Matt's arXiv selection: week ending 4 April 2008.

From: Matthew Davis <>
Date: Tue, 08 Apr 2008 08:05:36 +1000

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

A total of 40 new preprints and 12 replacements this week.

Date: Thu, 27 Mar 2008 20:26:28 GMT (243kb)

Title: Prospects for cooling nanomechanical motion by coupling to a
   superconducting microwave resonator
Authors: J. D. Teufel, C. A. Regal, K. W. Lehnert
Categories: cond-mat.mes-hall
Comments: 6 pages, 6 figures
   Recent theoretical work has shown that radiation pressure effects can in
principle cool a mechanical degree of freedom to its ground state. In this
paper, we apply this theory to our realization of an opto-mechanical system in
which the motion of mechanical oscillator modulates the resonance frequency of
a superconducting microwave circuit. We present experimental data demonstrating
the large mechanical quality factors possible with metallic, nanomechanical
beams at 20 mK. Further measurements also show damping and cooling effects on
the mechanical oscillator due to the microwave radiation field. These data
motivate the prospects for employing this dynamical backaction technique to
cool a mechanical mode entirely to its quantum ground state.
\\ ( , 243kb)
Date: Fri, 28 Mar 2008 05:54:19 GMT (512kb)

Title: Macroscopic quantum self-trapping in a Bose-Josephson junction with
Authors: S. F. Caballero Benitez, E. A. Ostrovskaya, M. Gulacsi, and Yu. S.
Categories: cond-mat.other
Comments: 8 pages, 8 figures, submitted to PRA
   We study the macroscopic quantum self-trapping effect in a mixture of
Bose-Einstein condensate and a large number of quantum degenerate fermions,
trapped in a double-well potential with a variable separation between the
wells. The large number of fermions localized in each well form quasi-static
impurities that affect the dynamics of the bosonic cloud. Our semi-analytical
analysis based on a mean-field model shows that main features of macroscopic
quantum self trapping in a pure bosonic system are radically modified by the
influence of fermions, with both the onset of self-trapping and properties of
the self-trapped state depending on the fermion concentration as well as on the
type of inter-species interaction. Remarkably, repulsive inter-species
interaction leads to population inversion of the bosonic energy levels in the
trapping potential and hence to the inversion of symmetry of the macroscopic
wavefunction. Realistic physical estimates are given based on experimental
parameters for a $^{40}$K-$^{87}$Rb system.
\\ ( , 512kb)
Date: Fri, 28 Mar 2008 06:30:13 GMT (12kb)

Title: Universal Thermodynamics and Chandrasekhar-Clogston Limit of a Unitary
   Fermi Gas
Authors: Lianyi He and Pengfei Zhuang
Categories: cond-mat.supr-con
Comments: 4 pages
   The critical Zeeman fields and polarization of Fermi superfluidity at
infinite scattering length is studied based on the universality hypothesis.
Taking a general equation of state with some universal coefficients and a
scaling function which can be determined by experiment or Monte Carlo
simulation, we obtain model-independent lower and upper critical fields
$h_{c1}$ and $h_{c2}$ as well as the critical polarization $P_c$. Phase
separation is proven to be the energetically favored ground state between
$h_{c1}$ and $h_{c2}$. Using recent Monte Carlo result of $P_c$, $h_{c1}$ and
$h_{c2}$ are numerically determined.
\\ ( , 12kb)
Date: Fri, 28 Mar 2008 11:16:03 GMT (16kb)

Title: Improving Carnot efficiency with quantum correlations
Authors: Raoul Dillenschneider and Eric Lutz
Categories: cond-mat.stat-mech
Comments: 4 pages, 2 figures
   We consider a quantum Carnot engine that consists of a single-mode radiation
field in a resonating optical cavity. We show that the quantum efficiency can
exceed the classical Carnot limit when the engine is coupled to a reservoir of
thermal entangled two-level atoms. In the limit of small quantum correlations,
we express the Carnot efficiency in terms of the quantum discord, a measure of
nonclassical correlations. We thus establish that quantum correlated states can
be used as a valuable resource in quantum thermodynamics.
\\ ( , 16kb)
Date: Fri, 28 Mar 2008 09:45:31 GMT (788kb)

Title: Collisions between tunable halo dimers: exploring an elementary
   four-body process with identical bosons
Authors: F. Ferlaino, S. Knoop, M. Mark, M. Berninger, H. Sch\"obel, H.-C.
   N\"agerl, and R. Grimm
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We study inelastic collisions in a pure, trapped sample of Feshbach molecules
made of bosonic cesium atoms in the quantum halo regime. We measure the
relaxation rate coefficient for decay to lower-lying molecular states and study
the dependence on scattering length and temperature. We identify a pronounced
loss minimum with varying scattering length along with a further suppression of
loss with decreasing temperature. Our observations provide insight into the
physics of a few-body quantum system that consists of four identical bosons at
large values of the two-body scattering length.
\\ ( , 788kb)
Date: Fri, 28 Mar 2008 13:43:34 GMT (515kb)

Title: Dipole Oscillations of a Bose-Einstein Condensate in Presence of Defects
   and Disorder
Authors: M. Albert, T. Paul, N. Pavloff, P. Leboeuf
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We consider dipole oscillations of a trapped dilute Bose-Einstein condensate
in the presence of a scattering potential consisting either in a localized
defect or in an extended disordered potential. In both cases the breaking of
superfluidity and the damping of the oscillations are shown to be related to
the appearance of a nonlinear dissipative flow. At supersonic velocities the
flow becomes asymptotically dissipationless.
\\ ( , 515kb)
Date: Fri, 28 Mar 2008 17:43:00 GMT (36kb)

Title: Universal and nonuniversal contributions to block-block entanglement in
   many-fermion systems
Authors: Vivian V. Franca and Klaus Capelle
Categories: cond-mat.stat-mech cond-mat.str-el
Comments: 6 pages, 3 figures
   We calculate the entanglement entropy of blocks of size x embedded in a
larger system of size L, by means of a combination of analytical and numerical
techniques. The complete entanglement entropy in this case is a sum of three
terms. One is a universal x and L-dependent term, first predicted by Calabrese
and Cardy, the second is a nonuniversal term arising from the thermodynamic
limit, and the third is a finite size correction. We give an explicit
expression for the second, nonuniversal, term for the one-dimensional Hubbard
model, and numerically assess the importance of all three contributions by
comparing to the entropy obtained from fully numerical diagonalization of the
many-body Hamiltonian. We find that finite-size corrections are very small. The
universal Calabrese-Cardy term is equally small for small blocks, but becomes
larger for x>1. In all investigated situations, however, the by far dominating
contribution is the nonuniversal term steming from the thermodynamic limit.
\\ ( , 36kb)
arXiv:0803.1463 (*cross-listing*)
Date: Mon, 10 Mar 2008 19:52:50 GMT (19kb)

Title: Preparation of Entangled States by Dissipative Quantum Markov Processes
Authors: B. Kraus, S. Diehl, A. Micheli, A. Kantian, H. P. B\"uchler, and P.
Categories: quant-ph cond-mat.other
   We investigate the possibility of using a dissipative process to prepare a
quantum system in a desired state. We derive for any multipartite pure state a
dissipative process for which this state is the unique stationary state.
Furthermore we solve the corresponding master equation analytically, which
allows us to compute, for instance, the relaxation time of the dissipative
process. For certain states, like the 2D--Cluster states, it is shown that the
jump operators can be chosen quasi--locally, i.e. they act non--trivially only
on a few, neighboring qubits. We demonstrate the general formalism by
considering arbitrary MPS--PEPS states.
\\ ( , 19kb)
Date: Fri, 28 Mar 2008 09:22:59 GMT (534kb,D)

Title: Engineering the quantum transport of atomic wavefunctions over
   macroscopic distances
Authors: A. Alberti, V. V. Ivanov, G. M. Tino and G. Ferrari
Categories: quant-ph
Comments: 5 pages, 5 figures
   The manipulation of matterwave represents a milestone in the history of
quantum mechanics. It was at the basis of its experimental validation through
the observation of diffraction of matter on crystals, as well as grating and
Young's double-slit interference with electrons, neutron, atoms and molecules.
More recently matterwave manipulation has become a building block in the
implementation of quantum devices such as quantum sensors and it plays an
essential role in many proposals for implementing quantum computers. In this
letter we coherently control the spatial extent of the wavefunction by
reversibly stretching and shrinking the wavefunction over a millimeter
distance. The remarkable experimental simplicity of the scheme would ease
applications in the field of quantum transport and quantum computing.
\\ ( , 534kb)
Date: Fri, 28 Mar 2008 16:27:30 GMT (9kb)

Title: Symplectic tomography of ultracold gases in tight-waveguides
Authors: A. del Campo, V. I. Man'ko, G. Marmo
Categories: quant-ph
Comments: 5 pages, no figures
   The phase space is the natural ground to smoothly extrapolate between local
and non-local correlation functions. With this objective, we introduce the
symplectic tomography of many-body quantum gases in tight-waveguides, and
concentrate on the reduced single-particle symplectic tomogram (RSPST) whose
marginals are the density profile and momentum distribution. We present an
operational approach to measure the RSPST from the time evolution of the
density profile after shutting off the interactions in a variety of relevant
situations: free expansion, fall under gravity, and oscillations in a harmonic
trap. From the RSPST, the one-body density matrix of the trapped state can be
\\ ( , 9kb)
Date: Fri, 28 Mar 2008 19:26:33 GMT (141kb,D)

Title: Atomic Zitterbewegung
Authors: M. Merkl, F. E. Zimmer, G. Juzeliunas, P. \"Ohberg
Categories: quant-ph
Comments: 6 pages, 4 figures
   Ultra-cold atoms which are subject to ultra-relativistic dynamics are
investigated. By using optically induced gauge potentials we show that the
dynamics of the atoms is governed by a Dirac type equation. To illustrate this
we study the trembling motion of the centre of mass for an effective two level
system, historically called Zitterbewegung. Its origin is described in detail,
where in particular the role of the finite width of the atomic wave packets is
seen to induce a damping of both the centre of mass dynamics and the dynamics
of the populations of the two levels.
\\ ( , 141kb)
Date: Fri, 28 Mar 2008 15:48:43 GMT (641kb)

Title: Demonstration of perfect coherence preservation for matter-waves
   perturbed by a delta-kicked rotor
Authors: A. Tonyushkin, S. Wu, and M. Prentiss
Categories: physics.atom-ph
Comments: 5 pages, 5 figures
   We demonstrate perfect coherence preservation in an atom interferometer
perturbed by optical standing wave pulses acting as a kicked rotor. In our
experiment we subject a cloud of cold rubidium atoms in a magnetic guide to
periodic kicks from a sinusoidal potential created by standing wave pulses of
off-resonant laser light propagating along the guiding direction. While, in
general, we observed a strong decoherence of matter-waves due to applied
perturbations the coherence is perfectly preserved for the conditions similar
but not limited to quantum resonances of the quantum kicked rotor. Moreover,
these conditions do not depend on the number of kicks applied or require any
regularity in the pulse strengths. We show that the narrowing of the width of
coherence revival as a function of increasing kick number provides a new method
for precise measurement of recoil frequency.
\\ ( , 641kb)
Date: Fri, 28 Mar 2008 08:11:02 GMT (20kb)

Title: Crime and punishment in scientific research
Authors: Mathieu Bouville
Categories: physics.soc-ph physics.hist-ph
Comments: 10 pages, 2 tables
   Arguments against scientific misconduct one finds in the literature generally
fail to support current policies on research fraud: they may not prove wrong
what is typically considered research misconduct and they tend to make wrong
things that are not usually seen as scientific fraud, in particular honest
errors. I argue that society cannot set a rule enjoining scientists to be
honest, so any such rule can only be internal to science. Therefore society
cannot legitimately enforce it. Moreover, until an argument is provided to
prove that lack of honesty is far worse than lack of technical competence,
intentional deceit should not be punished much more harshly than technical
   Keywords: cheating; ethics; fabrication; falsification; integrity;
plagiarism; research fraud; scientific misconduct.
\\ ( , 20kb)
Date: Fri, 28 Mar 2008 22:36:55 GMT (43kb)

Title: Small mass- and trap-imbalanced two-component Fermi systems
Authors: D. Blume
Categories: cond-mat.other
Comments: 13 pages, 9 figures
   Motivated by the prospect of optical lattice experiments with two-component
Fermi gases consisting of different atomic species such as Li and K, we
calculate the energies for N fermions under harmonic confinement as a function
of the mass- and trap-imbalance, i.e., as a function of the ratio between the
masses and frequencies of species one and two, using microscopic approaches.
Our energies for N=2 through 6 can be used to determine the energetically most
favorable configuration for a given number of atoms per species of a deep
lattice in which each lattice site is approximately harmonic and in which
tunneling between neighboring sites can be neglected. Furthermore, our energies
determine one of the input parameters, namely the onsite interaction strength,
of the corresponding lattice Hamiltonian. We also determine and interpret the
excitation gap for unequal-mass systems with up to N=13 atoms for equal
oscillator lengths.
\\ ( , 43kb)
Date: Sun, 30 Mar 2008 21:01:28 GMT (287kb)

Title: Multiband-Driven Superfluid-Insulator Transition of Fermionic Atoms in
   Optical Lattices: A Dynamical Mean-Field-Theory Study
Authors: Takuji Higashiyama, Kensuke Inaba, and Sei-ichiro Suga
Categories: cond-mat.other cond-mat.supr-con
Comments: 4 pages, 3 figures, to appear in Phys. Rev. A
   The superfluid-insulator transitions of the fermionic atoms in optical
lattices are investigated by the two-site dynamical mean-field theory. It is
shown that the Mott transition occurs as a result of the multiband effects. The
quasiparticle weight in the superfluid state decreases significantly, as the
system approaches the Mott transition point. By changing the interaction and
the orbital splitting, we obtain the phase diagram at half filling. The
numerical results are discussed in comparison with the effective boson model.
\\ ( , 287kb)
Date: Mon, 31 Mar 2008 11:04:52 GMT (157kb)

Title: Three-dimensional correlated-fermion phase separation from analysis of
   the geometric mean of the individual susceptibilities
Authors: Ji-sheng Chen, Fang Qin, and Yan-ping Wang
Categories: cond-mat.stat-mech
Comments: 4 pages, 5 figures
   A quasi-Gaussian approximation scheme is formulated for the strongly
correlated imbalanced fermions thermodynamics, where the mean-field theory is
not applicable. The non-Gaussian correlation effects are understood to be
captured by the statistical geometric mean of the individual susceptibilities.
In the three-dimensional unitary fermions ground state, a {\em universal}
nonlinear scaling transformation relates the physical chemical potentials with
the individual Fermi kinetic energies. For the partial polarization phase
separation to full polarization, the calculated critical polarization ratio is
$P_C={[1-(1-\xi)^{6/5}]}/{[1+(1-\xi)^{6/5}]}\doteq 0.34$. It agrees with the
Monte Carlo calculations and experimental measurements very well.
\\ ( , 157kb)
Date: Mon, 31 Mar 2008 10:05:55 GMT (91kb)

Title: The role of interactions in spin-polarised atomic Fermi gases at
Authors: A. Recati, C. Lobo, S. Stringari
Categories: cond-mat.other
Comments: 6 pages, 2 figures
   We study the zero temperature properties of a trapped polarized Fermi gas at
unitarity by assuming phase separation between an unpolarized superfluid and a
polarized normal phase. The effects of the interaction are accounted using the
formalism of quasi-particles to build up the equation of state of the normal
phase with the Monte Carlo results for the relevant parameters. Our predictions
for the Chandrasekhar-Clogston limit of critical polarization and for the
density profiles, including the density jump at the interface, are confirmed
with excellent accuracy by the recent experimental results at MIT. The role of
interaction on the radial width of the minority component, on the gap of the RF
transition and on the spin oscillations in the normal phase is also discussed.
Our analysis points out the Fermi liquid nature of these strongly interacting
spin polarized configurations.
\\ ( , 91kb)
arXiv:0803.0890 (*cross-listing*)
Date: Thu, 6 Mar 2008 15:29:45 GMT (342kb)
Date (revised v2): Mon, 31 Mar 2008 18:10:38 GMT (342kb)

Title: Locality of dynamics in general harmonic quantum systems
Authors: M. Cramer, A. Serafini, J. Eisert
Categories: quant-ph cond-mat.stat-mech
Comments: 19 pages latex, contribution to proceedings of "Quantum Information
   and Many-Body Quantum Systems" Workshop, 26-31 Mar 2007, Pisa. (v2) minor
   The Lieb-Robinson theorem states that locality is approximately preserved in
the dynamics of quantum lattice systems. Whenever one has finite-dimensional
constituents, observables evolving in time under a local Hamiltonian will
essentially grow linearly in their support, up to exponentially suppressed
corrections. In this work, we formulate Lieb-Robinson bounds for general
harmonic systems on general lattices, for which the constituents are
infinite-dimensional, as systems representing discrete versions of free fields
or the harmonic approximation to the Bose-Hubbard model. We consider both local
interactions as well as infinite-ranged interactions, showing how corrections
to locality are inherited from the locality of the Hamiltonian: Local
interactions result in stronger than exponentially suppressed corrections,
while non-local algebraic interactions result in algebraic suppression. We
derive bounds for canonical operators, Weyl operators and outline
generalization to arbitrary operators. As an example, we discuss the
Klein-Gordon field, and see how the approximate locality in the lattice model
becomes the exact causality in the field limit. We discuss the applicability of
these results to quenched lattice systems far from equilibrium, and the
dynamics of quantum phase transitions.
\\ ( , 342kb)
Date: Sun, 30 Mar 2008 22:06:57 GMT (279kb,D)

Title: Experimental observation of oscillating and interacting matter wave dark
Authors: A. Weller, J.P. Ronzheimer, C. Gross, D.J. Frantzeskakis, G.
   Theocharis, P.G. Kevrekidis, J. Esteve, and M.K. Oberthaler
Categories: quant-ph
Comments: 5 pages, 3 figures
   We report on the generation, subsequent oscillation and interaction of a pair
of matter wave dark solitons. These are created by releasing a Bose-Einstein
condensate from a double well potential into a harmonic trap in the crossover
regime between one dimension (1D) and three dimensions (3D). The oscillation of
the solitons is observed and the frequency is in quantitative agreement with
simulations using the Gross-Pitaevskii equation. An effective particle picture
is developed and reveals that the deviation of the observed frequencies from
the asymptotic prediction $\nu_{z}/\sqrt{2}$, where $\nu_{z}$ is the
longitudinal trapping frequency, results from the dimensionality of the system
and the interaction between the solitons.
\\ ( , 279kb)
Date: Sat, 29 Mar 2008 17:43:59 GMT (517kb)

Title: Gravito--magnetic trapping of $^{87}$Rb
Authors: A. Bertoldi and L. Ricci
Categories: physics.atom-ph
Comments: 3 figures
   Three--dimensional trapping of neutral atoms in a combined gravito--magnetic
potential is reported. Clouds of cold rubidium atoms in different hyperfine
states of the ground level were trapped with a lifetime of 4.5 s. Confinement
exclusively occured as a combination of the static magnetic force and the
gravitational force.
\\ ( , 517kb)
Date: Mon, 31 Mar 2008 17:23:11 GMT (109kb)

Title: Frequency evaluation of the doubly forbidden $^1S_0\to ^3P_0$ transition
   in bosonic $^{174}$Yb
Authors: N. Poli, Z. W. Barber, N. D. Lemke, C. W. Oates, L. S. Ma, J. E.
   Stalnaker, T. M. Fortier, S. A. Diddams, L. Hollberg, J. C. Bergquist, A.
   Brusch, S. Jefferts, T. Heavner, T. Parker
Categories: physics.atom-ph physics.gen-ph
Comments: 4 pages, 3 figure -Submitted to PRA Rapid Communications
   We report an uncertainty evaluation of an optical lattice clock based on the
$^1S_0\leftrightarrow^3P_0$ transition in the bosonic isotope $^{174}$Yb by use
of magnetically induced spectroscopy. The absolute frequency of the
$^1S_0\leftrightarrow^3P_0$ transition has been determined through comparisons
with optical and microwave standards at NIST. The weighted mean of the
evaluations is $\nu$($^{174}$Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty
due to systematic effects has been reduced to less than 0.8 Hz, which
represents $1.5\times10^{-15}$ in fractional frequency.
\\ ( , 109kb)
Date: Mon, 31 Mar 2008 20:00:32 GMT (970kb,D)

Title: Stochastic Mean-Field Theory for the Disordered Bose-Hubbard Model at
Authors: U. Bissbort, W. Hofstetter
Categories: cond-mat.dis-nn cond-mat.other
Comments: 4 pages, 5 figures
   We investigate the effect of diagonal disorder on bosons in an optical
lattice described by an Anderson-Hubbard model at zero temperature. It is known
that within Gutzwiller mean-field theory spatially resolved calculations suffer
particularly from finite system sizes in the disordered case, while arithmetic
averaging of the order parameter cannot describe the Bose glass phase for
finite hopping $J>0$. Here we present and apply a new stochastic mean-field
theory which captures localization due to disorder, includes dimensional
effects and is applicable in the thermodynamic limit. In contrast to fermionic
systems, we find the existence of a critical hopping strength, above which the
system remains superfluid for arbitrarily strong disorder.
\\ ( , 970kb)
Date: Mon, 31 Mar 2008 20:00:54 GMT (453kb)

Title: Emergent complexity: what uphill analysis or downhill invention can not
Authors: Dante R. Chialvo
Categories: cond-mat.dis-nn q-bio.NC
   In these notes we review emergent phenomena in complex systems, emphasizing
ways to identify potential underlying universal mechanisms that generates
complexity. The discussion is centered around the emergence of collective
behavior in dynamical systems when they are poised near a critical point of a
phase transition, either by tuning or by self-organization. We then argue the
rationale for our proposal that the brain is naturally poised near criticality
reviewing recent results as well as the implications of this view of the
functioning brain.
\\ ( , 453kb)
Date: Tue, 1 Apr 2008 00:29:43 GMT (57kb)

Title: Theory of ground state factorization in quantum cooperative systems
Authors: S. M. Giampaolo, G. Adesso, F. Illuminati
Categories: cond-mat.other
Comments: 4 pages, 1 figure
   We introduce a general analytic approach to the study of factorization points
and factorized ground states in quantum cooperative systems. The method allows
to determine rigorously existence, location, and exact form of separable ground
states in a large variety of, generally non-exactly solvable, spin models
belonging to different universality classes. The theory applies to
translationally invariant systems, irrespective of spatial dimensionality, and
for spin-spin interactions of arbitrary range.
\\ ( , 57kb)
Date: Mon, 31 Mar 2008 21:45:23 GMT (201kb)

Title: Towards r-space Bose-Einstein condensation of photonic crystal exciton
Authors: D. L. Boiko
Categories: cond-mat.mes-hall cond-mat.str-el
Comments: 6 pages, 4 figures
   Coupled states of semiconductor quantum well (QW) excitons and photons in a
two dimensional (2D) periodic lattice of microcavities are analyzed
theoretically, revealing allowed bands and forbidden gaps in the energy
spectrum of exciton polaritons. Photonic crystal exciton polaritons have
spatially uniform excitonic constituent set by flat QWs, but exhibit periodic
Bloch oscillations in the plane of QWs due to their photonic component. The
envelope functions of photonic crystal exciton polaritons can be tailored via
effective potential of a photonic crystal heterostructure, by using
quasi-periodic lattices of microcavities. Confined envelope function states of
lower and upper polaritons and the Bose-Einstein condensation of lower
polaritons are analyzed here in a photonic crystal heterostructure trap with
harmonic oscillator potential. This concept is numerically illustrated on
example of CdTe/CdMgTe microcavities.
\\ ( , 201kb)
Date: Tue, 1 Apr 2008 18:16:25 GMT (353kb)

Title: Fast, Runaway Evaporative Cooling to Bose-Einstein Condensation in
   Optical Traps
Authors: Chen-Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin
Categories: cond-mat.other
   We demonstrate a simple scheme to achieve fast, runaway evaporative cooling
of optically trapped atoms by tilting the optical potential with a magnetic
field gradient. Runaway evaporation is possible in this trap geometry due to
the weak dependence of vibration frequencies on trap depth, which preserves
atomic density during the evaporation process. Using this scheme, we show that
Bose-Einstein condensation with ~10^5 cesium atoms can be realized in 2~4 s of
forced evaporation. The evaporation speed and energetics are consistent with
the three-dimensional evaporation picture, despite the fact that atoms can only
leave the trap in the direction of tilt.
\\ ( , 353kb)
Date: Tue, 1 Apr 2008 14:59:00 GMT (1000kb)

Title: Dipolar spinor Bose-Einstein condensates
Authors: Su Yi and Han Pu
Categories: cond-mat.other
Comments: 12 pages, 10 figures. A review on our recent work on dipolar spinor
   BECs, to appear in the book "Electromagnetic, Magnetostatic and Exchange
   Interaction Vortices in Confined Magnetic Structures"
   Under many circumstances, the only important two-body interaction between
atoms in ultracold dilute atomic vapors is the short-ranged isotropic s-wave
collision. Recent studies have shown, however, that situations may arise where
the dipolar interaction between atomic magnetic or electric dipole moments can
play a significant role. The long-range anisotropic nature of the dipolar
interaction greatly enriches the static and dynamic properties of ultracold
atoms. In the case of dipolar spinor condensates, the interplay between the
dipolar interaction and the spin exchange interaction may lead to nontrivial
spin textures. Here we pay particular attention to the spin vortex state that
is analogous to the magnetic vortex found in thin magnetic films.
\\ ( , 1000kb)
Date: Tue, 1 Apr 2008 16:50:52 GMT (868kb)

Title: Mesoscopic Phase Coherence in a Quantum Spin Fluid
Authors: Guangyong Xu, C. Brohol, Yeong-Ah Soh, G. Aeppli, J. F. DiTusa, Ying
   Chen, M. Kenzelmann, C. D. Frost, T. Ito, K. Oka, H. Takagi
Categories: cond-mat.str-el
Journal-ref: Science 317, 1049 (2007)
   Mesoscopic quantum phase coherence is important because it improves the
prospects for handling quantum degrees of freedom in technology. Here we show
that the development of such coherence can be monitored using magnetic neutron
scattering from a one-dimensional spin chain Y2BaNiO5, a quantum spin fluid
where no classical, static magnetic order is present. In the cleanest samples,
the quantum coherence length is 20 nm, almost an order of magnitude larger than
the classical antiferromagnetic correlation length of 3 nm. We also demonstrate
that the coherence length can be modified by static and thermally activated
defects in a quantitatively predictable manner.
\\ ( , 868kb)
Date: Tue, 1 Apr 2008 08:41:52 GMT (212kb)

Title: Multiple Cold-Atom Lasers
Authors: William Guerin (INLN), Franck Michaud (INLN), Robin Kaiser (INLN)
Categories: physics.atom-ph physics.optics
Proxy: ccsd hal-00268718
   We realize a laser with a cloud of cold rubidium atoms as gain medium, placed
in a low-finesse cavity. Three different regimes of laser emission are observed
corresponding respectively to Mollow, Raman and Four Wave Mixing mechanisms. We
measure output power of up to 300 $\mu$W and present threshold and gain spectra
in each regime.
\\ ( , 212kb)
Date: Tue, 1 Apr 2008 20:02:33 GMT (401kb)

Title: Fock-space quantum particle approach for the two-mode boson model
   describing BEC trapped in a double-well potential
Authors: V. S. Shchesnovich and M. Trippenbach
Categories: cond-mat.other
Comments: 14 pages, 13 figures
   We develop the Fock-space many-body quantum approach for large number of
bosons, when the bosons occupy significantly only few modes. The approach is
based on an analogy with the dynamics of a single particle of either positive
or negative mass in a quantum potential, where the inverse number of bosons
plays the role of Planck constant. As application of the method we consider the
Bose-Einstein condensate in a double-well trap. The ground state of positive
mass particle corresponds to the mean-field fixed point of lower energy, while
that of negative mass to the excited fixed point. In the case of attractive BEC
above the threshold for symmetry breaking, the ground state is a cat state and
we relate this fact to the double-well shape of the quantum potential for the
positive mass quantum particle. The tunneling energy splitting between the
local Fock states of the cat state is shown to be extremely small for the
nonlinearity parameter just above the critical value and exponentially
decreasing with the number of atoms. In the repulsive case, the phase locked
($\pi$-phase) macroscopic quantum self-trapping of BEC is related to the
double-well structure of the potential for the negative mass quantum particle.
We also analyze the running phase macroscopic quantum self-trapping state and
show that it is subject to quantum collapses and revivals. Moreover, the
quantum dynamics just before the first collapse of the running phase shows
exponential growth of dispersion of the quantum phase distribution which may
explain the growth of the phase fluctuations seen in the experiment on the
macroscopic quantum self-trapping.
\\ ( , 401kb)
Date: Wed, 2 Apr 2008 04:19:11 GMT (402kb,D)

Title: Quasi-condensation and coherence in the quasi-two-dimensional trapped
   Bose gas
Authors: R.N. Bisset, M.J. Davis, T.P. Simula, and P.B. Blakie
Categories: cond-mat.other
Comments: 4.1 pages, 4 figures
   We simulate a trapped quasi-two-dimensional Bose gas using a classical field
method. To interpret our results we introduce two characteristic temperatures
determined from our simulations: the condensation temperature $T_{c}$ and the
uniform Berezinskii-Kosterlitz-Thouless (BKT) temperature $T_{BKT}$. We observe
that density fluctuations are suppressed in the system above $T_c$ as a
quasi-condensate forms as the first manifestation of degeneracy. At $T_c$ a
coherent condensate forms, which has a clear bimodal structure in momentum
space. At $T_{BKT}$ algebraic decay of off-diagonal correlations occurs near
the trap center when the peak density satisfies the uniform condition for the
BKT phase transition. Our results provide a comprehensive picture of the low
temperature phase diagram of the trapped quasi-2D Bose gas and a consistent
interpretation of recent experiments.
\\ ( , 402kb)
Date: Wed, 2 Apr 2008 13:58:29 GMT (19kb)

Title: Pair-Breaking in Rotating Fermi Gases
Authors: Michael Urban and Peter Schuck
Categories: cond-mat.other
Comments: 4 pages, 2 figures
   We study the pair-breaking effect of rotation on a cold Fermi gas in the
BCS-BEC crossover region. In the framework of BCS theory, which is supposed to
be qualitatively correct at zero temperature, we find that in a trap rotating
around a symmetry axis, three regions have to be distinguished: (A) a region
near the rotational axis where the superfluid stays at rest and where no pairs
are broken, (B) a region where the pairs are progressively broken with
increasing distance from the rotational axis, resulting in an increasing
rotational current, and (C) a normal-fluid region where all pairs are broken
and which rotates like a rigid body. Due to region B, density and current do
not exhibit any discontinuities.
\\ ( , 19kb)
Date: Wed, 2 Apr 2008 14:35:33 GMT (108kb)

Title: Second order quantum phase transition of a homogeneous Bose gas with
   attractive interactions
Authors: P. Zi\'n, B. Ole\'s, M. Trippenbach, and K. Sacha
Categories: cond-mat.other
Comments: 7 pages, 3 figures
   We consider a homogeneous Bose gas of particles with an attractive
interaction. Mean field theory predicts for this system a spontaneous symmetry
breaking at a certain value of the interaction strength. We show that at this
point a second-order quantum phase transition occurs. We investigate the system
in the vicinity of the critical point using Bogoliubov theory and a continuous
description, that allows us to analyze {\it quantum fluctuations} in the system
even when the Bogoliubov approach breaks down.
\\ ( , 108kb)
Date: Wed, 2 Apr 2008 00:16:03 GMT (412kb,D)

Title: Quantum computing using shortcuts through higher dimensions
Authors: B. P. Lanyon, M. Barbieri, M. P. Almeida, T. Jennewein, T. C. Ralph,
   K. J. Resch, G. J. Pryde, J. L. O'Brien, A. Gilchrist and A. G. White
Categories: quant-ph
Comments: 7 pages, 6 figures
   Quantum computation offers the potential to solve fundamental yet otherwise
intractable problems across a range of active fields of research. Recently,
universal quantum-logic gate sets - the building blocks for a quantum computer
- have been demonstrated in several physical architectures. A serious obstacle
to a full-scale implementation is the sheer number of these gates required to
implement even small quantum algorithms. Here we present and demonstrate a
general technique that harnesses higher dimensions of quantum systems to
significantly reduce this number, allowing the construction of key quantum
circuits with existing technology. We are thereby able to present the first
implementation of two key quantum circuits: the three-qubit Toffoli and the
two-qubit controlled-unitary. The gates are realised in a linear optical
architecture, which would otherwise be absolutely infeasible with current
\\ ( , 412kb)
Date: Wed, 2 Apr 2008 14:52:36 GMT (83kb)

Title: Quasi-analytical theory for the anomalous quantum reflection of
   Bose-Einstein condensates
Authors: Alexander Jurisch and Jan-Michael Rost
Categories: quant-ph
Comments: 4 pages, 1 figure
   We develop a quasi-analytical theory for the anomalous quantum reflection
amplitude of Bose-Einstein condensates in the asymptotic time-domain. We derive
and calculate the decay-width of a Bose-Einstein condensate. A general relation
between the time-dependent decay-law of the system and its quantum reflection
amplitude allows us to explain the quantum reflection anomaly of Bose-Einstein
condensates present in BEC-surface systems as a direct consequence of the
mean-field particle-interaction.
\\ ( , 83kb)
Date: Wed, 2 Apr 2008 04:40:04 GMT (8kb)

Title: Concept of momentum-less bodies and a suggestion for its experimental
   verification using ultra-cold atoms
Authors: Sanjay M. Wagh
Categories: physics.gen-ph
Comments: 4 pages, No figures
   General Principle of Relativity unequivocally supports the notion of
momentum-less energy for bodies (energy-quanta) moving at the {\em same} or
{\em constant} speed relative to all the reference systems. In this
communication, we point out that whether energy-quantum is a momentum-less body
or not is verifiable using ultra-cold atoms trapped in an optical lattice,
perhaps with some minor modifications to the existing such experimental setups.
\\ ( , 8kb)
Date: Thu, 3 Apr 2008 08:18:43 GMT (670kb)

Title: Stability of superfluid and supersolid phases of dipolar bosons in
   optical lattices
Authors: Ippei Danshita, Carlos A. R. S\'a de Melo
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We perform a stability analysis of superfluid and supersolid phases of
polarized dipolar bosons in two-dimensional optical lattices at zero
temperature, and obtain the phase boundaries between superfluid (SF),
checkerboard supersolid (CS), striped supersolid (SS), and collapse (CO). We
show that the phase diagram can be explored through the application of an
external field and the tuning of its direction with respect to the optical
lattice plane. In particular, we find a discontinuous (first-order) transition
between the CS and SS phases, characterized by hysteretic behavior. Finally, we
discuss measurable quantities such as the excitation spectrum and the momentum
distribution as a way of identifying all possible phases.
\\ ( , 670kb)
Date: Thu, 3 Apr 2008 11:51:29 GMT (471kb)

Title: In situ Ramsey Interferometry and Diffraction Echo with an Ultracold
   Fermi Gas
Authors: C. Marzok, B. Deh, S. Slama, C. Zimmermann, and Ph.W. Courteille
Categories: cond-mat.other
Comments: 5 pages, 4 figures
   We report on the first observation of Bragg scattering of an ultracold $^6$Li
Fermi gas. We demonstrate a Ramsey-type matter-wave interferometer based on
Bragg diffraction and find robust signatures of persistent matter wave
coherences using an echo pulse sequence. Because of the Pauli principle, the
diffracted fermions oscillate nearly unperturbed in the trapping potential for
long times beyond 2 s. This suggests extremely long coherence times. On these
timescales, only the presence of a $^{87}$Rb cloud seems sufficient to induce
noticeable perturbations.
\\ ( , 471kb)
Date: Thu, 3 Apr 2008 14:24:21 GMT (736kb,D)

Title: Oscillations and interactions of dark and dark-bright solitons in
   Bose-Einstein condensates
Authors: C. Becker, S. Stellmer, P. Soltan-Panahi, S. D\"orscher, M. Baumert,
   E.-M. Richter, J. Kronj\"ager, K. Bongs and K. Sengstock
Categories: cond-mat.other
Comments: 9 pages, 4 figures
   Solitons are among the most distinguishing fundamental excitations in a wide
range of non-linear systems such as water in narrow channels, high speed
optical communication, molecular biology and astrophysics. Stabilized by a
balance between spreading and focusing, solitons are wavepackets, which share
some exceptional generic features like form-stability and particle-like
properties. Ultra-cold quantum gases represent very pure and well-controlled
non-linear systems, therefore offering unique possibilities to study soliton
dynamics. Here we report on the first observation of long-lived dark and
dark-bright solitons with lifetimes of up to several seconds as well as their
dynamics in highly stable optically trapped $^{87}$Rb Bose-Einstein
condensates. In particular, our detailed studies of dark and dark-bright
soliton oscillations reveal the particle-like nature of these collective
excitations for the first time. In addition, we discuss the collision between
these two types of solitary excitations in Bose-Einstein condensates.
\\ ( , 736kb)
Date: Thu, 3 Apr 2008 05:19:45 GMT (629kb)

Title: Atomic noise spectra in nonlinear magneto-optical rotation in a rubidium
Authors: Hebin Li, Vladimir A. Sautenkov, Tigran S. Varzhapetyan, Yuri V.
   Rostovtsev, and Marlan O. Scully
Categories: quant-ph
Comments: 5 pages, 5 figures
   We have studied the noise spectra in a nonlinear magneto-optical rotation
experiment in a rubidium vapor. We observed the reduction of noise in the
intensity difference of two orthogonally polarized components of the laser
beam. The dependence of the noise level on both the frequency and the
longitudinal magnetic field has been studied. We found that the optimal
condition for the noise reduction is to work around zero longitudinal magnetic
field, where the intensity correlation between the two orthogonally polarized
components is maximum. Our results can be used to reduce or eliminate the
atomic excess noise, therefore improving the sensitivity of nonlinear
magneto-optical rotation magnetometers and other atom-optical based
\\ ( , 629kb)

The replacements:

replaced with revised version Fri, 28 Mar 2008 16:16:50 GMT (492kb)

Title: Mott transition of fermionic atoms in a three-dimensional optical trap
Authors: R. W. Helmes, T. A. Costi and A. Rosch
Categories: cond-mat.str-el cond-mat.other
Comments: 4 pages and 5 figures
Journal-ref: PRL 100, 056403 (2008)
\\ ( , 492kb)
replaced with revised version Fri, 28 Mar 2008 14:11:24 GMT (253kb,D)

Title: Determination of the Equation of State of a Two-Component Fermi Gas at
Authors: Yong-il Shin
Categories: cond-mat.stat-mech
Comments: 4 pages, 3 figures / typo correction / figure replacement
\\ ( , 253kb)
replaced with revised version Fri, 28 Mar 2008 17:29:07 GMT (126kb)

Title: Anderson localization of a Bose-Einstein condensate in a 3D random
Authors: S.E. Skipetrov, A. Minguzzi, B.A. van Tiggelen, B. Shapiro
Categories: cond-mat.dis-nn cond-mat.mes-hall
Comments: 4 pages, 2 figures
\\ ( , 126kb)
replaced with revised version Sat, 29 Mar 2008 08:45:01 GMT (107kb)

Title: Superfluid Insulator Transitions of Hard-Core Bosons on the Checkerboard
Authors: Arnab Sen, Kedar Damle and T. Senthil
Categories: cond-mat.str-el
Comments: published version
Journal-ref: Phys. Rev. B 76, 235107 (2007)
\\ ( , 107kb)
replaced with revised version Sat, 29 Mar 2008 09:26:31 GMT (34kb)

Title: Unusual liquid state of hard-core bosons on the pyrochlore lattice
Authors: Argha Banerjee, Sergei V. Isakov, Kedar Damle, Yong Baek Kim
Categories: cond-mat.str-el
Comments: published version
Journal-ref: Phys. Rev. Lett. 100, 047208 (2008)
\\ ( , 34kb)
replaced with revised version Mon, 31 Mar 2008 10:04:37 GMT (114kb)

Title: Quantum Phases of Ultracold Bosonic Atoms in a Two-Dimensional Optical
Authors: Jing-Min Hou
Categories: cond-mat.other
\\ ( , 114kb)
arXiv:0705.3456 (*cross-listing*)
replaced with revised version Mon, 31 Mar 2008 18:39:05 GMT (671kb)

Title: Unifying variational methods for simulating quantum many-body systems
Authors: Christopher M. Dawson, Jens Eisert, Tobias J. Osborne
Categories: quant-ph cond-mat.str-el
Comments: 5 pages, 3 figures, replaced with published version
Journal-ref: Phys. Rev. Lett. 100, 130501 (2008)
\\ ( , 671kb)
replaced with revised version Mon, 31 Mar 2008 02:56:56 GMT (39kb)

Title: Canonical Trajectories and Critical Coupling of the Bose-Hubbard
   Hamiltonian in a Harmonic Trap
Authors: G.G. Batrouni, H. R. Krishnamurthy, K. W. Mahmud, V.G. Rousseau, R.T.
Categories: cond-mat.other cond-mat.stat-mech
Comments: New version of figure 1b
\\ ( , 39kb)
arXiv:cond-mat/0610198 (*cross-listing*)
replaced with revised version Mon, 31 Mar 2008 10:56:48 GMT (193kb)

Title: Quantum liquid of repulsively bound pairs of particles in a lattice
Authors: David Petrosyan, Bernd Schmidt, James R. Anglin, Michael Fleischhauer
Categories: cond-mat.other quant-ph
Comments: Corrected dimer energy & references
Journal-ref: Phys. Rev. A 76, 033606 (2007)
DOI: 10.1103/PhysRevA.76.033606
\\ ( , 193kb)
replaced with revised version Tue, 1 Apr 2008 08:31:39 GMT (178kb)

Title: Three fully polarized fermions close to a p-wave Feshbach resonance
Authors: Mattia Jona-Lasinio (LKB - Lhomond, LENS), Ludovic Pricoupenko
   (LPTMC), Yvan Castin (LKB - Lhomond)
Categories: cond-mat.other
Comments: 31 pages, 12 figures
Proxy: ccsd hal-00166351
\\ ( , 178kb)
replaced with revised version Tue, 1 Apr 2008 13:25:57 GMT (30kb)

Title: The effects of next to nearest neighbor hopping on Bose-Einstein
   condensation in cubic lattices
Authors: G. K. Chaudhary and R. Ramakumar
Categories: cond-mat.stat-mech cond-mat.other
Comments: 4 pages including 6 figures, typos corrected
\\ ( , 30kb)
replaced with revised version Tue, 1 Apr 2008 09:04:37 GMT (229kb)

Title: Density modulations in an elongated Bose-Einstein condensate released
   from a disordered potential
Authors: David Cl\'ement (LCFIO), Philippe Bouyer (LCFIO), Alain Aspect
   (LCFIO), Laurent Sanchez-Palencia (LCFIO)
Categories: cond-mat.other quant-ph
Comments: Published version; 4+ pages; 4 figures
Proxy: ccsd hal-00178074
Journal-ref: Physical Review A: Atomic, Molecular and Optical Physics 77 (2008)
\\ ( , 229kb)
replaced with revised version Wed, 2 Apr 2008 19:57:29 GMT (197kb)

Title: Vortex lattice stability and phase coherence in three-dimensional
   rapidly rotating Bose condensates
Authors: S. Andrew Gifford, Gordon Baym
Categories: cond-mat.soft cond-mat.stat-mech
Comments: 10 pages, 2 figures
Journal-ref: Phys. Rev. A 70, 033602 (2004)
\\ ( , 197kb)
replaced with revised version Wed, 2 Apr 2008 02:24:21 GMT (213kb)

Title: Exact Floquet states of a driven condensate and their stabilities
Authors: Wenhua Hai, Chaohong Lee, Qianquan Zhu
Categories: quant-ph
Comments: 14 pages, 3 eps figures, final version accepted for publication in J.
Phys. B
\\ ( , 213kb)

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
Legal stuff: Unless stated otherwise, this e-mail represents only the
views of the sender and not the views of the University of Queensland
Received on Thu Apr 10 2008 - 09:27:39 EST

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