Matt's arXiv selection: week ending 30 January 2009

From: Matthew Davis <>
Date: Fri, 17 Apr 2009 11:25:12 +1000

The following message was sent to the matts_arxiv list by Matthew Davis <>

No, you don't have a problem with your email. I really am 10 weeks behind. My
current batch of lectures ends shortly and I hope to catch up soon. There
doesn't seem to be much point in doing this if it is so late! :)

There are 39 new preprints and 11 replacements in this message.

Date: Thu, 22 Jan 2009 21:02:25 GMT (672kb)

Title: Density-Wave and Antiferromagnetic States of Fermionic Atoms in Optical
Authors: Takuji Higashiyama, Kensuke Inaba, Sei-ichiro Suga
Categories: cond-mat.other cond-mat.supr-con
Comments: 7 pages, 7 figures
   We study the two-band effects on ultracold fermionic atoms in optical
lattices by means of dynamical mean-field theory. We find that at half-filling
the atomic-density-wave (ADW) state emerges owing to the two-band effects in
the attractive interaction region, while the antiferromagnetic state appears in
the repulsive interaction region. As the orbital splitting is increased, the
quantum phase transitions from the ADW state to the superfluid state and from
the antiferromagnetic state to the metallic state occur in respective regions.
Systematically changing the orbital splitting and the interaction, we obtain
the phase diagram at half-filling. The results are discussed using the
effective boson model derived for the strong attractive interaction.
\\ ( , 672kb)
Date: Fri, 23 Jan 2009 09:10:02 GMT (1185kb)

Title: Adiabatic cooling of a tunable Bose-Fermi mixture in an optical lattice
Authors: O. Soe Sorensen, N. Nygaard, P. B. Blakie
Categories: cond-mat.other
Comments: 9 pages, 7 figures
   We consider an atomic Fermi gas confined in a uniform optical lattice
potential, where the atoms can pair into molecules via a magnetic field
controlled narrow Feshbach resonance. Thus by adjusting the magnetic field the
portion of fermionic and bosonic particles in the system can be continuously
varied. We analyze the statistical mechanics of this system and consider the
interplay of the lattice physics with the atom-molecule conversion. We study
the entropic behavior of the system and characterize the temperature changes
that occur during adiabatic ramps across the Feshbach resonance. We show that
an appropriate choice of filling fraction can be used to reduce the system
temperature during such ramps.
\\ ( , 1185kb)
Date: Fri, 23 Jan 2009 13:56:38 GMT (6kb)

Title: Impossibility to describe repulsion with contact interaction
Authors: K. Morawetz, M. Maennel
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 2 pages comment
   Contact interactions always lead to attractive behaviour. Arguments are
presented to show why a repulsive interacting system, e.g. Bose gases, cannot
be described by contact interactions and corresponding treatments are possibly
obscured by the appearance of bound states. The usually used cut-offs are
identified as finite range parameters.
\\ ( , 6kb)
Date: Fri, 23 Jan 2009 19:59:52 GMT (343kb)

Title: Theory of preparation and relaxation of a p-orbital atomic Mott
Authors: John H. Challis, S.M. Girvin, and L.I. Glazman
Categories: cond-mat.other
Comments: 27 pages, 23 figures
   We develop a theoretical framework to understand the preparation and
relaxation of a metastable Mott insulator state within the first excited band
of a 1D optical lattice. The state is loaded by "lifting" atoms from the ground
to the first excited band by means of a stimulated Raman transition. We
determine the effect of pulse duration on the accuracy of the state preparation
for the case of a Gaussian pulse shape. Relaxation of the prepared state occurs
in two major stages: double-occupied sites occurring due to quantum
fluctuations initially lead to interband transitions followed by a spreading of
particles in the trap and thermalization. We find the characteristic relaxation
times at the earliest stage and at asymptotically long times approaching
equilibrium. Our theory is applicable to recent experiments performed with 1D
optical lattices [T. M\"uller, S. F\"olling, A. Widera, and I. Bloch, Phys.
Rev. Lett. \textbf{99}, 200405 (2007)].
\\ ( , 343kb)
Date: Fri, 23 Jan 2009 15:49:34 GMT (577kb)

Title: Controlling spin current in a trapped Fermi gas
Authors: X. Du, Y. Zhang, J. Petricka, and J. E. Thomas
Categories: cond-mat.other
Comments: 4 pages, 3 figures
   We observe fundamental new features of spin current in a weakly interacting
Fermi gas of $^6$Li. By creating a spin current and then reversing its flow, we
demonstrate control of the spin current. This reversal is predicted by an
undamped spin wave theory, which we have developed to explain our previous
observation of spin segregation in a trapped Fermi gas. Numerical calculations
based on this theory are in very good agreement with the experimental results
both in amplitude and temporal evolution. The theory provides a simple physical
description of the origin of the spin current and suggests that broad control
of the spin current is possible.
\\ ( , 577kb)
Date: Fri, 23 Jan 2009 20:11:23 GMT (688kb)

Title: Transcritical flow of a Bose-Einstein condensate through a penetrable
Authors: A.M. Leszczyszyn, G.A. El, Yu.G. Gladush, A.M. Kamchatnov
Categories: cond-mat.other
Comments: 21 pages, 17 figures
   The problem of the transcritical flow of a Bose-Einstein condensate through a
wide repulsive penetrable barrier is studied analytically using the combination
of the localized "hydraulic" solution of the 1D Gross-Pitaevskii equation and
the solutions of the Whitham modulation equations describing the resolution of
the upstream and downstream discontinuities through dispersive shocks. It is
shown that within the physically reasonable range of parameters the downstream
dispersive shock is attached to the barrier and effectively represents the
train of very slow dark solitons, which can be observed in experiments. The
rate of the soliton emission, the amplitudes of the solitons in the train and
the drag force are determined in terms of the BEC oncoming flow velocity and
the strength of the potential barrier. Excellent agreement with direct
numerical solution is demonstrated. Connection with recent experiments is
\\ ( , 688kb)
Date: Fri, 23 Jan 2009 20:16:11 GMT (302kb,D)

Title: Three component fermions pairing in two dimensions
Authors: Theja N. De Silva
Categories: cond-mat.other
Comments: 5 pages and 5figures
   We study paring of interacting three component Fermi gases in two dimensions.
By using a mean field theory to decouple the interactions between different
components, we study the free energy landscapes as a function of various
parameters including chemical potentials, binding energies (interactions), and
temperature. We find series of second order thermal phase transitions and
series of first order quantum phase transitions for a homogenous system as we
change the parameters. In particular, we find the simultaneous existence of
three superfluid phases as well as re-entrant quantum phase transitions as we
tune the parameters appropriately.
\\ ( , 302kb)
Date: Fri, 23 Jan 2009 11:18:58 GMT (327kb)

Title: Ultra-low noise microwave generation with fiber-based optical frequency
   comb and application to atomic fountain clock
Authors: J. Millo, M. Abgrall, M. Lours, E.M.L. English, H. Jiang, J. Guena, A.
   Clairon, S. Bize, Y. Le Coq, G. Santarelli, M.E. Tobar
Categories: physics.atom-ph physics.optics
Comments: 3 pages, 3 figures
   We demonstrate the use of a fiber-based femtosecond laser locked onto an
ultra-stable optical cavity to generate a low-noise microwave reference signal.
Comparison with both a liquid Helium cryogenic sapphire oscillator (CSO) and a
Ti:Sapphire-based optical frequency comb system exhibit a stability about
$3\times10^{-15}$ between 1 s and 10 s. The microwave signal from the fiber
system is used to perform Ramsey spectroscopy in a state-of-the-art Cesium
fountain clock. The resulting clock system is compared to the CSO and exhibits
a stability of $3.5\times10^{-14}\tau^{-1/2}$. Our continuously operated
fiber-based system therefore demonstrates its potential to replace the CSO for
atomic clocks with high stability in both the optical and microwave domain,
most particularly for operational primary frequency standards.
\\ ( , 327kb)
Date: Sat, 24 Jan 2009 00:08:29 GMT (340kb)

Title: Crystalline Magnetic Order in a Dipolar Quantum Fluid
Authors: M. Vengalattore, J. Guzman, S. Leslie, F. Serwane, D. M. Stamper-Kurn
Categories: cond-mat.other
   We report on the magnetic phases of quasi-two dimensional $^{87}$Rb F=1
spinor gases produced by cooling unmagnetized gases into the regime of quantum
degeneracy. We find a robust low temperature magnetic phase characterized by
crystalline ordering of spin domains, an instance of spontaneously broken
translational symmetry in a quantum fluid. This phase displays an emergent
order parameter, a spin axis along which the magnetization shows the largest
\\ ( , 340kb)
Date: Fri, 23 Jan 2009 09:09:38 GMT (926kb)

Title: Observation of prolonged coherence time of the collective spin wave of
   atomic ensemble in a paraffin coated Rb vapor cell
Authors: Shuo Jiang, Xiao-Ming Luo, Li-Qing Chen, Po-Ning, Shuai Chen,
   Jing-Yang Wang, Zhi-Ping Zhong and Jian-Wei Pan
Categories: quant-ph
Comments: 4 pages, 4 figures
   We report a prolonged coherence time of the collective spin wave of a thermal
87Rb atomic ensemble in a paraffin coated cell. The spin wave is prepared
through a stimulated Raman Process. The long coherence time time is achieved by
prolonging the lifetime of the spins with paraffin coating and minimize
dephasing with optimal experimental configuration. The observation of the long
time delayed-stimulated Stokes signal in the writing process suggests the
prolonged lifetime of the prepared spins; a direct measurement of the decay of
anti-Stokes signal in the reading process shows the coherence time is up to 300
us after minimizing dephasing. This is one hundred times longer than the
reported coherence time in the similar experiments in thermal atomic ensembles
based on the Duan-Lukin-Cirac-Zoller (DLCZ) and its improved protocols. This
prolonged coherence time sets the upper limit of the memory time in quantum
repeaters based on such protocols, which is crucial for the realization of
long-distance quantum communication. The previous reported fluorescence
background in the writing process due to collision in a sample cell with buffer
gas is also reduced in a cell without buffer gas.
\\ ( , 926kb)
Date: Sat, 24 Jan 2009 00:08:29 GMT (340kb)

Title: Crystalline Magnetic Order in a Dipolar Quantum Fluid
Authors: M. Vengalattore, J. Guzman, S. Leslie, F. Serwane, D. M. Stamper-Kurn
Categories: cond-mat.other
   We report on the magnetic phases of quasi-two dimensional $^{87}$Rb F=1
spinor gases produced by cooling unmagnetized gases into the regime of quantum
degeneracy. We find a robust low temperature magnetic phase characterized by
crystalline ordering of spin domains, an instance of spontaneously broken
translational symmetry in a quantum fluid. This phase displays an emergent
order parameter, a spin axis along which the magnetization shows the largest
\\ ( , 340kb)
Date: Sat, 24 Jan 2009 16:57:42 GMT (29kb)

Title: Ultracold molecules: new probes on the variation of fundamental
Authors: Cheng Chin, V.V. Flambaum, K.G. Kozlov
Categories: cond-mat.other
   Ultracold molecules offer brand new opportunities to probe the variation of
fundamental constants with unprecedented sensitivity. This paper summarizes
theoretical background and current constraints on the variation of fine
structure constant and electron-to-proton mass ratio, as well as proposals and
experimental efforts to measure the variations based on ultracold molecules. In
particular, we describe two novel spectroscopic schemes on ultracold molecules
which have greatly enhanced sensitivity to fundamental constants: resonant
scattering near Feshbach resonances and spectroscopy on close-lying energy
levels of ultracold molecules.
\\ ( , 29kb)
Date: Sat, 24 Jan 2009 17:21:23 GMT (260kb)

Title: Efficient scheme for breeding beautiful Schr\"odinger cat in a
   double-well potential
Authors: Gentaro Watanabe
Categories: cond-mat.other
Comments: 4 pages, 6 figures
   For trapped cold Bose gases in a double-well potential, we propose a new
scheme for creating the Schr\"odinger cat state in which all particles in the
right or left wells (so called NOON state). This scheme yields almost perfect
NOON states periodically. In this scheme, the formation time of the NOON state
is drastically reduced by sinusoidally modulating the tunneling matrix element.
For larger number of particles, further reduction is possible using more than
one frequencies. With this scheme, NOON state of larger number of particles can
be realized in current experiments.
\\ ( , 260kb)
Date: Sat, 24 Jan 2009 22:53:37 GMT (29kb)

Title: Excitation spectrum and effective interactions of highly-elongated Fermi
Authors: D. Blume, D. Rakshit
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   Full 3D calculations of small two-component Fermi gases under
highly-elongated confinement, in which unlike fermions interact through
short-range potentials with variable atom-atom s-wave scattering length, are
reported. The 3D excitation frequencies are compared with those determined from
atomic and molecular 1D model Hamiltonian. Our numerical results suggest that
the effective 1D atom-dimer and dimer-dimer interactions are to a good
approximation determined by simple analytical expressions. Implications for the
description of quasi-1D Fermi gases within strict 1D frameworks are discussed.
\\ ( , 29kb)
Date: Mon, 26 Jan 2009 19:04:26 GMT (761kb,D)

Title: Topological Insulators and Metals in Atomic Optical Lattices
Authors: Tudor D. Stanescu, Victor Galitski, J.Y. Vaishnav, Charles W. Clark
   and S. Das Sarma
Categories: cond-mat.mes-hall
Comments: 4+ pages, 5 color figures
   We propose the realization of topological quantum states with cold atoms
trapped in an optical lattice. We discuss an experimental setup that generates
a two-dimensional hexagonal lattice in the presence of a light-induced periodic
vector potential, which represents a realization of the Haldane model with cold
atoms. We determine theoretically the conditions necessary for observing the
topological states and show that two of the key conditions are: 1) the
realization of sharp boundaries and 2) the minimization of any smoothly varying
component of the confining potential. We argue that, unlike their condensed
matter counterparts, cold atom topological quantum states can be i) "seen", by
mapping out the characteristic chiral edge states, and ii) controlled, by
controlling the periodic vector potential and the properties of the confining
\\ ( , 761kb)
Date: Mon, 26 Jan 2009 18:16:43 GMT (843kb,D)

Title: Wavepacket dynamics in energy space of a chaotic trimeric Bose-Hubbard
Authors: Moritz Hiller, Tsampikos Kottos, Theo Geisel
Categories: cond-mat.other
Comments: 18 pages, 19 figures
   We study the energy redistribution of interacting bosons in a ring-shaped
quantum trimer as the coupling strength between neighboring sites of the
corresponding Bose-Hubbard Hamiltonian undergoes a sudden change dk. Our
analysis is based on a three-fold approach combining linear response theory
calculations as well as semiclassical and random matrix theory considerations.
The dk-borders of applicability of each of these methods are identified by
direct comparison with the exact quantum mechanical results. We find that while
the variance of the evolving quantum distribution shows a remarkable
quantum-classical correspondence (QCC) for all dk-values, other moments exhibit
this QCC only in the non-perturbative dk-regime.
\\ ( , 843kb)
Date: Fri, 23 Jan 2009 21:36:22 GMT (496kb)

Title: Realistic theory of electromagnetically-induced transparency and slow
   light in a hot vapor of atoms undergoing collisions
Authors: Joyee Ghosh, R. Ghosh, F. Goldfarb, J. L. Le Gou\"et, F. Bretenaker
Categories: quant-ph
   We present a realistic theoretical treatment of a three-level $\Lambda$
system in a hot atomic vapor interacting with a coupling and a probe field of
arbitrary strengths, leading to electromagnetically-induced transparency and
slow light under the two-photon resonance condition. We take into account all
the relevant decoherence processes including col5Blisions. Velocity-changing
collisions (VCCs) are modeled in the strong collision limit effectively, which
helps in achieving optical pumping by the coupling beam across the entire
Doppler profile. The steady-state expressions for the atomic density-matrix
elements are numerically evaluated to yield the experimentally measured
response characteristics. The predictions, taking into account a dynamic rate
of influx of atoms in the two lower levels of the $\Lambda$, are in excellent
agreement with the reported experimental results for $^4$He*. The role played
by the VCC parameter is seen to be distinct from that by the transit time or
Raman coherence decay rate.
\\ ( , 496kb)
Date: Sun, 25 Jan 2009 02:02:57 GMT (753kb)

Title: Regular and chaotic Bose-Einstein condensate in an accelerated
   Wannier-Stark lattice
Authors: Wenhua Hai, Gengbiao Lu, Honghua Zhong
Categories: quant-ph
Comments: 5 pages, 3 figures
   We investigate a Bose-Einstein condensate held in a quasi-one-dimensional
Wannier-Stark lattice which is a combination of linear potential with an
accelerated optical lattice. It is demonstrated that the system can be reduced
to a periodically driven Gross-Pitaevskii one, in which we find the first exact
analytical solution and the regular and chaotic numerical solutions with
accelerated atomic flow densities. The results suggest an experimental scheme
for generating and controlling the accelerating regular and chaotic
\\ ( , 753kb)
Date: Sun, 25 Jan 2009 20:48:35 GMT (1205kb,D)

Title: Global operations for protected quantum memories in atomic spin lattices
Authors: G.K. Brennen, K. Hammerer, L. Jiang, M. D. Lukin, and P. Zoller
Categories: quant-ph
Comments: 16 pages, 6 figures
   Quantum information processed in strongly correlated states of matter can
provide built in hardware protection against errors. We may encode information
in highly non local degrees of freedom, such as using three dimensional spin
lattices for subsystem codes or two dimensional spin lattices for topologically
ordered surface codes and measurement based codes. Recently, in [L. Jiang et
al., Nature Physics {\bf 4}, 482 (2008)] the authors showed how to manipulate
these global degrees of freedom using optical lattices coupled to a bosonic
degree of freedom via a cavity. We elaborate on these ideas and recapitulate
two approaches to implement many body gates necessary for quantum information
processing, both relying on controlled interactions of an ancillary cavity mode
with the spin system and single ancilla particles. The main focus of the
present paper is to analyze the effect of imperfections such a cavity decay and
collective and individual spin decoherence. We present strategies to fight
decoherence by monitoring cavity decay and show that high gate fidelities can
be achieved in the strong coupling regime of cavity-QED with state of the art
\\ ( , 1205kb)
Date: Mon, 26 Jan 2009 15:58:26 GMT (2068kb,D)

Title: Intensity-field correlation of single-atom resonance fluorescence
Authors: S. Gerber, D. Rotter, L. Slodicka, J. Eschner, H. J. Carmichae, and R.
Categories: quant-ph
Comments: 4 pages, 4 figures
   We report measurements of an intensity-field correlation function of the
resonance fluorescence of a single trapped Ba+ ion. Detection of a photon
prepares the atom in its ground state and we observe its subsequent evolution
under interaction with a laser field of well defined phase. We record the
regression of the resonance fluorescence source field. This provides a direct
measurement of the field of the radiating dipole of a single atom and exhibits
its strong non-classical behavior. In the experimental setup an interference
measurement is conditioned on a fluorescence photon detection. The third-order
correlation function thus recorded demonstrates an aspect of wave-particle
duality at the single-atom, single-photon level.
\\ ( , 2068kb)
Date: Mon, 26 Jan 2009 14:02:59 GMT (45kb)

Title: Large amplitude spin oscillations in a collisionless trapped atomic gas
Authors: F. Piechon, J.N. Fuchs, and F. Laloe
Categories: physics.atom-ph
   We propose an explanation of the recently observed strong spin segregation in
a trapped Fermi gas by Du et al. Numerical and analytical solutions of a spin
1/2 kinetic equation in a collisionless regime explain quantitatively the
observation of an "anomalous" large time scale and amplitude of the
segregation. The key difference with previous experiment on bosons rests more
in the diluteness of the gas than in the quantum statistics of the atoms. When
they undergo fast ballistic oscillations in the trap, they average the
inhomogeneous external field in an energy dependent way, so that their
transverse spin precession frequency becomes proportional to their energy.
Interactions between atoms of different energies and different spin directions
then involve the identical spin rotation effect (ISRE), which transfers atoms
to the up or down spin state in an energy dependent way. Since low energy atoms
are closer to the center of the trap than high energy atoms, which can visit
its edges, the final outcome is a strong correlation between spins and
\\ ( , 45kb)
Date: Tue, 27 Jan 2009 19:54:34 GMT (1480kb)

Title: Exotic phases and quantum phase transitions: model systems and
Authors: Subir Sachdev
Categories: cond-mat.str-el
Comments: 27 pages, 11 figures; Rapporteur talk at the 24th Solvay Conference
   on Physics, "Quantum Theory of Condensed Matter", Brussels, Oct 2008
   I survey theoretical advances in our understanding of the quantum phases and
phase transitions of Mott insulators, and of allied conducting systems obtained
by doping charge carriers. A number of new experimental examples of Mott
insulators have appeared in recent years, and I critically compare their
observed properties with the theoretical expectations.
\\ ( , 1480kb)
Date: Tue, 27 Jan 2009 17:42:28 GMT (16kb)

Title: Generation of macroscopic singlet states in atomic ensembles
Authors: G\'eza T\'oth, Morgan W. Mitchell
Categories: quant-ph
Comments: 5 pages including 1 figure, revtex4
   We study squeezing of the spin uncertainties by quantum non-demolition (QND)
measurement in non-polarized spin ensembles. Unlike the case of polarized
ensembles, the QND measurements can be performed with negligible back-action
and produce squeezing even in the limit of strong measurement. Together these
allow, in principle, perfect spin squeezing as quantified by [G. Toth et al.,
Phys. Rev. Lett. 99, 250405 (2007)]. The generated spin states approach
many-body singlet states, and contain a macroscopic number of entangled
particles, even when individual spin is large. We estimate the achievable spin
squeezing for achievable experimental parameters. We introduce the Gaussian
treatment of unpolarized spin states.
\\ ( , 16kb)
Date: Tue, 27 Jan 2009 03:00:47 GMT (382kb)

Title: Deceleration of continuous molecular beams
Authors: Eric R. Hudson
Categories: physics.atom-ph physics.chem-ph
   A method for decelerating a continuous beam of neutral polar molecules is
theoretically demonstrated. This method utilizes non-uniform, static electric
fields and regions of adiabatic population transfer to generate a mechanical
force that opposes the molecular beam's velocity. By coupling this technique
with dissipative trap-loading, molecular densities $\geq10^{11}$ cm$^{-3}$ are
possible. When used in combination with forced evaporative cooling the proposed
method may represent a viable route to quantum degeneracy for a wide-class of
molecular species.
\\ ( , 382kb)
Date: Tue, 27 Jan 2009 20:39:03 GMT (338kb)

Title: Measurement of the trapping lifetime close to a cold metallic surface on
   a cryogenic atom-chip
Authors: Andreas Emmert (LKB - Lhomond), Adrian Lupascu (LKB - Lhomond), Gilles
   Nogues (LKB - Lhomond), Michel Brune (LKB - Lhomond), Jean-Michel Raimond
   (LKB - Lhomond), Serge Haroche (LKB - Lhomond, CDF)
Categories: physics.atom-ph
Comments: 5 pages
   We have measured the trapping lifetime of magnetically trapped atoms in a
cryogenic atom-chip experiment. An ultracold atomic cloud is kept at a fixed
distance from a thin gold layer deposited on top of a superconducting trapping
wire. The lifetime is studied as a function of the distances to the surface and
to the wire. Different regimes are observed, where loss rate is determined
either by the technical current noise in the wire or the Johnson-Nyquist noise
in the metallic gold layer, in good agreement with theoretical predictions. Far
from the surface, we observe exceptionally long trapping times for an
atom-chip, in the 10-minutes range.
\\ ( , 338kb)
Date: Mon, 26 Jan 2009 21:00:03 GMT (29kb)

Title: BCS theory of superconductivity: the world's largest Madoff scheme?
Authors: J. E. Hirsch
Categories: physics.gen-ph
   The time-tested BCS theory of superconductivity is generally accepted to be
the correct theory of conventional superconductivity by physicists and, by
extension, by the world at large. In a different realm of human activity, until
very recently Bernard Madoff's time-tested investment operation was generally
accepted as true and legitimate in the financial world. Madoff's Ponzi scheme,
where old investors were being paid off by funds contributed by new investors,
was fundamentally flawed, yet was able to thrive for decades because of many
vested interests. `Red flags' suggesting its illegitimacy were ignored. Here I
suggest that the same is true of BCS theory. There are an increasing number of
`red flags' that strongly suggest the possibility that BCS theory may be
fundamentally flawed. For example, an ever-growing number of superconductors
are being classified as `unconventional', not described by the conventional BCS
theory and each requiring a different physical mechanism. In addition, I argue
that BCS theory is unable to explain the Meissner effect, $the$ most
fundamental property of superconductors. There are several other phenomena in
superconductors for which BCS theory provides no explanation, and BCS theory
has proven unable to predict any new superconducting compounds. From one day to
the next, Madoff's edifice came crashing down and a staggering 50 billion
dollars evaporated, and I suggest that this may also be the fate of BCS theory.
I outline an alternative theory to conventional BCS theory proposed to apply to
all superconductors, `conventional' as well as `unconventional', that offers an
explanation for the Meissner effect as well as for other puzzles and provides
clear guidelines in the search for new high temperature superconductors.
\\ ( , 29kb)
Date: Tue, 27 Jan 2009 22:30:12 GMT (154kb)

Title: Devil's staircases and supersolids in a one-dimensional dipolar Bose gas
Authors: F. J. Burnell, Meera M. Parish, N. R. Cooper, S. L. Sondhi
Categories: cond-mat.other
   We consider a single-component gas of dipolar bosons confined in a
one-dimensional optical lattice, where the dipoles are aligned such that the
long-ranged dipolar interactions are maximally repulsive. In the limit of zero
inter-site hopping and sufficiently large on-site interaction, the phase
diagram is a complete devil's staircase for filling fractions between 0 and 1,
wherein every commensurate state at a rational filling is stable over a finite
interval in chemical potential. We perturb away from this limit in two
experimentally motivated directions involving the addition of hopping and a
reduction of the onsite interaction. The addition of hopping alone yields a
phase diagram, which we compute in perturbation theory in the hopping, where
the commensurate Mott phases now compete with the superfluid. Further softening
of the onsite interaction yields alternative commensurate states with double
occupancies which can form a staircase of their own, as well as one-dimensional
"supersolids" which simultaneously exhibit discrete broken symmetries and
\\ ( , 154kb)
Date: Wed, 28 Jan 2009 01:17:27 GMT (757kb)

Title: Metastable Quantum Phase Transitions in a Periodic One-dimensional Bose
   Gas: Mean-Field and Bogoliubov Analyses
Authors: R. Kanamoto, L. D. Carr, M. Ueda
Categories: cond-mat.other
   We generalize the concept of quantum phase transitions, which is
conventionally defined for a ground state and usually applied in the
thermodynamic limit, to one for \emph{metastable states} in \emph{finite size
systems}. In particular, we treat the one-dimensional Bose gas on a ring in the
presence of both interactions and rotation. To support our study, we bring to
bear mean-field theory, i.e., the nonlinear Schr\"odinger equation, and linear
perturbation or Bogoliubov-de Gennes theory. Both methods give a consistent
result in the weakly interacting regime: there exist \emph{two topologically
distinct quantum phases}. The first is the typical picture of superfluidity in
a Bose-Einstein condensate on a ring: average angular momentum is quantized and
the superflow is uniform. The second is new: one or more dark solitons appear
as stationary states, breaking the symmetry, the average angular momentum
becomes a continuous quantity, and the phase of the condensate can be
continuously wound and unwound.
\\ ( , 757kb)
Date: Wed, 28 Jan 2009 11:30:47 GMT (149kb)

Title: Momentum distribution of a freely expanding Lieb-Liniger gas
Authors: D. Juki\' c, B. Klajn and H. Buljan
Categories: cond-mat.other
   We numerically study free expansion of a few Lieb-Liniger bosons, which are
initially in the ground state of an infinitely deep hard-wall trap. Numerical
calculation is carried out by employing a standard Fourier transform, as
follows from the Fermi-Bose transformation for a time-dependent Lieb-Liniger
gas. We study the evolution of the momentum distribution, the real-space single
particle density, and the occupancies of natural orbitals. We find analytically
(by using the stationary phase approximation) that for sufficiently large times
the shape of the momentum distribution coincides (up to a simple scaling
transformation) with the shape of the real-space single-particle density. This
result is corroborated by our numerical simulations.
\\ ( , 149kb)
Date: Wed, 28 Jan 2009 02:29:43 GMT (200kb,D)

Title: Stochastic Simulations of Conditional Master Equations
Authors: M. R. Hush, A. R. R. Carvalho, J. J. Hope
Categories: quant-ph
Comments: 5 pages, 2 figures
   We demonstrate a technique for performing stochastic simulations of
conditional master equations. This allows first-principles simulations of
continually measured quantum systems, such as those controlled by
measurement-based feedback. We show that the stochastic technique is nearly two
orders of magnitude faster than a Wigner function method by simulating a single
trapped particle undergoing position measurement and feedback control. More
importantly, we demonstrate that the method presented here scales almost
logarithmically with the size of the Hilbert space of the system, allowing
simulations of conditional dynamics of multimode bosonic quantum fields, which
were impractical using previous brute force methods.
\\ ( , 200kb)
Date: Wed, 28 Jan 2009 18:55:57 GMT (263kb)

Title: Preparation of atomic Fock states by trap reduction
Authors: M. Pons, A. del Campo, J. G. Muga, M. G. Raizen
Categories: quant-ph
Comments: 5 pages, 5 figures
   We describe the preparation of atom-number states with strongly interacting
bosons in one dimension, or spin-polarized fermions. The procedure is based on
a combination of weakening and squeezing of the trapping potential. For the
resulting state, the full atom number distribution is obtained. Starting with
an unknown number of particles $N_i$, we optimize the sudden change in the
trapping potential which leads to the Fock state of $N_f$ particles in the
final trap. Non-zero temperature effects as well as different smooth trapping
potentials are analyzed. A simple criterion is provided to ensure the robust
preparation of the Fock state for physically realistic traps.
\\ ( , 263kb)
Date: Wed, 28 Jan 2009 23:40:03 GMT (118kb)

Title: Observation of heteronuclear atomic Efimov resonances
Authors: G. Barontini, C. Weber, F. Rabatti, J. Catani, G. Thalhammer, M.
   Inguscio, F. Minardi
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   The Efimov effect represents a cornerstone in few-body physics. Building on
the recent experimental observation with ultracold atoms, we report the first
experimental signature of Efimov physics in a heteronuclear system. A mixture
of $^{41}$K and $^{87}$Rb atoms was cooled to few hundred nanoKelvins and
stored in an optical dipole trap. Exploiting a broad interspecies Feshbach
resonance, the losses due to three-body collisions were studied as a function
of the interspecies scattering length. We observe an enhancement of the
three-body collisions for three distinct values of the interspecies scattering
lengths, both positive and negative. We attribute the two features at negative
scattering length to the existence of two kind of Efimov trimers, namely KKRb
and KRbRb.
\\ ( , 118kb)
Date: Thu, 29 Jan 2009 06:59:20 GMT (1998kb)

Title: Quantum turbulence: From superfluid helium to atomic Bose-Einstein
Authors: Makoto Tsubota
Categories: cond-mat.other
   This article reviews recent developments in quantum fluid dynamics and
quantum turbulence (QT) for superfluid helium and atomic Bose-Einstein
condensates. Quantum turbulence was discovered in superfluid $^4$He in the
1950s, but the field moved in a new direction starting around the mid 1990s.
Quantum turbulence is comprised of quantized vortices that are definite
topological defects arising from the order parameter appearing in Bose-Einstein
condensation. Hence QT is expected to yield a simpler model of turbulence than
does conventional turbulence. A general introduction to this issue and a brief
review of the basic concepts are followed by a description of vortex lattice
formation in a rotating atomic Bose-Einstein condensate, typical of quantum
fluid dynamics. Then we discuss recent developments in QT of superfluid helium
such as the energy spectra and dissipative mechanisms at low temperatures, QT
created by vibrating structures, and the visualization of QT. As an application
of these ideas, we end with a discussion of QT in atomic Bose-Einstein
\\ ( , 1998kb)
Date: Thu, 29 Jan 2009 05:14:53 GMT (159kb)

Title: Quantifying Finite Temperature Effects in Atom Chip Interferometry of
   Bose-Einstein Condensates
Authors: R.G. Scott, D.A.W. Hutchinson, T.E. Judd, and T.M. Fromhold
Categories: cond-mat.other
Comments: 7 pages, 5 figures
   We quantify the effect of phase fluctuations on atom chip interferometry of
Bose-Einstein condensates. At very low temperatures, we observe small phase
fluctuations, created by mean-field depletion, and a resonant production of
vortices when the two clouds are initially in anti-phase. At higher
temperatures, we show that the thermal occupation of Bogoliubov modes makes
vortex production vary smoothly with the initial relative phase difference
between the two atom clouds. We also propose a technique to observe vortex
formation directly by creating a weak link between the two clouds. The position
and direction of circulation of the vortices is subsequently revealed by kinks
in the interference fringes produced when the two clouds expand into one
another. This procedure may be exploited for precise force measurement or
motion detection.
\\ ( , 159kb)
Date: Thu, 29 Jan 2009 09:34:42 GMT (393kb)

Title: From Bogoliubov's approximation to Popov's hydrodynamic theory: a
   unified picture of superfluidity
Authors: N. Dupuis
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   Using a non-perturbative renormalization-group technique, we compute the
momentum and frequency dependence of the anomalous self-energy and the
one-particle spectral function of two-dimensional interacting bosons at zero
temperature. Below a characteristic momentum scale $k_G$, where the Bogoliubov
approximation breaks down, the anomalous self-energy develops a square root
singularity and the Goldstone mode of the superfluid phase (Bogoliubov sound
mode) coexists with a continuum of excitations, in agreement with the
predictions of Popov's hydrodynamic theory. Thus our results provide a unified
picture of superfluidity in interacting boson systems and connect Bogoliubov's
theory (valid for momenta larger than $k_G$) to Popov's hydrodynamic approach.
\\ ( , 393kb)
Date: Thu, 29 Jan 2009 10:40:33 GMT (133kb)

Title: Stability and pairing in quasi-one-dimensional Bose-Fermi mixtures
Authors: F. M. Marchetti, Th. Jolicoeur, M. M. Parish
Categories: cond-mat.other
Comments: 4 pages, 2 figures
   We consider a mixture of single-component bosonic and fermionic atoms in an
array of coupled one-dimensional "tubes". For an attractive Bose-Fermi
interaction, we show that the system exhibits phase separation instead of the
usual collapse. Moreover, above a critical inter-tube hopping, all first-order
instabilities disappear in both attractive and repulsive mixtures. The
possibility of suppressing instabilities in this system suggests a route
towards the realization of paired phases, including a superfluid of p-wave
pairs unique to the coupled-tube system, and quantum critical phenomena.
\\ ( , 133kb)
Date: Thu, 29 Jan 2009 14:44:18 GMT (1616kb)

Title: Topological Phase in Noncentrosymmetric S-Wave Superfluids of Ultracold
   Fermionic Atoms
Authors: Masatoshi Sato, Yoshiro Takahashi, Satoshi Fujimoto
Categories: cond-mat.supr-con
Comments: 5 pages, 2 figures
   We show that in s-wave superfluids of cold fermionic atoms with laser-field
generated effective spin-orbit interactions, a topological phase with gapless
edge states and Majorana fermion quasiparticles obeying the non-Abelian
statistics is realized in the case with a large population imbalance of two
hyperfine states which form Cooper pairs.
\\ ( , 1616kb)
Date: Thu, 29 Jan 2009 20:30:14 GMT (166kb)

Title: Induced interactions for ultra-cold Fermi gases in optical lattices
Authors: D.-H. Kim, P. Torma, J.-P. Martikainen
Categories: cond-mat.supr-con cond-mat.other
Comments: 4+ pages, 4 figures
   We investigate the effect optical lattices on the BCS superfluidity by using
the Gorkov-Melik-Barkhudarov (GMB) correction to the BCS mean-field theory for
a two-component Fermi gas. We find that the suppression of the order parameter
is strongly enhanced by the lattice effects. The predictions made by the GMB
corrections are in qualitative and, for the cases studied, in quantitative
agreement with previous quantum Monte Carlo results. We discuss how the GMB
correction extends the validity of the mean-field theory to a wider range of
tunable optical lattice systems in different dimensions.
\\ ( , 166kb)
Date: Thu, 29 Jan 2009 16:55:59 GMT (359kb)

Title: Bloch oscillations of Bose-Einstein condensates: Quantum counterpart of
   dynamical instability
Authors: Andrey R. Kolovsky, Hans J\"urgen Korsch, Eva-Maria Graefe
Categories: quant-ph
Comments: 12 pages, 14 figures
   We study the Bloch dynamics of a quasi one-dimensional Bose-Einstein
condensate of cold atoms in a tilted optical lattice modeled by a Hamiltonian
of Bose-Hubbard type: The corresponding mean-field system described by a
discrete nonlinear Schr\"odinger equation can show a dynamical (or modulation)
instability due to chaotic dynamics and equipartition over the quasimomentum
modes. It is shown, that these phenomena are related to a depletion of the
Floquet-Bogoliubov states and a decoherence of the condensate in the
many-particle description. Three different types of dynamics are distinguished:
(i) decaying oscillations in the region of dynamical instability, and (ii)
persisting Bloch oscillations or (iii) periodic decay and revivals in the
region of stability.
\\ ( , 359kb)

The replacements:

replaced with revised version Fri, 23 Jan 2009 17:25:09 GMT (53kb)

Title: Threshold for Chaos and Thermalization in One-Dimensional Mean-Field
   Bose-Hubbard Model
Authors: Amy C. Cassidy, Douglas Mason, Vanja Dunjko, Maxim Olshanii
Categories: cond-mat.other cond-mat.stat-mech
Comments: 4 pages, 3 figures, published version
Journal-ref: Phys. Rev. Lett. 102, 025302 (2009)
DOI: 10.1103/PhysRevLett.102.025302
\\ ( , 53kb)
replaced with revised version Fri, 23 Jan 2009 09:59:09 GMT (1305kb)

Title: Density profiles of polarized Fermi gases confined in harmonic traps
Authors: G. Bertaina and S. Giorgini
Categories: cond-mat.other cond-mat.supr-con
Comments: 6 pages, 4 figures. We added references and modified the figures
Journal-ref: Phys. Rev. A 79, 013616 (2009)
DOI: 10.1103/PhysRevA.79.013616
\\ ( , 1305kb)
replaced with revised version Mon, 26 Jan 2009 08:33:18 GMT (459kb)

Title: Atom chips and one-dimensional Bose gases
Authors: Isabelle Bouchoule (LCFIO), N. J. Van Druten, Christoph I. Westbrook
Categories: physics.atom-ph
\\ ( , 459kb)
replaced with revised version Tue, 27 Jan 2009 16:08:26 GMT (377kb)

Title: Thermodynamics of a trapped unitary Fermi gas
Authors: R. Haussmann and W. Zwerger
Categories: cond-mat.stat-mech
Comments: 10 pages, 5 figures
Report-no: KN-08-05
Journal-ref: Phys. Rev. A 78, 063602 (2008)
\\ ( , 377kb)
replaced with revised version Tue, 27 Jan 2009 11:11:02 GMT (1293kb,D)

Title: Coherent state approach to the cross collisional effects in the
   population dynamics of a two-mode Bose-Einstein condensate
Authors: Thiago F. Viscondi, K. Furuya and M. C. de Oliveira
Categories: quant-ph
Comments: 19 pages, 8 figures. Added some references, remarks on LMG model and
\\ ( , 1293kb)
replaced with revised version Tue, 27 Jan 2009 17:24:57 GMT (233kb)

Title: Negative-index media for matter-wave optics
Authors: J. Baudon, M. Hamamda, J. Grucker, F. Perales, G. Dutier, M. Boustimi
   and M. Ducloy
Categories: quant-ph physics.optics
Comments: 4 pages, 4 figures, submitted at PRL 4 November 2008
\\ ( , 233kb)
replaced with revised version Wed, 28 Jan 2009 03:38:36 GMT (260kb)

Title: Realizing and Detecting the Haldane's Quantum Hall effect with Ultracold
Authors: L. B. Shao, Shi-Liang Zhu, L. Sheng, D. Y. Xing, and Z. D. Wang
Categories: cond-mat.mes-hall
Comments: 5 pages
Journal-ref: Phys. Rev. Lett.101,246810 (2008)
\\ ( , 260kb)
replaced with revised version Wed, 28 Jan 2009 15:18:44 GMT (61kb)

Title: Collective modes of trapped Fermi gases with in-medium interaction
Authors: S.Chiacchiera, T.Lepers, M.Urban, D.Davesne
Categories: cond-mat.other nucl-th
Comments: 17 pages
\\ ( , 61kb)
replaced with revised version Wed, 28 Jan 2009 16:46:40 GMT (653kb)

Title: Kinetic quantum phase transition in bosonic superfluids on a lattice
Authors: A. S. Alexandrov and I. O. Thomas
Categories: cond-mat.other
Comments: 4 pages, 3 figures. Submitted to Physical Review Letters Revised
   version has additional results and a clarification regarding the
   applicability of the values of the hopping parameters
\\ ( , 653kb)
replaced with revised version Thu, 29 Jan 2009 13:42:20 GMT (21kb)

Title: Hubbard model calculations of phase separation in optical lattices
Authors: H. Heiselberg
Categories: cond-mat.supr-con cond-mat.str-el
\\ ( , 21kb)
replaced with revised version Thu, 29 Jan 2009 12:25:21 GMT (77kb)

Title: Generation of nonground-state Bose-Einstein condensates by modulating
   atomic interactions
Authors: E. R. F. Ramos, E. A. L. Henn, J. A. Seman, M. A. Caracanhas, K. M. F.
   Magalh\~aes, K. Helmerson, V. I. Yukalov, V. S. Bagnato
Categories: quant-ph
Comments: 6 pages, 2 figures, 1 table
Journal-ref: Phys. Rev. A 78, 063412 (2008)
DOI: 10.1103/PhysRevA.78.063412
\\ ( , 77kb)

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,        
Matt's arXiv selection: weekly summary of cold-atom papers from
Legal stuff: Unless stated otherwise, this e-mail represents only the
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Received on Fri May 01 2009 - 15:51:04 EST

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