia
(LCFIO), Dominique Delande (LKB - Jussieu), Beno\^it Gr\'emaud (LKB -
Jussieu, IPAL, CNRS), Cord A. M\"uller (LKB - Jussieu), Christian Miniatura
(IPAL, CNRS, INLN)
Categories: cond-mat.other
Journal-ref: Physical Review A: Atomic, Molecular and Optical Physics 80 (2009)
023605
DOI: 10.1103/PhysRevA.80.023605
\\ ( http://arxiv.org/abs/0902.0107 , 394kb)
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Till next time,
Matt.

--
=========================================================================
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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http://www.physics.uq.edu.au/people/mdavis/matts_arXiv/
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Received on Thu Sep 24 2009 - 15:47:36 EST

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