[Matts-arxiv] Matt; s arXiv selection: week ending 11 September 2009

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Fri, 23 Oct 2009 09:34:57 +1000

Dear subscribers,

This week's email was collated by Chao Feng. There are 38 new abstracts and 11

Date: Wed, 15 Jul 2009 17:49:04 GMT (18kb)

Title: Time Irreversibility Problem and Functional Formulation of Classical
Authors: Igor V. Volovich
Categories: cond-mat.stat-mech math-ph math.MP physics.class-ph
Comments: 21 pages
   The time irreversibility problem is the dichotomy of the reversible
microscopic dynamics and the irreversible macroscopic physics. This problem was
considered by Boltzmann, Poincar\'e, Bogolyubov and many other authors and
though some researchers claim that the problem is solved, it deserves a further
study. In this paper an attempt is performed of the following solution of the
irreversibility problem: a formulation of microscopic dynamics is suggested
which is irreversible in time.
   A widely used notion of microscopic state of the system at a given moment of
time as a point in the phase space and also a notion of trajectory does not
have an immediate physical meaning since arbitrary real numbers are non
observable. In the approach presented in this paper the physical meaning is
attributed not to an individual trajectory but only to a bunch of trajectories
or to the distribution function on the phase space.
   The fundamental equation of the microscopic dynamics in the proposed
"functional" approach is not the Newton equation but the Liouville equation for
the distribution function of a single particle. Solutions of the Liouville
equation have the property of delocalization which accounts for
irreversibility. It is shown that the Newton equation in this approach appears
as an approximate equation describing the dynamics of the average values of the
position and momenta. Corrections to the Newton equation are computed.
\\ ( http://arxiv.org/abs/0907.2445 , 18kb)
Date: Wed, 2 Sep 2009 19:18:46 GMT (2783kb)

Title: Light scattering for thermometry of fermionic atoms in an optical
Authors: J. Ruostekoski, C. J. Foot, and A. B. Deb
Categories: cond-mat.quant-gas quant-ph
Comments: submitted to PRL in January 2009
   We propose a method for measuring the temperature of fermionic atoms in an
optical lattice potential from the intensity of the scattered light in the
far-field diffraction pattern. We consider a single-component gas in a
tightly-confined two-dimensional lattice, illuminated by far off-resonant light
driving a cycling transition. Our calculations show that thermal correlations
of the fermionic atoms generate fluctuations in the intensity of the
diffraction pattern of light scattered from the atomic lattice array and that
this signal can be accurately detected above the shot noise using a lens to
collect photons scattered in a forward direction (with the diffraction maxima
blocked). The sensitivity of the thermometer is enhanced by an additional
harmonic trapping potential.
\\ ( http://arxiv.org/abs/0909.0491 , 2783kb)
Date: Thu, 3 Sep 2009 16:27:14 GMT (18kb)

Title: Rabi Interferometry and Sensitive Measurement of the Casimir-Polder
   Force with Ultra-Cold Gases
Authors: Jan Chwede\'nczuk, Luca Pezz\'e, Francesco Piazza and Augusto Smerzi
Categories: quant-ph cond-mat.other
   We show that Rabi oscillations of a degenerate fermionic or bosonic gas
trapped in a double-well potential can be exploited for the interferometric
measurement of external forces at micrometer length scales. The Rabi
interferometer is less sensitive, but easier to implement, than the
Mach-Zehnder since it does not require dynamical beam-splitting/recombination
processes. As an application we propose a measurement of the Casimir-Polder
force acting between the atoms and a dielectric surface. We find that even if
the interferometer is fed with a coherent state of relatively small number of
atoms, and in the presence of realistic experimental noise, the force can be
measured with a sensitivity sufficient to discriminate between thermal and
zero-temperature regimes of the Casimir-Polder potential. Higher sensitivities
can be reached with spin squeezed states.
\\ ( http://arxiv.org/abs/0909.0705 , 18kb)
Date: Thu, 3 Sep 2009 19:56:49 GMT (213kb,D)

Title: Simulating and detecting artificial magnetic fields in trapped atoms
Authors: Matthias Rosenkranz, Alexander Klein, Dieter Jaksch
Categories: cond-mat.quant-gas cond-mat.other quant-ph
Comments: 14 pages, 9 figures
   A Bose-Einstein condensate exhibiting a nontrivial phase induces an
artificial magnetic field in immersed impurity atoms trapped in a stationary,
ring-shaped optical lattice. We present an effective Hamiltonian for the
impurities for two condensate setups: the condensate in a rotating ring and in
an excited rotational state in a stationary ring. We use Bogoliubov theory to
derive analytical formulas for the induced artificial magnetic field and the
hopping amplitude in the limit of low condensate temperature where the impurity
dynamics is coherent. As methods for observing the artificial magnetic field we
discuss time of flight imaging and mass current measurements. Moreover, we
compare the analytical results of the effective model to numerical results of a
corresponding two-species Bose-Hubbard model. We also study numerically the
clustering properties of the impurities and the quantum chaotic behavior of the
two-species Bose-Hubbard model.
\\ ( http://arxiv.org/abs/0909.0728 , 213kb)
Date: Thu, 3 Sep 2009 20:58:01 GMT (109kb)

Title: Soliton creation during a Bose-Einstein condensation
Authors: Bogdan Damski and Wojciech H. Zurek
Categories: cond-mat.quant-gas
Comments: 4+ pages, 3 figures
Report-no: LA-UR 09-05090
   We study the process of soliton creation during a non-equilibrium second
order phase transition. We investigate a simple model (stochastic
Gross-Pitaevskii equation) that simulates many aspects of the normal gas --
Bose-Einstein condensate transition. We show that the quench leads to creation
of solitons, whose density follows a Kibble-Zurek-like scaling law involving
critical exponents.
\\ ( http://arxiv.org/abs/0909.0761 , 109kb)
Date: Fri, 4 Sep 2009 22:52:25 GMT (1578kb,D)

Title: Magnetic structure of an imbalanced Fermi gas in an optical lattice
Authors: B. Wunsch, L. Fritz, N.T. Zinner, E. Manousakis, E. Demler
Categories: cond-mat.quant-gas cond-mat.str-el
Comments: 11 pages, 10 figures
   We analyze the repulsive fermionic Hubbard model on square and cubic lattices
with spin imbalance and in the presence of a parabolic confinement. We analyze
the magnetic structure as a function of the repulsive interaction strength and
polarization. In the first part of the paper we perform unrestricted
Hartree-Fock calculations for the 2D case and find that above a critical
interaction strength $U_c$ the system turns ferromagnetic at the edge of the
trap, in agreement with the ferromagnetic Stoner instability of a homogeneous
system away from half-filling. For $U<U_c$ we find a canted antiferromagnetic
structure in the Mott region in the center and a partially polarized
compressible edge. The antiferromagnetic order in the Mott plateau is
perpendicular to the direction of the imbalance. In this regime the same
qualitative behavior is expected for 2D and 3D systems. In the second part of
the paper we give a general discussion of magnetic structures above $U_c$. We
argue that spin conservation leads to nontrivial textures, both in the
ferromagnetic polarization at the edge and for the Neel order in the Mott
plateau. We discuss differences in magnetic structures for 2D and 3D cases.
\\ ( http://arxiv.org/abs/0909.0976 , 1578kb)
Date: Fri, 4 Sep 2009 08:54:17 GMT (427kb)

Title: Evidence of antiblockade in an ultracold Rydberg gas
Authors: Thomas Amthor, Christian Giese, Christoph S. Hofmann, Matthias
Categories: physics.atom-ph
   We present the experimental observation of the antiblockade in an ultracold
Rydberg gas recently proposed by Ates et al. [Phys. Rev. Lett. 98, 023002
(2007)]. Our approach allows the control of the pair distribution in the gas
and is based on a strong coupling of one transition in an atomic three-level
system, while introducing specific detunings of the other transition. When the
coupling energy matches the interaction energy of the Rydberg long-range
interactions, the otherwise blocked excitation of close pairs becomes possible.
A time-resolved spectroscopic measurement of the Penning ionization signal is
used to identify slight variations in the Rydberg pair distribution of a random
arrangement of atoms. A model based on a pair interaction Hamiltonian is
presented which well reproduces our experimental observations and allows one to
analyze the distribution of nearest neighbor distances.
\\ ( http://arxiv.org/abs/0909.0837 , 427kb)
Date: Fri, 4 Sep 2009 19:01:04 GMT (47kb)

Title: Stability of Bose-Einstein condensates in a circular array
Authors: E. T. D. Matsushita and E. J. V. de Passos
Categories: cond-mat.quant-gas
Comments: 11 pages,2 figures, 5 tables
   The properties of the superfluid phase of ultra cold bosonic atoms loaded in
a circular array are investigated in the framework of the Bose-Hubbard model
and the Bogoliubov theory. We derive and solve the Gross-Pitaevskii equation of
the model to find that the atoms condense in states of well-defined
quasimomentum. A detailed analysis of the coupling structure in the effective
quadratic grand-canonical Hamiltonian shows that only pairs of distinct and
identical quasimomenta are coupled. Solving the corresponding Bogoliubov-de
Gennes equations we see that each pair of distinct quasimomenta gives raise to
doublets in the excitation energy spectrum and that the quasimomenta of the
zero-energy mode and of the occupied state in the condensates are identical.
The dynamical and energetic stabilities of the condensates are determined by
studying the behavior of the elementary excitations in the control parameters
space. Our investigation establishes that superflow condensates exists only in
the central region of the first Brillouin zone whereas there is none in the
last quarters since they are energetically unstable, independently of the
control parameters.
\\ ( http://arxiv.org/abs/0909.0920 , 47kb)
Date: Fri, 4 Sep 2009 13:19:35 GMT (205kb,D)

Title: Second sound dipole mode in a partially Bose-Einstein condensed gas
Authors: R. Meppelink, S. B. Koller, J. M. Vogels, H. T. C. Stoof, and P. van
   der Straten
Categories: cond-mat.quant-gas
Comments: Submitted to Phys. Rev. Lett. with 5 figures
   We study the second sound dipole mode in a partially Bose-Einstein condensed
gas. This mode is excited by spatially separating and releasing the
center-of-mass of the Bose-Einstein condensate (BEC) with respect to the
thermal cloud, after which the equilibration is observed. The oscillation
frequency and the damping rate of this mode is studied for different harmonic
confinements and temperatures. The measured damping rates close to the
collisionless regime are found to be in good agreement with Landau damping. For
increasing hydrodynamicity of the cloud we observe an increase of the damping.
\\ ( http://arxiv.org/abs/0909.0886 , 205kb)
Date: Fri, 4 Sep 2009 08:18:53 GMT (187kb)

Title: Weak coupling regime of the Landau-Zener transition for association of
   an atomic Bose-Einstein condensate
Authors: N. Sahakyan, H. Azizbekyan, H. Ishkhanyan, R. Sokhoyan, and A.
Categories: cond-mat.quant-gas
Comments: accepted for publication in Laser Physics (13 pages, 3 figures)
   In the framework of a basic semiclassical time-dependent nonlinear two-state
problem, we study the weak coupling limit of the nonlinear Landau-Zener
transition at coherent photo- and magneto-association of an atomic
Bose-Einstein condensate. Using an exact third-order nonlinear differential
equation for the molecular state probability, we develop a variational approach
which enables us to construct an accurate analytic approximation describing
time dynamics of the coupled atom-molecular system for the case of weak
coupling. The approximation is written in terms of the solution to an auxiliary
linear Landau-Zener problem with some effective Landau-Zener parameter. The
dependence of this effective parameter on the input Landau-Zener parameter is
found to be unexpected: as the generic Landau-Zener parameter increases, the
effective Landau-Zener parameter first monotonically increases (starting from
zero), reaches its maximal value and then monotonically decreases again
reaching zero at some point. The constructed approximation quantitatively well
describes many characteristics of the time dynamics of the system, in
particular, it provides a highly accurate formula for the final transition
probability to the molecular state. The present result for the final transition
probability improves the accuracy of the previous approximation by Ishkhanyan
et al. [Phys. Rev. A 69, 043612 (2004); J. Phys. A 38, 3505 (2005)] by order of
\\ ( http://arxiv.org/abs/0909.0834 , 187kb)
Date: Fri, 4 Sep 2009 09:47:46 GMT (113kb)

Title: Dynamics for partially coherent Bose-Einstein condensates in double
Authors: Li-Hua Lu and You-Quan Li
Categories: cond-mat.quant-gas
Comments: Revtex, 6 pages, 5 figures, to appear in PRA
   The dynamical properties of partially coherent Bose-Einstein condensates in
double wells are investigated in three typical regimes. In the extreme Fock
regime, the time evolution of the degree of coherence is shown to decay
rapidly. In the Rabi regime, a relation between the amplitude of Rabi
oscillation and the degree of coherence is obtained, which is expected to
determine the degree of coherence by measuring the amplitude of Rabi
oscillation. The study on the self-trapping phenomena in the Josephson regime
exhibits that both the degree of coherence and the initial relative phase can
affect the final particle distribution.
\\ ( http://arxiv.org/abs/0909.0845 , 113kb)
Date: Mon, 7 Sep 2009 09:52:03 GMT (67kb,D)

Title: Interaction regimes in quasi-one-dimensional dipolar Bose gases
Authors: Frank Deuretzbacher, Jonas Christensson, Stephanie M. Reimann
Categories: cond-mat.quant-gas cond-mat.other
   We study a quasi-one-dimensional system of bosons with dipole-dipole
repulsion by means of the exact diagonalization method. Up to three interaction
regimes are found depending on the strength of the interaction potential and
the anisotropy of the trap: A regime, where the dipolar Bose gas resembles a
system of weakly delta-interacting bosons, a second regime, where the bosons
are fermionized, and a third regime, where the bosons form a Wigner crystal. In
the first two regimes the dipole-dipole potential can be replaced by a
delta-potential. In the crystalline state the overlap between the localized
wave packets is strongly reduced and all the properties of the boson system
equal those of its fermionic counterpart.
\\ ( http://arxiv.org/abs/0909.1192 , 67kb)
Date: Mon, 7 Sep 2009 07:53:43 GMT (9kb)

Title: Dynamics of wave packets for the nonlinear Schroedinger equation with a
   random potential
Authors: A. Iomin
Categories: cond-mat.stat-mech cond-mat.dis-nn
Journal-ref: PHYSICAL REVIEW E 80, 037601 (2009)
   The dynamics of an initially localized Anderson mode is studied in the
framework of the nonlinear Schroedinger equation in the presence of disorder.
It is shown that the dynamics can be described in the framework of the
Liouville operator. An analytical expression for a wave function of the initial
time dynamics is found by a perturbation approach. As follows from a
perturbative solution the initially localized wave function remains localized.
At asymptotically large times the dynamics can be described qualitatively in
the framework of a phenomenological probabilistic approach by means of a
probability distribution function. It is shown that the probability
distribution function may be governed by the fractional Fokker-Planck equation
and corresponds to subdiffusion.
\\ ( http://arxiv.org/abs/0909.1158 , 9kb)
Date: Mon, 7 Sep 2009 09:32:00 GMT (40kb)

Title: Scheme of thinking quantum systems
Authors: V.I. Yukalov and D. Sornette
Categories: quant-ph
Comments: Latex file, 15 pages, 1 figure
Journal-ref: Laser Phys. Lett. 6 (2009) 833-839
   A general approach describing quantum decision procedures is developed. The
approach can be applied to quantum information processing, quantum computing,
creation of artificial quantum intelligence, as well as to analyzing decision
processes of human decision makers. Our basic point is to consider an active
quantum system possessing its own strategic state. Processing information by
such a system is analogous to the cognitive processes associated to decision
making by humans. The algebra of probability operators, associated with the
possible options available to the decision maker, plays the role of the algebra
of observables in quantum theory of measurements. A scheme is advanced for a
practical realization of decision procedures by thinking quantum systems. Such
thinking quantum systems can be realized by using spin lattices, systems of
magnetic molecules, cold atoms trapped in optical lattices, ensembles of
quantum dots, or multilevel atomic systems interacting with electromagnetic
\\ ( http://arxiv.org/abs/0909.1186 , 40kb)
Date: Mon, 7 Sep 2009 18:32:50 GMT (112kb)

Title: Finite-density corrections to the Unitary Fermi gas: A lattice
   perspective from Dynamical Mean-Field Theory
Authors: A. Privitera, M. Capone, C. Castellani
Categories: cond-mat.quant-gas cond-mat.supr-con
Comments: 9 pages, 8 figures
   We investigate the approach to the universal regime of the dilute unitary
Fermi gas as the density is reduced to zero in a lattice model. To this end we
study the chemical potential, superfluid order parameter and internal energy of
the attractive Hubbard model in three different lattices with densities of
states (DOS) which share the same low-energy behavior of fermions in
three-dimensional free space: a cubic lattice, a "Bethe lattice" with a
semicircular DOS, and a "lattice gas" with parabolic dispersion and a sharp
energy cut-off that ensures the normalization of the DOS. The model is solved
using Dynamical Mean-Field Theory, that treats directly the thermodynamic limit
and arbitrarily low densities, eliminating finite-size effects. At densities of
the order of one fermion per site the lattice and its specific form dominate
the results. The evolution to the low-density limit is smooth and it does not
allow to define an unambiguous low-density regime. Such finite-density effects
are significantly reduced using the lattice gas, and they are maximal for the
three-dimensional cubic lattice. Even though dynamical mean-field theory is
bound to reduce to the more standard static mean field in the limit of zero
density due to the local nature of the self-energy and of the vertex functions,
it compares well with accurate Monte Carlo simulations down to the lowest
densities accessible to the latter.
\\ ( http://arxiv.org/abs/0909.1298 , 112kb)
Date: Mon, 7 Sep 2009 15:53:09 GMT (502kb)

Title: Near-resonance Light Scattering from a High-density, Ultracold Atomic
   $^{87}$Rb Gas
Authors: S. Balik, A.L. Win and M.D. Havey
Categories: quant-ph
Comments: 10 pages, 11 figures
   We report experimental investigation of hyperfine optical pumping and near
resonance light scattering from a high-density and ultracold atomic $^{87}$Rb
gas. The atomic sample, having a peak density $\sim 5\cdot10^{13}$
atoms/cm$^{3}$, temperature $\sim$ 65 $\mu$K and initially prepared in the F =
1 lower energy $^{87}$Rb hyperfine component, is optically pumped to the higher
energy F = 2 hyperfine level. Measurements are made of the transient hyperfine
pumping process and of the time evolution of scattering of near resonance probe
radiation on the $F = 2 \to F' = 3$ transition. Features of the density,
detuning, and probe laser intensity dependence of the signals are attributed to
the high peak density and consequent large optical depth of the samples.
\\ ( http://arxiv.org/abs/0909.1133 , 502kb)
Date: Mon, 7 Sep 2009 20:37:20 GMT (31kb)

Title: Expectation Values in the Lieb-Liniger Bose Gas
Authors: M. Kormos, G. Mussardo, A. Trombettoni
Categories: cond-mat.stat-mech cond-mat.quant-gas
   The expectation values of field operators are basic quantities of any
interacting quantum theory, both for theoretical and experimental reasons. We
present a novel method to compute, at zero and finite temperature, expectation
values in the Lieb-Liniger model. These quantities, relevant in the physics of
one-dimensional ultracold Bose gases, are expressed by a series that has a
remarkable behaviour of convergence. Among other results, we show the
computation of the three-body expectation value at finite temperature, a
quantity that rules the recombination rate of the Bose gas.
\\ ( http://arxiv.org/abs/0909.1336 , 31kb)
Date: Mon, 7 Sep 2009 17:23:24 GMT (1074kb)

Title: Exact Solution of Bogoliubov Equations for Bosons in One-Dimensional
   Piecewise Constant Potential
Authors: Daisuke Takahashi
Categories: cond-mat.quant-gas
Comments: 12 pages, 15 figures
   We show that Bogoliubov equations in one-dimensional systems with piecewise
constant potentials can be always solved. In particular, we analyze in detail
the case where the condensate wavefunction is a real-valued function, and give
the explicit expressions for wavefunctions of Bogoliubov excitations. By means
of these solutions, we consider transmission and reflection properties of
Bogoliubov excitations for two types of potential, namely, a rectangular
barrier and a potential step. The results yield simple and exact examples of
anomalous tunneling effect and quantum evaporation.
\\ ( http://arxiv.org/abs/0909.1068 , 1074kb)
Date: Mon, 7 Sep 2009 19:17:37 GMT (6kb)

Title: Effective Potential from the Effective-Range Expansion at Zero-Crossing
   in a Two-Channel Feshbach Model
Authors: N. T. Zinner
Categories: cond-mat.quant-gas cond-mat.stat-mech
Comments: 3 pages, no figures
   We consider a two-channel Feshbach model and determine the effective-range
expansion. While this expansion is badly behaved when the scattering length
goes to zero, we demonstate that effective potentials based on the lowest order
terms agree with those obtained from the full T-matrix. This result holds for
the low momenta of atoms in a Bose-Einstein condensate experiment. We find that
the temperature regime where the effective potential obtained is valid is
safely inside that of typical experiments.
\\ ( http://arxiv.org/abs/0909.1314 , 6kb)
Date: Mon, 7 Sep 2009 04:11:05 GMT (27kb)

Title: Critical Velocities for Roton and Super-Flow Quantum Turbulence in
   Liquid $^4$He
Authors: V. I. Kruglov
Categories: cond-mat.other cond-mat.supr-con
Comments: It is submitted to Physical Review Letters
   Two different types of transitions of the superfluid $^4$He to quantum
turbulence regimes are studied for $1{\rm D}$ geometry in the case when the
influence of the normal fluid on superfluid flow is suppressed. It is shown
that the roton mechanism of transition to quantum turbulence leads to a
critical velocity satisfying the relation $v_c\propto d^{-1/4}$. In the
super-flow mechanism, the transition to quantum turbulence arises when the
"quantum Reynolds number" is about $10^3$ and the critical velocity depends on
channel size $d$ as $v_c\propto d^{-1}$ in agreement with the equations of
motion for a superfluid component of the liquid $^4$He being disturbed by small
fluctuations of the normal fluid.
\\ ( http://arxiv.org/abs/0909.1140 , 27kb)
arXiv:0909.1228 (*cross-listing*)
Date: Mon, 7 Sep 2009 11:58:07 GMT (176kb)

Title: Kadath: a spectral solver for theoretical physics
Authors: Philippe Grandclement (LUTH)
Categories: gr-qc hep-th physics.comp-ph
Comments: Submitted to Journal of Computational Physics
   Kadath is a library that implements spectral methods in a very modular
manner. It is designed to solve a wide class of problems that arise in the
context of theoretical physics. Several types of coordinates are implemented
and additional geometries can be easily encoded. Partial differential equations
of various types are discretized by means of spectral methods. The resulting
system is solved using a Newton-Raphson iteration. Doing so, Kadath is able to
deal with strongly non-linear situations. The algorithms are validated by
applying the library to four different problems of contemporary physics, in the
fields of gauge field theory and general relativity
\\ ( http://arxiv.org/abs/0909.1228 , 176kb)
Date: Tue, 8 Sep 2009 20:47:33 GMT (35kb)

Title: Interaction Quenches of Fermi Gases
Authors: G\"otz S. Uhrig
Categories: cond-mat.str-el cond-mat.quant-gas
Comments: 4 pages, 2 figures
   It is shown that the jump in the momentum distribution of Fermi gases evolves
smoothly for small and intermediate times once an interaction between the
fermions is suddenly switched on. The jump does not vanish abruptly. The loci
in momentum space where the jumps occur are those of the noninteracting Fermi
sea. No relaxation of the Fermi surface geometry takes place.
\\ ( http://arxiv.org/abs/0909.1553 , 35kb)
Date: Tue, 8 Sep 2009 14:42:22 GMT (57kb)

Title: Anomalous Exciton-Condensation in Graphene Bilayers
Authors: Yafis Barlas, Rene C\^ot\'e, J. Lambert and A. H. MacDonald
Categories: cond-mat.mes-hall
Comments: 4 pages, 1 figure
   In ordinary semiconductor bilayers, exciton condensates appear at total
Landau level filling factor $\nu_{T}=1$. We predict that similar states will
occur in Bernal stacked graphene bilayers at many non-zero integer filling
factors. For $\nu_{T} = -3,1$ we find that the superfluid density of the
exciton condensate vanishes and that a finite-temperature fluctuation induced
first order isotropic-smectic phase transition occurs when the layer densities
are not balanced. These anomalous properties of bilayer graphene exciton
condensates are due to the degeneracy of Landau levels with $n=0$ and $n=1$
orbital character.
\\ ( http://arxiv.org/abs/0909.1502 , 57kb)
Date: Tue, 8 Sep 2009 05:02:54 GMT (16kb)

Title: Wigner distributions for finite state systems without redundant phase
   point operators
Authors: S. Chaturvedi, N. Mukunda and R.Simon
Categories: quant-ph
Comments: Latex, 14 pages
   We set up Wigner distributions for $N$ state quantum systems following a
Dirac inspired approach. In contrast to much of the work on this case,
requiring a $2N\times 2N$ phase space, particularly when $N$ is even, our
approach is uniformly based on an $N\times N $ phase space grid and thereby
avoids the necessity of having to invoke a `quadrupled' phase space and hence
the attendant redundance. Both $N$ odd and even cases are analysed in detail
and it is found that there are striking differences between the two. While the
$N$ odd case permits full implementation of the marginals property, the even
case does so only in a restricted sense. This has the consequence that in the
even case one is led to several equally good definitions of the Wigner
distributions as opposed to the odd case where the choice turns out to be
\\ ( http://arxiv.org/abs/0909.1387 , 16kb)
Date: Tue, 8 Sep 2009 11:43:29 GMT (184kb)

Title: Low velocity limits of cold atom clocks
Authors: J. Mu\~noz, I. Lizuain, J. G. Muga
Categories: quant-ph
Comments: 7 pages, 5 figures
Journal-ref: Phys. Rev. A 80, 022116 (2009)
   Fundamental low-energy limits to the accuracy of quantum clock and stopwatch
models in which the clock hand motion is activated by the presence of a
particle in a region of space have been studied in the past, but their
relevance for actual atomic clocks had not been assessed. In this work we
address the effect of slow atomic quantum motion on Rabi and Ramsey resonance
fringe patterns, as a perturbation of the results based on classical atomic
motion. We find the dependence of the fractional error of the corresponding
atomic clocks on the atomic velocity and interaction parameters.
\\ ( http://arxiv.org/abs/0909.1465 , 184kb)
Date: Tue, 8 Sep 2009 20:05:44 GMT (24kb)

Title: Trap and population imbalanced two-component Fermi gas in the BEC limit
Authors: S. A. Silotri
Categories: cond-mat.quant-gas cond-mat.supr-con
Comments: 5 pages, 5 figures
   We study equal mass population imbalanced two-component atomic Fermi gas with
unequal trap frequencies $(\omega_{\uparrow} \neq \omega_{\downarrow})$ at zero
temperature using the local density approximation (LDA). We consider the
strongly attracting Bose-Einstein condensation (BEC) limit where polarized
(gapless) superfluid is stable. The system exhibits shell structure:
unpolarized SF$\to$polarized SF$\to$normal N. Compared to trap symmetric case,
when the majority component is tightly confined the gapless superfluid shell
grows in size leading to reduced threshold polarization to form polarized
(gapless) superfluid core. In contrast, when the minority component is tightly
confined, we find that the superfluid phase is dominated by unpolarized
superfluid phase with gapless phase forming a narrow shell. The shell radii for
various phases as a function of polarization at different values of trap
asymmetry are presented and the features are explained using the phase diagram.
\\ ( http://arxiv.org/abs/0909.1561 , 24kb)
Date: Tue, 8 Sep 2009 14:12:31 GMT (859kb)

Title: Direct observation of a magnetic Bose glass
Authors: Tao Hong, A. Zheludev, H. Manaka, and L.-P. Regnault
Categories: cond-mat.str-el
Comments: 4 pages, 3 figures
   We report the single crystal study of the bulk magnetization and neutron
scattering measurements on a quantum S=1/2 spin ladders system
IPA-Cu(Cl0.95Br0.05)3with quenched disorder. In zero field, the disordered spin
liquid phase is preserved as in pure IPA-CuCl3. Due to the bond randomness, a
novel Bose glass phase was directly observed in Hc<H<H', which separates the
spin liquid phase from the unconventional Bose-Einstein condensation phase. The
observed finite value of boson compressibility dM/dH and lack of field-induced
three-dimensional long range order are consistent with the theoretical
\\ ( http://arxiv.org/abs/0909.1496 , 859kb)
arXiv:0909.1469 (*cross-listing*)
Date: Tue, 8 Sep 2009 12:00:08 GMT (399kb)

Title: Towards Quantum Superposition of Living Organisms
Authors: Oriol Romero-Isart, Mathieu L. Juan, Romain Quidant, J. Ignacio Cirac
Categories: quant-ph cond-mat.mes-hall
Comments: 8 pages, 4 figures
   The most striking feature of quantum mechanics is the existence of
superposition states, where an object appears to be in different situations at
the same time. Up to now, the existence of such states has been tested with
small objects, like atoms, ions, electrons and photons, and even with
molecules. Recently, it has been even possible to create superpositions of
collections of photons, atoms, or Cooper pairs. Current progress in
optomechanical systems may soon allow us to create superpositions of even
larger objects, like micro-sized mirrors or cantilevers, and thus to test
quantum mechanical phenomena at larger scales. Here we propose a method to cool
down and create quantum superpositions of the motion of sub-wavelength,
arbitrarily shaped dielectric objects trapped inside a high--finesse cavity at
a very low pressure. Our method is ideally suited for the smallest living
organisms, such as viruses, which survive under low vacuum pressures, and
optically behave as dielectric objects. This opens up the possibility of
testing the quantum nature of living organisms by creating quantum
superposition states in very much the same spirit as the original
Schr\"odinger's cat "gedanken" paradigm. We anticipate our essay to be a
starting point to experimentally address fundamental questions, such as the
role of life in quantum mechanics, and differences between many-world and
Copenhagen interpretations.
\\ ( http://arxiv.org/abs/0909.1469 , 399kb)
Date: Wed, 9 Sep 2009 19:38:48 GMT (81kb)

Title: Magnetic phase diagram of a spin-1 condensate in two dimensions with
   dipole interaction
Authors: Jonas A. Kj\"all, Andrew M. Essin and Joel E. Moore
Categories: cond-mat.quant-gas
Comments: 10 pages, 7 figures
   Several new features arise in the ground-state phase diagram of a spin-1
condensate trapped in an optical trap when the magnetic dipole interaction
between the atoms is taken into account along with confinement and spin
precession. The boundaries between the regions of ferromagnetic and polar
phases move as the dipole strength is varied and the ferromagnetic phases can
be modulated. The magnetization of the ferromagnetic phase perpendicular to the
field becomes modulated as a helix winding around the magnetic field direction,
with a wavelength inversely proportional to the dipole strength. This
modulation should be observable for current experimental parameters in
$^{87}$Rb. Hence the much-sought supersolid state, with broken continuous
translation invariance in one direction and broken global U(1) invariance,
occurs generically as a metastable state in this system as a result of dipole
interaction. The ferromagnetic state parallel to the applied magnetic field
becomes striped in a finite system at strong dipolar coupling.
\\ ( http://arxiv.org/abs/0909.1751 , 81kb)
Date: Wed, 9 Sep 2009 11:35:41 GMT (279kb,D)

Title: Nonequilibrium dynamics of vortex arrest in a finite temperature
   Bose-Einstein condensate
Authors: T. M. Wright, A. S. Bradley, R. J. Ballagh
Categories: cond-mat.quant-gas
Comments: 9 pages, 6 figures
   We perform finite temperature dynamical simulations of the arrest of a
rotating Bose-Einstein condensate by a fixed trap anisotropy, using a
Hamiltonian classical-field method. We consider a quasi-two-dimensional
condensate containing a single vortex in equilibrium with a rotating thermal
cloud. Introducing an elliptical deformation of the trapping potential leads to
the loss of angular momentum from the system. We identify the condensate and
the complementary thermal component of the nonequilibrium field, and compare
the evolution of their angular momenta and angular velocities. By varying the
trap anisotropy we alter the relative efficiencies of the vortex-cloud and
cloud-trap coupling. For strong trap anisotropies the angular momentum of the
thermal cloud may be entirely depleted before the vortex begins to decay. For
weak trap anisotropies, the thermal cloud exhibits a long-lived steady state in
which it rotates at an intermediate angular velocity.
\\ ( http://arxiv.org/abs/0909.1683 , 279kb)
Date: Wed, 9 Sep 2009 14:23:49 GMT (419kb)

Title: Effects of interaction on the diffusion of atomic matter waves in
   one-dimensional quasi-periodic potentials
Authors: Marco Larcher, Franco Dalfovo, Michele Modugno
Categories: cond-mat.quant-gas
   We study the behaviour of an ultracold atomic gas of bosons in a bichromatic
lattice, where the weaker lattice is used as a source of disorder. We
numerically solve a discretized mean-field equation, which generalizes the
one-dimensional Aubry-Andr\`e model for particles in a quasi-periodic potential
by including the interaction between atoms. We compare the results for
commensurate and incommensurate lattices. We investigate the role of the
initial shape of the wavepacket as well as the interplay between two competing
effects of the interaction, namely self-trapping and delocalization. Our
calculations show that, if the condensate initially occupies a single lattice
site, the dynamics of the interacting gas is dominated by self-trapping in a
wide range of parameters, even for weak interaction. Conversely, if the
diffusion starts from a Gaussian wavepacket, self-trapping is significantly
suppressed and the destruction of localization by interaction is more easily
\\ ( http://arxiv.org/abs/0909.1714 , 419kb)
Date: Wed, 9 Sep 2009 09:49:14 GMT (166kb)

Title: Matter-wave dark solitons: stochastic vs. analytical results
Authors: S.P. Cockburn, H.E. Nistazakis, T.P. Horikis, P.G. Kevrekidis, N.P.
   Proukakis, D.J. Frantzeskakis
Categories: cond-mat.quant-gas cond-mat.other
Comments: 4 pages, 3 figures
   The dynamics of dark matter-wave solitons in elongated atomic condensates are
discussed at finite temperatures. Simulations with the stochastic
Gross-Pitaevskii equation reveal a noticeable, experimentally observable spread
in individual soliton trajectories, attributed to inherent fluctuations in both
phase and density of the underlying medium. Averaging over a number of such
trajectories (as done in experiments) washes out such background fluctuations,
revealing a well-defined temperature-dependent temporal growth in the
oscillation amplitude. The average soliton dynamics is well captured by the
simpler dissipative Gross-Pitaevskii equation, both numerically and via an
analytically-derived equation for the soliton center based on perturbation
theory for dark solitons.
\\ ( http://arxiv.org/abs/0909.1660 , 166kb)
Date: Wed, 9 Sep 2009 22:56:32 GMT (1343kb)

Title: A Superglass Phase of Interacting Bosons
Authors: Ka-Ming Tam, Scott Geraedts, Stephen Inglis, Michel J. P. Gingras and
   Roger G. Melko
Categories: cond-mat.dis-nn
Comments: 5 pages 3 figures
   Despite the simplicity of its constituent atoms, the phase diagram of bulk
helium has proven to be compelling and controversial -- especially in light of
recent observations of supersolid behavior in the crystal phase of Helium-4.
Several experiments have shown that superflow is enhanced by imperfections in
the crystal lattice, such as roaming defects and interstitial atoms. Most
strikingly, new experiments by Davis and collaborators have suggested that the
onset of superflow is intimately tied to relaxation dynamics characteristic of
glassy, or amorphous, solids. In this work, we examine the relationship between
superflow and glassiness in a boson lattice model, and demonstrate that simple
random disordered interactions can promote a stable superglass phase in a
system of Bose particles. In this superglass, superflow and glassy density
localization coexist in equilibrium without exhibiting phase separation.
\\ ( http://arxiv.org/abs/0909.1845 , 1343kb)
Date: Wed, 9 Sep 2009 08:33:21 GMT (22kb)

Title: Partition function of a bubble formed in double stranded DNA
Authors: Yashwant Singh
Categories: cond-mat.soft cond-mat.stat-mech
Comments: 9 Pages, 1 figure. Submitted to Euro. Phys. Letter on 16th July 2009
   We calculate the entropic part of partition function of a bubble embedded in
a double stranded DNA (dsDNA) by considering the total weights of possible
configurations of a system of two single stranded DNA (ssDNA) of given length
which start from a point along the contour of dsDNA and reunite at a position
vector {\bf r} measured from the first point and the distribution function of
the position vector {\bf r} which separates the two zipper forks of the bubble
in dsDNA. For the distribution function of position vector {\bf r} we use the
distribution of the end-to-end vector {\bf r} of strands of given length of
dsDNA found from the wormlike chain model. We show that when the chains forming
the bubble are assumed to be Gaussian the so called loop closure exponent $c$
is 3 and when we made correction by including self avoidence in each chain the
value of $c$ becames 3.2.
\\ ( http://arxiv.org/abs/0909.1649 , 22kb)
Date: Thu, 10 Sep 2009 13:52:02 GMT (179kb)

Title: A multi-photon magneto-optical trap
Authors: Saijun Wu, Thomas Plisson, Roger Brown, William D. Phillips and J. V.
Categories: physics.atom-ph
Comments: 10 pages, 5 figures
   We demonstrate a Magneto-Optical Trap (MOT) configuration which employs
optical forces due to light scattering between electronically excited states of
the atom. With the standard MOT laser beams propagating along the {\it x}- and
{\it y}- directions, the laser beams along the {\it z}-direction are at a
different wavelength that couples two sets of {\it excited} states. We
demonstrate efficient cooling and trapping of cesium atoms in a vapor cell and
sub-Doppler cooling on both the red and blue sides of the two-photon resonance.
The technique demonstrated in this work may have applications in
background-free detection of trapped atoms, and in assisting laser-cooling and
trapping of certain atomic species that require cooling lasers at inconvenient
\\ ( http://arxiv.org/abs/0909.1949 , 179kb)
Date: Thu, 10 Sep 2009 14:25:07 GMT (140kb)

Title: Cavity QED nondemolition measurement scheme using quantized atomic
Authors: Jonas Larson and Mahmoud Abdel-Aty
Categories: quant-ph
Comments: 7 pages, 7 figures
   Considering ultracold atoms traversing a high-Q Fabry-Perot cavity, we
theoretically demonstrate a quantum nondemolition measurement of the photon
number. This fully quantum mechanical approach may be understood utilizing
concepts as effective mass and group velocity of the atom. The various photon
numbers induce a splitting of the atomic wave packet, and a time-of-flight
measurement of the atom thereby reveals the photon number. While repeated
atomic measurements increase the efficiency of the protocol, it is shown that
by considering long interaction times only a few atoms are needed to resolve
the photon number with almost perfect accuracy.
\\ ( http://arxiv.org/abs/0909.1958 , 140kb)

Date: Thu, 10 Sep 2009 09:09:03 GMT (186kb)

Title: Finite-temperature phase transitions in quasi-two-dimensional spin-1
   Bose gases
Authors: Ville Pietil\"a, Mikko M\"ott\"onen, and Tapio P. Simula
Categories: cond-mat.quant-gas
Comments: 4 pages, 3 figures
   Recently, the Berezinskii-Kosterlitz-Thouless transition was found to be
mediated by half-quantum vortices (HQVs) in two-dimensional (2D)
antiferromagnetic Bose gases [Phys. Rev. Lett. 97, 120406 (2006)]. We study the
thermal activation of HQVs in the experimentally relevant trapped quasi-2D
systems and find that the crossover temperature is shifted upwards if skyrmions
are allowed. Above the defect binding temperatures we observe transitions
corresponding to the onset of a coherent condensate and a quasi-condensate and
discuss the absence of a fragmented condensate.
\\ ( http://arxiv.org/abs/0909.1898 , 186kb)
Date: Thu, 10 Sep 2009 05:45:24 GMT (2163kb)

Title: Transition from Band insulator to Bose-Einstein Condensate superfluid
   and Mott State of Cold Fermi Gases with Multiband Effects in Optical Lattices
Authors: Ryota Watanabe and Masatoshi Imada
Categories: cond-mat.quant-gas cond-mat.other
Comments: 13 pages, 10 figures
   We study two models realized by two-component Fermi gases loaded in optical
lattices. We clarify that multi-band effects inevitably caused by the optical
lattices generate a rich structure, when the systems crossover from the region
of weakly bound molecular bosons to the region of strongly bound atomic bosons.
Here the crossover can be controlled by attractive fermion interaction. One of
the present models is a case with attractive fermion interaction, where an
insulator-superfluid transition takes place. The transition is characterized as
the transition between a band insulator and a Bose-Einstein condensate (BEC)
superfluid state. Differing from the conventional BCS superfluid transition,
this transition shows unconventional properties. In contrast to the one
particle excitation gap scaled by the superfluid order parameter in the
conventional BCS transition, because of the multi-band effects, a large gap of
one-particle density of states is retained all through the transition although
the superfluid order grows continuously from zero. A reentrant transition with
lowering temperature is another unconventionality. The other model is the case
with coexisting attractive and repulsive interactions. Within a mean field
treatment, we find a new insulating state, an orbital ordered insulator. This
insulator is one candidate for the Mott insulator of molecular bosons and is
the first example that the orbital internal degrees of freedom of molecular
bosons appears explicitly. Besides the emergence of a new phase, a coexisting
phase also appears where superfluidity and an orbital order coexist just by
doping holes or particles. The insulating and superfluid particles show
differentiation in momentum space as in the high-Tc cuprate superconductors.
\\ ( http://arxiv.org/abs/0909.1871 , 2163kb)

The replacements:

replaced with revised version Fri, 4 Sep 2009 07:06:56 GMT (123kb)

Title: Strong interaction regime of the nonlinear Landau-Zener problem for
   photo- and magneto-association of cold atoms
Authors: R. Sokhoyan, H. Azizbekyan, C. Leroy, and A. Ishkhanyan
Categories: cond-mat.quant-gas
Comments: submitted to JETP (13 pages, 4 figures)
\\ ( http://arxiv.org/abs/0909.0625 , 123kb)
replaced with revised version Fri, 4 Sep 2009 07:21:43 GMT (146kb)

Title: Dispersion Management of Ultraslow Light in a Bose-Einstein Condensate
   via Trap Curvature
Authors: Devrim Tarhan, Seckin Sefi, and Ozgur E. Mustecaplioglu
Categories: physics.optics cond-mat.quant-gas quant-ph
Comments: 14 pages, 3 figures, some comments are added and the title of the
   article is changed
\\ ( http://arxiv.org/abs/0905.3541 , 146kb)
replaced with revised version Mon, 7 Sep 2009 18:31:30 GMT (538kb,D)

Title: Perturbation theory for the Nonlinear Schroedinger Equation with a
   random potential
Authors: Shmuel Fishman, Yevgeny Krivolapov and Avy Soffer
Categories: cond-mat.dis-nn
Comments: 30 pages, 7 figures, accepted to Nonlinearity
\\ ( http://arxiv.org/abs/0901.4951 , 538kb)
replaced with revised version Mon, 7 Sep 2009 07:13:48 GMT (556kb)

Title: Simulating dense QCD matter with ultracold atomic boson-fermion mixtures
Authors: Kenji Maeda, Gordon Baym, and Tetsuo Hatsuda
Categories: cond-mat.quant-gas hep-ph nucl-th
Comments: 4 pages, 3 figures
Report-no: TKYNT-09-09
Journal-ref: Phys.Rev.Lett. 103, 085301 (2009)
\\ ( http://arxiv.org/abs/0904.4372 , 556kb)
replaced with revised version Tue, 8 Sep 2009 08:09:57 GMT (74kb)

Title: Propagation of Second sound in a superfluid Fermi gas in the unitary
Authors: Emiko Arahata and Tetsuro Nikuni
Categories: cond-mat.quant-gas cond-mat.other
Comments: 15 pages, 8 figures
\\ ( http://arxiv.org/abs/0907.2743 , 74kb)
replaced with revised version Tue, 8 Sep 2009 11:07:00 GMT (1418kb,D)

Title: A pump-probe study of the formation of rubidium molecules by ultrafast
   photoassociation of ultracold atoms
Authors: David J. McCabe, Duncan G. England, Hugo E. L. Martay, Melissa E.
   Friedman, Jovana Petrovic, Emiliya Dimova, B\'eatrice Chatel and Ian A.
Categories: physics.chem-ph physics.atom-ph physics.optics
Comments: Accepted for publication in Phys. Rev. A (10 pages, 9 figures)
Journal-ref: Phys. Rev. A 80, 033404 (2009)
DOI: 10.1103/PhysRevA.80.033404
\\ ( http://arxiv.org/abs/0904.0244 , 1418kb)
replaced with revised version Tue, 8 Sep 2009 12:24:20 GMT (2895kb)

Title: Demonstrating coherent control in 85Rb2 using ultrafast laser pulses: a
   theoretical outline of two experiments
Authors: Hugo E. L. Martay, David J. McCabe, Duncan G. England, Melissa E.
   Friedman, Jovana Petrovic, and Ian A. Walmsley
Categories: physics.atom-ph physics.chem-ph
Comments: 8 pages, 9 figures, PRA, 80, 033403 (2009)
Journal-ref: Phys. Rev. A, 80, 033403 (2009)
DOI: 10.1103/PhysRevA.80.033403
\\ ( http://arxiv.org/abs/0904.0225 , 2895kb)
replaced with revised version Tue, 8 Sep 2009 21:01:13 GMT (95kb)

Title: Quantum mechanics in phase space: First order comparison between the
   Wigner and the Fermi function
Authors: G. Benenti, G. Strini
Categories: quant-ph
Comments: 5 pages, 3 figures, added new data and discussion
\\ ( http://arxiv.org/abs/0906.0925 , 95kb)
replaced with revised version Wed, 9 Sep 2009 13:11:20 GMT (171kb,D)

Title: Rayleigh-Taylor instability of binary condensates in axis symmetric
Authors: S. Gautam and D. Angom
Categories: cond-mat.quant-gas
Comments: 4 pages, 3figures
\\ ( http://arxiv.org/abs/0908.4336 , 171kb)
arXiv:0812.5073 (*cross-listing*)
replaced with revised version Wed, 9 Sep 2009 13:19:04 GMT (3272kb)

Title: Bright and dark solitons in Bose-Einstein condensates
Authors: S. Rajendran, P. Muruganandam, M. Lakshmanan
Categories: nlin.PS cond-mat.other nlin.SI
Comments: 30 pages, 19 figures, 4 tables
\\ ( http://arxiv.org/abs/0812.5073 , 3272kb)
replaced with revised version Wed, 9 Sep 2009 01:32:30 GMT (1329kb)

Title: Supersolidity of cold-atom Bose-Fermi mixtures in optical lattices
Authors: Peter P. Orth, Doron L. Bergman, and Karyn Le Hur
Categories: cond-mat.quant-gas
Comments: Moved technical details to appendices. Enlarged list of references.
   Corrected typos, new Figs.11 and 15. Final and published version
Journal-ref: Phys. Rev. A 80, 023624 (2009)
DOI: 10.1103/PhysRevA.80.023624
\\ ( http://arxiv.org/abs/0905.1125 , 1329kb)

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,                  mdavis_at_physics.uq.edu.au
Australia.                           www.physics.uq.edu.au/people/mdavis/
Matt's arXiv selection: weekly summary of cold-atom papers from arXiv.org
Legal stuff: Unless stated otherwise, this e-mail represents only the
views of the sender and not the views of the University of Queensland
Matts-arxiv mailing list
Received on Fri Nov 20 2009 - 18:56:16 EST

This archive was generated by hypermail 2.2.0 : Fri Nov 20 2009 - 18:56:35 EST