Matt's arXiv selection: week ending 24 August 2007.

From: Matthew Davis <>
Date: Wed, 29 Aug 2007 11:12:43 +1000 (EST)

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

Hi all,

Thanks for the kind messages after my last email. Last week there were 22 new
papers and 7 replacements.

Date: Fri, 17 Aug 2007 08:00:10 GMT (204kb,D)

Title: Feshbach Molecules in a One-dimensional Optical Lattice
Authors: N. Nygaard, R. Piil and K. Molmer
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We consider a pair of atoms in a one-dimensional optical lattice interacting
via a Feshbach resonance. Using a two-channel description of the resonance,
analytic results for the scattering states inside the continuum band and the
discrete bound states outside the band are derived. In addition, we suggest
experiments to probe and utilize the properties of the system, either by
resonantly driven transitions or by sweeping the resonance state through the
Bloch band of scattering states by varying an applied magnetic field.
\\ ( , 204kb)
Date: Fri, 17 Aug 2007 18:31:19 GMT (39kb)

Title: Flow and critical velocity of an imbalanced Fermi gas through an optical
Authors: J. Tempere
Categories: cond-mat.supr-con
Comments: 8 pages, 1 figure, contribution for the QFS 2007 conference
   Optical lattices offer the possibility to investigate the superfluid
properties of both Bose condensates and Fermionic superfluid gases. When a
population imbalance is present in a Fermi mixture, this leads to frustration
of the pairing, and the superfluid properties will be affected. In this
contribution, the influence of imbalance on the flow of a Fermi superfluid
through an optical lattice is investigated. The flow through the lattice is
analysed by taking into account coupling between neighbouring layers of the
optical lattice up to second order in the interlayer tunneling amplitude for
single atoms. The critical velocity of flow through the lattice is shown to
decrease monotonically to zero as the imbalance is increased to 100%.
Closed-form analytical expressions are given for the tunneling contribution to
the action and for the critical velocity as a function of the binding energy of
pairs in the (quasi) two-dimensional Fermi superfluid and as a function of the
\\ ( , 39kb)
Date: Mon, 20 Aug 2007 14:08:28 GMT (213kb)

Title: Migration of bosonic particles across a Mott insulator to superfluid
   phase interface
Authors: Michael J. Hartmann and Martin B. Plenio
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 5 pages, 6 figures
   We consider a boundary between a Mott insulator and a superfluid region of a
Bose-Hubbard model at unit filling. Initially both regions are decoupled and
cooled to their respective ground states. We show that, after switching on a
small tunneling rate between both regions, all particles of the Mott region
migrate to the superfluid area. This migration takes place whenever the
difference between the chemical potentials of both regions is less than the
maximal energy of any eigenmode of the superfluid. We verify our results
numerically with DMRG simulations and explain them analytically with a master
equation approximation, finding good agreement between both approaches. Finally
we carry out a feasibility study for the observation of the effect in coupled
arrays of micro-cavities and optical lattices.
\\ ( , 213kb)
Date: Mon, 20 Aug 2007 19:25:10 GMT (81kb)

Title: Three-State Feshbach Resonances Mediated By Second-Order Couplings
Authors: Christopher J. Hemming, Roman V. Krems
Categories: physics.atom-ph physics.chem-ph
Comments: 27 pages, 4 figures
   We present an analytical study of three-state Feshbach resonances induced by
second-order couplings. Such resonances arise when the scattering amplitude is
modified by the interaction with a bound state that is not directly coupled to
the scattering state containing incoming flux. Coupling occurs indirectly
through an intermediate state. We consider two problems: (i) the intermediate
state is a scattering state in a distinct open channel; (ii) the intermediate
state is an off-resonant bound state in a distinct closed channel. The first
problem is a model of electric-field-induced resonances in ultracold collisions
of alkali metal atoms [Phys. Rev. A 75, 032709 (2007)] and the second problem
is relevant for ultracold collisions of complex polyatomic molecules, chemical
reaction dynamics, photoassociation of ultracold atoms, and electron - molecule
scattering. Our analysis yields general expressions for the energy dependence
of the T-matrix elements modified by three-state resonances and the dependence
of the resonance positions and widths on coupling amplitudes for the
weak-coupling limit. We show that the second problem can be generalized to
describe resonances induced by indirect coupling through an arbitrary number of
sequentially coupled off-resonant bound states and analyze the dependence of
the resonance width on the number of the intermediate states.
\\ ( , 81kb)
Date: Tue, 21 Aug 2007 16:42:54 GMT (359kb)

Title: Universal properties of a trapped two-component Fermi gas at unitarity
Authors: D. Blume, J. von Stecher and Chris H. Greene
Categories: cond-mat.other
Comments: 4+ pages, 2 Figs., 2 Tables
   We treat the trapped two-component Fermi system, in which unlike fermions
interact through a two-body short-range potential having no bound state but an
infinite scattering length. By accurately solving the Schroedinger equation for
up to N=6 fermions, we show that no many-body bound states exist other than
those bound by the trapping potential, and we demonstrate unique universal
properties of the system: Certain excitation frequencies are separated by
$2\hbar\omega$, the wavefunctions agree with analytical predictions and a
virial theorem is fulfilled. Further calculations up to N=30 determine the
excitation gap, an experimentally accessible universal quantity, and it agrees
with recent predictions based on a density functional approach.
\\ ( , 359kb)
Date: Tue, 21 Aug 2007 09:05:44 GMT (17kb)

Title: Collective excitations of trapped one-dimensional dipolar quantum gases
Authors: P. Pedri (Orsay), S. De Palo (Trieste), E. Orignac (ENS-Lyon), R.
   Citro (Salerno), M. L. Chiofalo (SNS Pisa)
Categories: cond-mat.other cond-mat.str-el
Comments: 5 pages, 2 EPS figures, RevTeX 4
   We calculate the excitation modes of a 1D dipolar quantum gas confined in a
harmonic trap with frequency $\omega_0$ and predict how the frequency of the
breathing n=2 mode characterizes the interaction strength evolving from the
Tonks-Girardeau value $\omega_2=2\omega_0$ to the quasi-ordered, super-strongly
interacting value $\omega_2=\sqrt{5}\omega_0$. Our predictions are obtained
within a hydrodynamic Luttinger-Liquid theory after applying the Local Density
Approximation to the equation of state for the homogeneous dipolar gas, which
are in turn determined from Reptation Quantum Monte Carlo simulations. They are
shown to be in quite accurate agreement with the results of a sum-rule
approach. These effects can be observed in current experiments, revealing the
Luttinger-liquid nature of 1D dipolar Bose gases.
\\ ( , 17kb)
Date: Tue, 21 Aug 2007 13:54:35 GMT (277kb)

Title: Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a
   harmonic trap
Authors: C. Klempt, T. Henninger, O. Topic, J. Will, St. Falke, W. Ertmer, and
   J. Arlt
Categories: cond-mat.other
Comments: 7 pages, 8 figures
   We report on the transport of mixed quantum degenerate gases of bosonic 87Rb
and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The
samples are transported over a distance of 6 mm to the geometric center of the
anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented
by a small modification of the QUIC trap and is free of losses and heating. It
allows all experiments using QUIC traps to use the highly homogeneous magnetic
fields that can be created in the center of a QUIC trap and improves the
optical access to the atoms, e.g., for experiments with optical lattices. This
mechanism may be cascaded to cover even larger distances for applications with
quantum degenerate samples.
\\ ( , 277kb)
Date: Mon, 20 Aug 2007 20:46:42 GMT (846kb)

Title: Magnetic Field Estimation Beyond 1/N Scaling
Authors: Heather L. Partner, Brigette D. Black, and JM Geremia
Categories: quant-ph
Comments: 4 pages, 3 figures
   We propose an atomic magnetometer for which the field estimation uncertainty
decreases faster than 1/N with the number of atoms N. Our procedure estimates
the magnetic field by observing an optical probe field that is multi-passed
through the atomic system during Larmor precession.
\\ ( , 846kb)
Date: Tue, 21 Aug 2007 13:22:43 GMT (415kb,D)

Title: The Physics of Information
Authors: F. Alexander Bais and J. Doyne Farmer
Categories: physics.class-ph cond-mat.stat-mech gr-qc physics.gen-ph quant-ph
Comments: The paper has 64 pages and 9 figures. It is a contribution to "The
   handbook on the philosophy of information", edited by J. van Benthem and P.
   Adriaans, to be published by Elsevier
Report-no: ITFA-2007-37 and SFI Working paper
   We review of the interface between (theoretical) physics and information for
non-experts. The origin of information as related to the notion of entropy is
described, first in the context of thermodynamics then in the context of
statistical mechanics. A close examination of the foundations of statistical
mechanics and the need to reconcile the probabilistic and deterministic views
of the world leads us to a discussion of chaotic dynamics, where information
plays a crucial role in quantifying predictability. We then discuss a variety
of fundamental issues that emerge in defining information and how one must
exercise care in discussing concepts such as order, disorder, and incomplete
knowledge. We also discuss an alternative form of entropy and its possible
relevance for nonequilibrium thermodynamics.
   In the final part of the paper we discuss how quantum mechanics gives rise to
the very different concept of quantum information. Entirely new possibilities
for information storage and computation are possible due to the massive
parallel processing inherent in quantum mechanics. We also point out how
entropy can be extended to apply to quantum mechanics to provide a useful
measurement for quantum entanglement.
   Finally we make a small excursion to the interface betweeen quantum theory
and general relativity, where one is confronted with an "ultimate information
paradox" posed by the physics of Black Holes.
   In this review we have limited ourselves; not all relevant topics that touch
on physics and information could be covered.
\\ ( , 415kb)
Date: Tue, 21 Aug 2007 08:54:18 GMT (2kb)

Title: Comment on "Direct Observation of Second Order Atom Tunnelling"
Authors: V.A. Kuz'menko
Categories: physics.optics physics.atom-ph
Comments: 2 pages
   In recent article (arXiv:0707.3985) S. Foelling, at al. study atom tunnelling
in optical lattice. We point out here, that before the tunnelling study in
optical lattice authors must prove the concept of polarization interaction of
atoms with optical lattice and disprove the concept of inequality of forward
and reversed processes in optics.
\\ ( , 2kb)
Date: Wed, 22 Aug 2007 08:49:42 GMT (17kb)

Title: Entanglement Entropy in Extended Quantum Systems
Authors: John Cardy
Categories: cond-mat.stat-mech
Comments: 6 pages. Plenary talk delivered at Statphys 23, Genoa, July 2007
   After a brief introduction to the concept of entanglement in quantum systems,
I apply these ideas to many-body systems and show that the von Neumann entropy
is an effective way of characterising the entanglement between the degrees of
freedom in different regions of space. Close to a quantum phase transition it
has universal features which serve as a diagnostic of such phenomena. In the
second part I consider the unitary time evolution of such systems following a
`quantum quench' in which a parameter in the hamiltonian is suddenly changed,
and argue that finite regions should effectively thermalise at late times,
after interesting transient effects.
\\ ( , 17kb)
Date: Wed, 22 Aug 2007 15:44:39 GMT (274kb)

Title: Exact Solution of Strongly Interacting Quasi One-Dimensional Spinor Bose
Authors: Frank Deuretzbacher, Klaus Fredenhagen, Daniel Becker, Kai Bongs,
   Klaus Sengstock, Daniela Pfannkuche
Categories: cond-mat.other
Comments: 4 pages, 3 figures
   We present an analytically exact solution of the fundamental system of quasi
one-dimensional bosons with infinite delta-interaction and arbitrary spin. The
wave functions are constructed from the wave functions of non-interacting
spinless fermions, based on Girardeau's Fermi-Bose mapping, and the degeneracy
of the energy levels is determined. Our mapping constitutes a one-to-one
correspondence between spin wave functions of distinguishable particles and the
ground states of spinor bosons. In addition, we calculate spin densities and
momentum distributions of the degenerate ground states as the most important
measurable quantities of these systems.
\\ ( , 274kb)
Date: Wed, 22 Aug 2007 19:08:23 GMT (533kb)

Title: Evidence for Metallic Behavior in an Atomic Bose-Hubbard System
Authors: D. McKay, M. White, M. Pasienski, and B. DeMarco
Categories: cond-mat.other
Comments: 13 pages, 4 figures; new version forthcoming
   We have observed a metallic-like state, which persists to the
zero-temperature limit, in a 3D Bose-Hubbard system of ultra-cold atoms trapped
in an optical lattice. The damping rate of atomic motion--the analog of
electrical resistance in a solid--in the confining parabolic potential fits
well to a model that includes finite damping at zero temperature. The
low-temperature behavior is consistent with the theory of quantum tunneling of
phase slips, while at higher temperatures a cross-over consistent with the
transition between quantum tunneling and thermal activation of phase slips is
evident. The existence of a metallic phase in a bosonic system may have
implications for the unusual dissipative phases apparent in solid-state
superconducting films.
\\ ( , 533kb)
Date: Wed, 22 Aug 2007 06:30:34 GMT (163kb)

Title: Tripartite entanglement and threshold properties of coupled intracavity
   downconversion and sum-frequency generation
Authors: C. Pennarun, A.S. Bradley, and M.K. Olsen
Categories: quant-ph
Comments: 24 pages, 15 figures
   The process of cascaded downconversion and sum-frequency generation inside an
optical cavity has been predicted to be a potential source of three-mode
continuous-variable entanglement. When the cavity is pumped by two fields, the
threshold properties have been analysed, showing that these are more
complicated than in well-known processes such as optical parametric
oscillation. When there is only a single pumping field, the entanglement
properties have been calculated using a linearised fluctuation analysis, but
without any consideration of the threshold properties or critical operating
points of the system. In this work we extend this analysis to demonstrate that
the singly pumped system demonstrates a rich range of threshold behaviour when
quantisation of the pump field is taken into account and that asymmetric
polychromatic entanglement is available over a wide range of operational
\\ ( , 163kb)
Date: Wed, 22 Aug 2007 16:27:50 GMT (114kb)

Title: Controlling the Ratchet Effect for Cold Atoms
Authors: Anatole Kenfack, and Arjendu K. Pattanayak
Categories: quant-ph
Comments: 4 pages, 4 figures
   Quantum resonances manifested by directed currents have been realised with
cold atoms subject to a flashing asymmetric potential. In this Hamiltonian
system, we show that by controling the potential strength, higher-order quantum
resonances emerge, some of them exhibiting reversals and others transporting a
lot better than simpler resonances. We consider the emergence of these
resonances in terms of the Floquet bands and show that they are only observed
in the full classically chaotic regime. These phenomena should readily be
observed in experiments.
\\ ( , 114kb)
Date: Tue, 21 Aug 2007 21:09:48 GMT (277kb)

Title: Recombination fluorescence in ultracold neutral plasmas
Authors: S. D. Bergeson and F. Robicheaux
Categories: physics.atom-ph physics.plasm-ph
   We present the first measurements and simulations of recombination
fluorescence in ultracold neutral plasmas. In contrast with previous work,
experiment and simulation are in significant disagreement. Comparison with a
recombination model suggests that the disagreement could be due to the high
energy portion of the electron energy distribution or to large energy changes
in electron/Rydberg scattering. Recombination fluorescence opens a new
diagnostic window in ultracold plasmas because it probes the deeply-bound
Rydberg levels, which depend critically on electron energetics.
\\ ( , 277kb)
Date: Wed, 22 Aug 2007 20:00:12 GMT (52kb)

Title: Supersolid and devil's staircase of hardcore bosons on anisotropic
   triangular lattice
Authors: Sergei V. Isakov, Hong-Chi Chien, Jian-Jheng Wu, Yung-Chung Chen,
   Chung-Hou Chung, Krishnendu Sengupta and Yong Baek Kim
Categories: cond-mat.str-el cond-mat.mes-hall
Comments: 5 pages, 5 figures
   We present quantum and variational Monte Carlo results of the hardcore boson
model with anisotropic nearest-neighbor hopping and repulsive interactions on
triangular lattice. It is shown that there exist a series of first order
transitions between different supersolid phases as the anisotropy parameter is
changed. The ordering wavevectors of these phases are locked to commensurate
values and jump between adjacent supersolid phases. We conjecture that the
ordering wavevectors may exhibit a complete devil's staircase pattern in the
thermodynamic limit.
\\ ( , 52kb)
Date: Thu, 23 Aug 2007 07:13:16 GMT (171kb)

Title: Casimir Forces in Trapped Dilute Bose Gas Between Two Slabs
Authors: Xiao-Lu Yu, Ran Qi, Z.B. Li, W. M. Liu
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We discuss a Casimir force due to zero-temperature quantum fluctuations in a
weakly interacting Bose-Einstein condensate (BEC) with a strong harmonic trap.
The results show that the presence of a strong harmonic trap changes the power
law behavior of Casimir force due to the dimensional reduction effect. At
finite temperature, we calculate Casimir force due to thermal fluctuation and
find an exotic temperature dependent behavior in the first order term. Finally,
we speculate some possible experimental realization and detection of the force
in future experiments.
\\ ( , 171kb)
Date: Thu, 23 Aug 2007 11:34:37 GMT (127kb)

Title: Ground State Properties of an Asymmetric Hubbard Model for Unbalanced
   Ultracold Fermionic Quantum Gases
Authors: T. Gottwald and P. G. J. van Dongen
Categories: cond-mat.str-el
Comments: 9 pages, 5 figures
   In order to describe unbalanced ultracold fermionic quantum gases on optical
lattices in a harmonic trap, we investigate an attractive ($U<0$) asymmetric
($t_\uparrow\neq t_\downarrow$) Hubbard model with a Zeeman-like magnetic
field. In view of the model's spatial inhomogeneity, we focus in this paper on
the solution at Hartree-Fock level. The Hartree-Fock Hamiltonian is
diagonalized with particular emphasis on superfluid phases. For the special
case of spin-independent hopping we analytically determine the number of
solutions of the resulting self-consistency equations and the nature of the
possible ground states at weak coupling. Numerical results for unbalanced
Fermi-mixtures are presented within the local density approximation. In
particular, we find a fascinating shell structure, involving normal and
superfluid phases. For the general case of spin-dependent hopping we calculate
the density of states and the possible superfluid phases in the ground state.
In particular, we find a new magnetized superfluid phase.
\\ ( , 127kb)
Date: Thu, 23 Aug 2007 14:29:48 GMT (229kb)

Title: Asymmetric Fermi superfluid with different atomic species in a harmonic
Authors: C.-H. Pao, shin-Tza Wu, and S.-K. Yip
Categories: cond-mat.supr-con cond-mat.other
Comments: 12 pages, 7 figures
   We study the dilute fermion gas with pairing between two species and unequal
concentrations in a harmonic trap using the mean field theory and the local
density approximation. We found that the system can exhibit a superfluid shell
structure sandwiched by the normal fermions. This superfluid shell structure
occurs if the mass ratio is larger then certain critical value which increases
from the weak-coupling BCS region to the strong-coupling BEC side. In the
strong coupling BEC regime, the radii of superfluid phase are less sensitive to
the mass ratios and are similar to the case of pairing with equal masses.
However, the lighter leftover fermions are easier to mix with the superfluid
core than the heavier ones. A partially polarized superfluid can be found if
the majority fermions are lighter, whereas phase separation is still found if
they are heavier.
\\ ( , 229kb)
Date: Thu, 23 Aug 2007 13:50:59 GMT (84kb)

Title: Phase diagram of a Bose-Fermi mixture in a one-dimensional optical
   lattice in terms of fidelity and entanglement
Authors: Wen-Qiang Ning, Shi-Jian Gu, Chang-Qin Wu and Hai-Qing Lin
Categories: cond-mat.str-el
Comments: 4 pages 3 figures
   We study the ground-state phase diagram of a Bose-Fermi mixture loaded in a
one-dimensional optical lattice by computing the ground-state fidelity and
quantum entanglement. We find that the fidelity is able to signal quantum phase
transitions between the Luttinger liquid phase, the density-wave phase, and the
phase separation state of the system; and the concurrence can be used to signal
the transition between the density-wave phase and the Ising phase.
\\ ( , 84kb)
Date: Thu, 23 Aug 2007 19:43:42 GMT (49kb,D)

Title: Flux locking a superfluid interferometer
Authors: Yuki Sato, Aditya Joshi and Richard Packard
Categories: cond-mat.other
Comments: 3 pages, 2 figures
Journal-ref: Y. Sato, A. Joshi, and R. Packard, Appl. Phys. Lett. 91, 074107
DOI: 10.1063/1.2772659
   We demonstrate a flux locking technique using injected heat current to
linearize the output of a superfluid helium-4 interferometer. A rotation flux
through the interferometer loop produces a shift in the phase of the superfluid
order parameter. This shift is nullified via negative feedback by a phase-shift
caused by the injected heat current. The feedback signal is then a linear
function of rotation flux.
\\ ( , 49kb)

The replacements:

replaced with revised version Mon, 20 Aug 2007 17:40:42 GMT (128kb)

Title: Transport behaviour of a Bose Einstein condensate in a bichromatic
   optical lattice
Authors: Aranya B Bhattacherjee and Monika Pietrzyk
Categories: cond-mat.stat-mech
Comments: Modified manuscript
\\ ( , 128kb)
replaced with revised version Mon, 20 Aug 2007 18:31:32 GMT (152kb)

Title: Superfluid-insulator transitions of the Fermi gas with near-unitary
   interactions in a periodic potential
Authors: Eun Gook Moon, Predrag Nikolic and Subir Sachdev
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 5 pages, 3 figures
\\ ( , 152kb)
replaced with revised version Tue, 21 Aug 2007 16:48:43 GMT (151kb)

Title: Dynamics of a strongly interacting Fermi gas: the radial quadrupole mode
Authors: A. Altmeyer (1), S. Riedl (1 and 2), M. J. Wright (1), C. Kohstall
   (1), J. Hecker Denschlag (1) and R. Grimm (1 and 2) ((1) Inst. of
   Experimental Physics and Center for Quantum Physics, Univ. Innsbruck,
   Technikerstra{\ss}e 25, Austria, (2) Inst. for Quantum Optics and Quantum
   Information, Acad. of Sciences, Austria)
Categories: cond-mat.other
Comments: 11 pages, 11 figures v2: minor changes
\\ ( , 151kb)
replaced with revised version Mon, 20 Aug 2007 22:38:06 GMT (881kb)

Title: Ultracold Rydberg Atoms in a Ioffe-Pritchard Trap
Authors: Bernd Hezel, Igor Lesanovsky, Peter Schmelcher
Categories: physics.atom-ph
Comments: 30 pages, 10 figures, added references, substantiation of
\\ ( , 881kb)
replaced with revised version Thu, 23 Aug 2007 00:09:12 GMT (571kb)

Title: Ultracold Bosons in a Tilted Multi-level Double-Well Potential
Authors: D. R. Dounas-Frazer, A. M. Hermundstad and L. D. Carr
Categories: quant-ph cond-mat.other
Comments: 4 pages, 3 figures
\\ ( , 571kb)
replaced with revised version Thu, 23 Aug 2007 17:00:18 GMT (279kb)

Title: Spectrum and Dynamics of the BCS-BEC crossover from a few-body
Authors: Javier von Stecher, Chris H. Greene
Categories: cond-mat.supr-con nucl-th physics.atom-ph quant-ph
Comments: 4 pages, final version to appear in PRL
\\ ( , 279kb)
replaced with revised version Thu, 23 Aug 2007 11:21:11 GMT (17kb)

Title: Pairing based cooling of Fermi gases
Authors: M. J. Leskinen, J. Kinnunen, P. Torma
Categories: cond-mat.other cond-mat.supr-con
Comments: Journal version 4 pages, 4 figures
Report-no: NSF-KITP-07-101
Journal-ref: Phys. Rev. A 76, 021604(R) 2007
\\ ( , 17kb)

Till next time,

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
Matt's arXiv selection: weekly summary of cold-atom papers from
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Received on Wed Aug 29 2007 - 11:12:43 EST

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