Matt's arXiv selection: week ending 25 April 2008.

From: Matthew Davis <>
Date: Thu, 08 May 2008 08:27:56 +1000

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

Dear subscribers,

There is currently a vacancy for a tenured faculty member in the field of
theoretical quantum atom optics at the University of Queensland (my
institution). Applications close on June 16, 2008. The full details can be
found here:

Onto the usual business: week there are 34 new preprints and 18 replacements.

Date: Thu, 17 Apr 2008 20:49:38 GMT (878kb)

Title: Bose-Einstein condensates in disordered potentials
Authors: Leonardo Fallani, Chiara Fort and Massimo Inguscio
Categories: cond-mat.dis-nn
Comments: 43 pages, 17 figures, to be published in "Advances in Atomic,
   Molecular, and Optical Physics"
   The interplay between disorder and interactions is a "leit-motiv" of
condensed matter physics, since it constitutes the driving mechanism of the
metal-insulator transition. Bose-Einstein condensates in optical potentials are
proving to be powerful tools to quantum simulate disordered systems. We will
review the main experimental and theoretical results achieved in the last few
years in this rapidly developing field.
\\ ( , 878kb)
Date: Thu, 17 Apr 2008 20:10:04 GMT (17kb)

Title: Optimal non-linear passage through a quantum critical point
Authors: Roman Barankov and Anatoli Polkovnikov
Categories: cond-mat.other
Comments: 4+ pages, 2 figures
   We analyze the problem of optimal adiabatic passage through a quantum
critical point. We show that to minimize the number of defects the tuning
parameter should be changed as a power-law in time. The optimal power is
proportional to the logarithm of the total passage time multiplied by universal
critical exponents characterizing the phase transition. We support our results
by the general scaling analysis and by explicit calculations for the transverse
field Ising model.
\\ ( , 17kb)
Date: Thu, 17 Apr 2008 22:25:21 GMT (971kb)

Title: Preparing a highly degenerate Fermi gas in an optical lattice
Authors: J. R. Williams, J. H. Huckans, R. W. Stites, E. L. Hazlett, and K. M.
Categories: cond-mat.stat-mech cond-mat.other
Comments: 5 pages, 4 figures
   We propose a method to prepare a sample of fermionic atoms in a
three-dimensional (3D) optical lattice at unprecedentedly low temperatures and
uniform filling factors. The process involves adiabatic loading of atoms into
multiple energy bands of an optical lattice followed by a filtering stage
whereby atoms from all but the ground band are removed. Of critical importance
is the use of a non-harmonic trapping potential, taken here to be the radial
profile of a high-order Laguerre-Gaussian laser beam, to provide external
confinement for the atoms. For realistic experimental parameters, this
procedure should produce samples with temperatures $\sim10^{-3}$ of the Fermi
temperature. This would allow the investigation of the low-temperature phase
diagram of the Fermi-Hubbard model as well as the initialization of a
high-fidelity quantum register.
\\ ( , 971kb)
Date: Fri, 18 Apr 2008 10:45:51 GMT (12kb)

Title: Quantum kinetic theory for the collapse of Bose-Einstein condensate
Authors: Shyamal Biswas
Categories: cond-mat.stat-mech
Comments: 3 pages, 1 figure
   We show how to apply the quantum kinetic theory in an inhomogeneous system
like harmonically trapped Bose condensate. We calculate the temperature
dependence of the critical number of particles by a quantum kinetic theory
within the Hartree-Fock approximation and find that there is a dramatic
increase in the critical number of particles as the condensation point is
approached. Our results support the experimental result which was obtained well
below the condensation temperature. The nature of the temperature dependence of
the critical number obtained from the quantum kinetic theory is the same as
obtained from the scaling theory.
\\ ( , 12kb)
Date: Fri, 18 Apr 2008 13:57:03 GMT (138kb)

Title: Quantum reflection: The invisible quantum barrier
Authors: J. X. de Carvalho, M. S. Hussein, and Weibin Li
Categories: cond-mat.other
Comments: 13pages, 6figures
   We construct the invisible quantum barrier which represents the phenomenon of
quantum reflection using the available data. We use the Abel equation to invert
the data. The resulting invisible quantum barrier is double-valued in both
axes. We study this invisible barrier in the case of atom and Bose-Einstein
Condensate reflection from a solid silicon surface. A time-dependent,
one-spatial dimension Gross-Pitaevskii equation is solved for the BEC case. We
found that the BEC behaves very similarly to the single atom except for size
effects, which manifest themselves in a maximum in the reflectivity at small
distances from the wall. The effect of the atom-atom interaction on the BEC
reflection and correspondingly on the invisible barrier is found to be
appreciable at low velocities and comparable to the finite size effect. The
trapping of ultracold atom or BEC between two walls is discussed.
\\ ( , 138kb)
Date: Fri, 18 Apr 2008 14:28:10 GMT (125kb)

Title: Quantum Dynamics in the Thermodynamic Limit
Authors: Jasper van Wezel
Categories: cond-mat.other cond-mat.str-el
Comments: 13 pages, 4 figures
   The description of spontaneous symmetry breaking that underlies the
connection between classically ordered objects in the thermodynamic limit and
their individual quantum mechanical building blocks is one of the cornerstones
of modern condensed matter theory and has found applications in many different
areas of physics. The theory of spontaneous symmetry breaking however, is
inherently an equilibrium theory, which does not address the dynamics of
quantum systems in the thermodynamic limit. Here, we will use the example of a
particular antiferromagnetic model system to show that the presence of a
so-called thin spectrum of collective excitations with vanishing energy -one of
the well-known characteristic properties shared by all symmetry-breaking
objects- can allow these objects to also spontaneously break time-translation
symmetry in the thermodynamic limit. As a result, that limit is found to be
able, not only to reduce quantum mechanical equilibrium averages to their
classical counterparts, but also to turn individual-state quantum dynamics into
classical physics. In the process, we find that the dynamical description of
spontaneous symmetry breaking can also be used to shed some light on the
possible origins of Born's rule. We conclude by describing an experiment on a
condensate of exciton polaritons which could potentially be used to
experimentally test the proposed mechanism.
\\ ( , 125kb)
Date: Fri, 18 Apr 2008 15:28:55 GMT (11kb)

Title: Effect of anisotropic hopping on the Bose Hubbard model phase diagram:
   strong-coupling perturbation theory on a square lattice
Authors: J. K. Freericks (Georgetown University)
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: (5 pages, 1 figure, RevTeX)
   There has been a recent resurgence of experimental efforts to quantitatively
determine the phase diagram of the Bose Hubbard model by carefully analyzing
experiments with ultracold bosonic atoms on an optical lattice. In many
realizations of these experiments, the hopping amplitudes are not homogeneous
throughout the lattice, but instead, the lattice has an anisotropy where
hopping along one direction is not exactly equal to hopping along a
perpendicular direction. In this contribution, we examine how an anisotropy in
the hopping matrix elements affects the Mott lobes of the Bose Hubbard model.
For weak anisotropy, we find the phase diagram is only slightly modified when
expressed in terms of the average hopping, while for strong anisotropy, one
expects to ultimately see dimensional crossover effects.
\\ ( , 11kb)
Date: Fri, 18 Apr 2008 19:20:35 GMT (38kb,D)

Title: Teaching superfluidity at the introductory level
Authors: Alexander J.M. Schmets and Wouter Montfrooij
Categories: cond-mat.supr-con physics.ed-ph quant-ph
Comments: This paper was written to compensate for the lack of any useful
   treatment of superfluidity in standard (introduction) modern physics
   textbooks. The paper contains some interesting estimates that might be of
   interest to people involved in superfluid research
   Standard introductory modern physics textbooks do not exactly dwell on
superfluidity in 4He. Typically, Bose-Einstein condensation (BEC) is mentioned
in the context of an ideal Bose gas, followed by the statement that BEC happens
in 4He and that the ground state of 4He exhibits many interesting properties
such as having zero viscosity. Not only does this approach not explain in any
way why 4He becomes a superfluid, it denies students the opportunity to learn
about the far reaching consequences of energy gaps as they develop in both
superfluids and superconductors. We revisit superfluid 4He by starting with
Feynman's explanation of superfluidity based on Bose statistics as opposed to
BEC, and we present exercises for the students that allow them to arrive at a
very accurate estimate of the superfluid transition temperature and of the
energy gap separating the ground state from the first excited state. This paper
represents a self-contained account of superfluidity, which can be covered in
one or two lessons in class.
\\ ( , 38kb)
Date: Thu, 17 Apr 2008 23:28:03 GMT (674kb,D)

Title: Quantum control of the hyperfine-coupled electron and nuclear spins in
   alkali atoms
Authors: Seth T. Merkel. Poul S. Jessen, Ivan H. Deutsch
Categories: quant-ph
Comments: 14 pages, 7 figures
   We study quantum control of the full hyperfine manifold in the
ground-electronic state of alkali atoms based on applied radio frequency and
microwave fields. Such interactions should allow essentially decoherence-free
dynamics and the application of techniques for robust control developed for NMR
spectroscopy. We establish the conditions under which the system is
controllable in the sense that one can generate an arbitrary unitary on the
system. We apply this to the case of $^{133}$Cs with its $d=16$ dimensional
Hilbert space of magnetic sublevels in the $6S_{1/2}$ state, and design control
waveforms that generate an arbitrary target state from an initial fiducial
state. We develop a generalized Wigner function representation for this space
consisting of the direct sum of two irreducible representation of SU(2),
allowing us to visualize these states. The performance of different control
scenarios is evaluated based on the ability to generate high-fidelity operation
in an allotted time with the available resources. We find good operating points
commensurate with modest laboratory requirements.
\\ ( , 674kb)
Date: Fri, 18 Apr 2008 12:02:59 GMT (73kb,D)

Title: Quantum Interface for Nanomechanics and Atomic Ensembles
Authors: K. Hammerer, M.Aspelmeyer, E.S. Polzik, P. Zoller
Categories: quant-ph
   We suggest to interface atomic ensembles, for which means of high precision
state preparation, manipulation and measurement are available, via an optical
quantum bus to nanomechanical systems. This allows for a Quantum Non-Demolition
Bell measurement, projecting the coupled system atomic ensemble -
nanomechanical resonator into an entangled state. The entanglement is
observable even for nanoresonators initially well above their ground states and
can be utilized for teleportation of states from an atomic ensemble to the
mechanical system. Because of the rich toolbox already available for these
systems, we expect the interface to give rise to a variety of new quantum
\\ ( , 73kb)
Date: Fri, 18 Apr 2008 12:36:38 GMT (129kb)

Title: Theory of near-field matter wave interference beyond the eikonal
Authors: Stefan Nimmrichter, Klaus Hornberger
Categories: quant-ph
Comments: 19 pages, 10 figures
   A generalized description of Talbot-Lau interference with matter waves is
presented, which accounts for arbitrary grating interactions and realistic beam
characteristics. The dispersion interaction between the beam particles and the
optical elements strongly influences the interference pattern in this
near-field effect, and it is known to dominate the fringe visibility if
increasingly massive and complex particles are used. We provide a general
description of the grating interaction process by combining semiclassical
scattering theory with a phase space formulation. It serves to systematically
improve the eikonal approximation used so far, and to assess its regime of
\\ ( , 129kb)

Date: Fri, 18 Apr 2008 07:10:58 GMT (122kb)

Title: Potassium ground state scattering parameters and Born-Oppenheimer
   potentials from molecular spectroscopy
Authors: Stephan Falke, Horst Knoeckel, Jan Friebe, Matthias Riedmann, Eberhard
   Tiemann, Christian Lisdat
Categories: physics.atom-ph physics.atm-clus
Comments: 14 pages, 4 figures, 8 tables
   We present precision measurements with MHz uncertainty of the energy gap
between asymptotic and well bound levels in the electronic ground state X
$^1\Sigma_{\mathrm{g}}^+$ of the $^{39}$K$_2$ molecule. The molecules are
prepared in a highly collimated particle beam and are interrogated in a
$\Lambda$-type excitation scheme of optical transitions to long range levels
close to the asymptote of the ground state, using the electronically excited
state A $^1\Sigma^+_{\rm u}$ as intermediate one. The transition frequencies
are measured either by comparison with I$_2$ lines or by absolute measurements
using a fs-frequency comb. The determined level energies were used together
with Feshbach resonances from cold collisions of $^{39}$K and $^{40}$K reported
from other authors to fit new ground state potentials. Precise scattering
lengths are determined and tests of the validity of the Born-Oppenheimer
approximation for the description of cold collisions at this level of precision
are performed.
\\ ( , 122kb)

Date: Fri, 18 Apr 2008 13:21:39 GMT (77kb,D)

Title: Cross-Molecular Coupling in Combined Photoassociation and Feshbach
Authors: Matt Mackie, Matthew Fenty, Danielle Savage, and Jake Kesselman
Categories: physics.atom-ph physics.chem-ph
Comments: 4 pages, 2 figs, 22+ refs
   We examine combined photoassociation and Feshbach resonances in a
Bose-Einstein condensate, focusing on the case where only one field, magnetic
or laser, is off-resonant. For off-resonant magnetic fields, the position of
laser resonance is dispersively shifted with magnetic field, blue below the
Feshbach resonance, while atom losses to photoassociation cease at a specific
magnetic field and saturate at the limit for magnetoassociation alone. For
off-resonant lasers, a similar shift occurs in the position of magnetic-field
resonance, and a node occurs in Feshbach losses at a particular laser detuning;
however, in contrast to the photoassociation node, the position of the Feshbach
node depends on intensity. Cross coupling between the photoassociation and
Feshbach molecules, and associated quantum interference, is implicated as the
physical mechanism responsible for this behavior. Off-Feshbach-resonant results
agree reasonably with recent observations.
\\ ( , 77kb)

Date: Mon, 21 Apr 2008 11:45:50 GMT (66kb)

Title: Interband physics in an ultra-cold Fermi gas in an optical lattice
Authors: J.-P. Martikainen, E. Lundh, and T. Paananen
Categories: cond-mat.stat-mech cond-mat.supr-con
Comments: 4 pages, 2 figures
   We study a gas of strongly polarized cold fermions in an optical lattice when
the excited p-bands are populated. We derive the relevant Hamiltonian and
discuss the expected phase diagram for both repulsive and attractive
interactions. In the parameter regime covered here, checkerboard
anti-ferromagnetic ordering is found to be possible for repulsive interactions
while for attractive interactions, transitions between different types of
paired phases are predicted.
\\ ( , 66kb)

Date: Mon, 21 Apr 2008 12:25:48 GMT (647kb,D)

Title: Double barrier potentials for matter-wave gap solitons
Authors: V. Ahufinger, B. A. Malomed, G. Birkl, R. Corbalan and A. Sanpera
Categories: cond-mat.other
Comments: 5 pages, 4 figures
   We investigate collisions of solitons of the gap type, supported by a lattice
potential in repulsive Bose-Einstein condensates, with an effective
double-barrier potential that resembles a Fabry-Perot cavity. We identify
conditions under which the trapping of the entire incident soliton in the
cavity is possible. Collisions of the incident soliton with an earlier trapped
one are considered too. In the latter case, many outcomes of the collisions are
identified, including merging, release of the trapped soliton with or without
being replaced by the incoming one, and trapping of both solitons.
\\ ( , 647kb)

Date: Mon, 21 Apr 2008 19:05:26 GMT (43kb)

Title: A Unitary Fermi Supersolid: The Larkin-Ovchinnikov Phase
Authors: Aurel Bulgac and Michael McNeil Forbes
Categories: cond-mat.supr-con
Comments: 4 pages, 3 figures, RevTeX4
Report-no: NG-0809
   We present strong theoretical evidence that a Larkin-Ovchinnikov (LOFF/FFLO)
pairing phase is favoured over the homogeneous superfluid and normal phases in
three-dimensional unitary Fermi systems. Using a density functional theory
(DFT) based on the latest quantum Monte-Carlo calculations and experimental
results, we show that this phase is competitive over a large region of the
phase diagram. The oscillations in the number densities and pairing field have
a substantial amplitude, and a period some three to ten times the average
interparticle separation. Within the DFT, the transition to a normal polarized
Fermi liquid at large polarizations is smooth, while the transition to a
fully-paired superfluid is abrupt.
\\ ( , 43kb)

Date: Mon, 21 Apr 2008 17:37:39 GMT (231kb,D)

Title: Counting atoms using interaction blockade in an optical superlattice
Authors: P. Cheinet, S. Trotzky, M. Feld, U. Schnorrberger, M. Moreno-Cardoner,
   S. Foelling, I. Bloch
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We report on the observation of an interaction blockade effect for ultracold
atoms in optical lattices, analogous to Coulomb blockade observed in mesoscopic
solid state systems. When the lattice sites are converted into biased double
wells, we detect a discrete set of steps in the well population for increasing
bias potentials. These correspond to tunneling resonances where the atom number
on each side of the barrier changes one by one. This allows us to count and
control the number of atoms within a given well. By evaluating the amplitude of
the different plateaus, we can fully determine the number distribution of the
atoms in the lattice, which we demonstrate for the case of a superfluid and
Mott insulating regime of 87Rb.
\\ ( , 231kb)

Date: Mon, 21 Apr 2008 09:56:58 GMT (65kb)

Title: Spatial entanglement of paired photons generated in cold atomic
Authors: Clara I. Osorio, Sergio Barreiro, Morgan W. Mitchell and Juan P.
Categories: quant-ph
Comments: 5 pages, 3 figures, Submitted to Phys. Rev. A
   Cold atomic ensembles can mediate the generation of entanglement between
pairs of photons. Photons with specific directions of propagation are detected,
and the entanglement can reside in any of the degrees of freedom that describe
the whole quantum state of the photons: polarization, spatial shape or
frequency. We show that the direction of propagation of the generated photons
determines the spatial quantum state of the photons and therefore, the amount
of entanglement generated. When photons generated in different directions are
combined, this spatial distinguishing information can degrade the quantum
purity of the polarization or frequency entanglement.
\\ ( , 65kb)

Date: Mon, 21 Apr 2008 11:24:10 GMT (494kb,D)

Title: Giant electro-optic effect using polarizable dark states
Authors: A. K. Mohapatra, M. G. Bason, B. Butscher, K. J. Weatherill, and C. S.
Categories: quant-ph
   The electro-optic effect, where the refractive index of a medium is modified
by an electric field, is of central importance in non-linear optics, laser
technology, quantum optics and optical communications. In general,
electro-optic coefficients are very weak and a medium with a giant
electro-optic coefficient would have profound implications for non-linear
optics, especially at the single photon level, enabling single photon
entanglement and switching. Here we propose and demonstrate a giant
electro-optic effect based on polarizable dark states. We demonstrate phase
modulation of the light field in the dark state medium and measure an
electro-optic coefficient that is more than 12 orders of magnitude larger than
in other gases. This enormous Kerr non-linearity also creates the potential for
precision electrometry and photon entanglement.
\\ ( , 494kb)

Date: Mon, 21 Apr 2008 23:57:28 GMT (331kb,D)

Title: Dynamics of matter-wave solitons in a time-modulated two-dimensional
   optical lattice
Authors: Gennadiy Burlak, Boris A. Malomed
Categories: cond-mat.other
Comments: 22 pages, 9 figures
   By means of the variational approximation (VA) and systematic simulations, we
study dynamics and stability boundaries for solitons in a two-dimensional (2D)
self-attracting Bose-Einstein condensate (BEC), trapped in an optical lattice
(OL) whose amplitude is subjected to the periodic time modulation (the
modulation frequency, $\omega $, may be in the range of several KHz). Regions
of stability of the solitons against the collapse and decay are identified in
the space of the model's parameters. A noteworthy result is that the stability
limit may reach the largest (100%) modulation depth, and the collapse threshold
may exceed its classical value in the static lattice (which corresponds to the
norm of Townes soliton). Minimum norm $% N_{\min}$ necessary for the stability
of the solitons is identified too. It features a strong dependence on $\omega $
at a low frequencies, due to a resonant decay of the soliton. Predictions of
the VA are reasonably close to results of the simulations. In particular, the
VA helps to understand salient resonant features in the shape of the stability
boundaries observed with the variation of $\omega $.
\\ ( , 331kb)

Date: Tue, 22 Apr 2008 01:21:58 GMT (23kb)

Title: Quantum phases and phase transitions of interacting bosons in a Kagome
Authors: Jinwu Ye
Categories: cond-mat.str-el
Comments: 4+ pages, 3 figures, REVTEX4. This is a short version of
   cond-mat/0612009 which is under a substantial expansion
   By using a self-consistent dual vortex method and analyzing the saddle point
structures of the dual gauge fields carefully in the insulating side, we study
quantum phases, especially supersolid phases and phase transitions in an
extended boson Hubbard model at and slightly away from $ 1/3 $ ($ 2/3 $)
filling on a kagome lattice. We find phases and phase transitions in Kagome
lattice is dramatically different from those in bipartite and triangular
lattices in both Ising and Easy-plane limit. Slightly away from $ f=1/3 (2/3)
$, there is no supersolid in the Ising limit, but there are always supersolids
in the Easy-plane limit where we find a stripe solid and a new type of
supersolid which has charge density wave-valence bond-superfluid order and also
analyze their corresponding stability conditions. The results achieved resolve
some outstanding puzzles observed in recent QMC in a kagome lattice.
Implications on QMC simulations with both nearest neighbor and next nearest
neighbor interactions are given.
\\ ( , 23kb)

Date: Tue, 22 Apr 2008 12:25:47 GMT (152kb)

Title: Time reversal of Bose-Einstein condensates
Authors: J. Martin, B. Georgeot and D. L. Shepelyansky
Categories: cond-mat.stat-mech
Comments: 4 pages, 5 figures, research done at
   Using Gross-Pitaevskii equation, we study the time reversibility of
Bose-Einstein condensates (BEC) in kicked optical lattices, showing that inside
the regime of quantum chaos the dynamics can be inverted from explosion to
collapse. The accuracy of time reversal decreases with the increase of atom
interactions inside BEC, until it is completely lost. Surprisingly, quantum
chaos helps to restore time reversibility. These predictions can be tested with
existing experimental setups.
\\ ( , 152kb)

Date: Tue, 22 Apr 2008 14:24:13 GMT (304kb)

Title: Dynamics of saturated Bragg diffraction in a stored light grating in
   cold atoms
Authors: D. Moretti, N. Gonzalez, D. Felinto, and J. W. R. Tabosa
Categories: quant-ph
Comments: Submitted to Phys. Rev. A
   We report on a detailed investigation of the dynamics and the saturation of a
light grating stored in a sample of cold cesium atoms. We employ Bragg
diffraction to retrieve the stored optical information impressed into the
atomic coherence by the incident light fields. The diffracted efficiency is
studied as a function of the intensities of both writing and reading laser
beams. A theoretical model is developed to predict the temporal pulse shape of
the retrieved signal and compares reasonably well with the observed results.
\\ ( , 304kb)

Date: Tue, 22 Apr 2008 21:05:48 GMT (45kb,D)

Title: Josephson physics mediated by the Mott insulating phase
Authors: Smitha Vishveshwara and Courtney Lannert
Categories: cond-mat.mes-hall cond-mat.dis-nn
Comments: 4 pages, 1 figure
   We investigate the static and dynamic properties of bosonic lattice systems
in which condensed and Mott insulating phases co-exist due to the presence of a
spatially-varying potential. We formulate a description of these inhomogeneous
systems and calculate the bulk energy at and near equilibrium. We derive the
explicit form of the Josephson coupling between disjoint superfluid regions
separated by Mott insulating regions. We obtain detailed estimates for the
experimentally-realized case of alternating superfluid and Mott insulating
spherical shells in a radially symmetric parabolically-confined cold atom
\\ ( , 45kb)

Date: Wed, 23 Apr 2008 10:01:47 GMT (11kb)

Title: Entanglement production with Bose atoms in optical lattices
Authors: V.I. Yukalov and E.P. Yukalova
Categories: cond-mat.other
Comments: Latex file, 14 pages
Journal-ref: J. Phys. Conf. Ser. 104 (2008) 012003
   A method of entanglement production is suggested, based on the resonant
generation of topological modes in systems with Bose-Einstein condensates
trapped in optical or magnetic lattices. The method makes it possible to
regulate the strength of entanglement production as well as to govern its time
variation. This method can serve as a practical tool for quantum information
processing and quantum computing.
\\ ( , 11kb)

Date: Wed, 23 Apr 2008 12:57:02 GMT (261kb)

Title: Quantum phase transition and critical fluctuations of an attractive Bose
   gas in a double well potential
Authors: P. Zi\'n, J. Chwede\'nczuk, B. Ole\'s, K. Sacha and M. Trippenbach
Categories: cond-mat.other
   We consider a Bose gas with an attractive interaction in a symmetric double
well potential. In the Hartree approximation, the ground state solution
spontaneously breaks the symmetry of the trapping potential above certain value
of the interaction strength. We demonstrate how the Landau-Ginzburg scheme of
the second order phase transition emerges from the quantum model and show its
link to the spontaneous symmetry breaking mentioned above. We identify the
order parameter, the critical point and analyze quantum fluctuations around it.
\\ ( , 261kb)

Date: Wed, 23 Apr 2008 14:38:12 GMT (91kb,D)

Title: Coherent backscattering of Bose-Einstein condensates in two-dimensional
   disorder potentials
Authors: Michael Hartung, Thomas Wellens, Cord A. Mueller, Klaus Richter, Peter
Categories: cond-mat.other cond-mat.dis-nn
Comments: 4 pages, 4 figures
   We study quantum transport of an interacting Bose-Einstein condensate in a
two-dimensional disorder potential. In the limit of vanishing atom-atom
interaction, a sharp cone in the angle-resolved density of the scattered matter
wave is observed, arising from constructive interference between amplitudes
propagating along reversed scattering paths. Weak interaction transforms this
coherent backscattering peak into a pronounced dip, indicating destructive
instead of constructive interference. We reproduce this result, obtained from
the numerical integration of the Gross-Pitaevskii equation, by a diagrammatic
theory of weak localization in presence of a nonlinearity.
\\ ( , 91kb)

arXiv:0804.2919 (*cross-listing*)
Date: Thu, 17 Apr 2008 23:25:47 GMT (13kb)

Title: Low energy density correlation function of the degenerate unitary Fermi
   gas from epsilon expansion
Authors: Andrei Kryjevski
Categories: nucl-th cond-mat.other
Comments: 10 pages, 1 figure
   Using $\epsilon$ expansion proposed in \cite{Nishida:2006br} we calculate
density correlation function of the degenerate Fermi gas at infinite scattering
length to next-to-leading order in $\epsilon$ for excitation energies below
quasi particle threshold. An expression for the low energy dynamic structure
function is derived.
\\ ( , 13kb)

arXiv:0804.3501 (*cross-listing*)
Date: Tue, 22 Apr 2008 14:46:19 GMT (793kb)

Title: Lattice simulations for few- and many-body systems
Authors: Dean Lee (North Carolina State University)
Categories: nucl-th cond-mat.other hep-lat
Comments: 64 pages, 21 figures
   We review the recent literature on lattice simulations for few- and many-body
systems. We focus on methods and results that combine the framework of
effective field theory with computational lattice methods. Lattice effective
field theory is discussed for cold atoms as well as low-energy nucleons with
and without pions. A number of different lattice formulations and computational
algorithms are considered, and an effort is made to show common themes in
studies of cold atoms and low-energy nuclear physics as well as common themes
in work by different collaborations.
\\ ( , 793kb)

Date: Thu, 24 Apr 2008 05:44:03 GMT (352kb)

Title: Rosen-Zener interferometry with Ultracold Atoms
Authors: Li-Bin Fu, Di-Fa Ye, Chaohong Lee, Weiping Zhang, and Jie Liu
Categories: cond-mat.mes-hall
Comments: 4 pages, 5 figures
   We propose a time-domain "interferometer" based on ultracold Bose atoms
loaded on a double well potential. By the adiabatic Rosen-Zener process, the
barrier between two wells is ramped down slowly, held for a while, then ramped
back. Starting with a coherent state of double well system, the final
occupations on one well show interesting interference fringes in the
time-domain. The fringe pattern is sensitive to the initial state and can be
controlled by the hold time. This interferometric scheme provides new
possibilities for precision measurements with ultracold atoms. The underlying
mechanism is revealed and possible applications are discussed.
\\ ( , 352kb)

Date: Thu, 24 Apr 2008 18:02:01 GMT (284kb)

Title: Incommensurate superfluidity of bosons in a double-well optical lattice
Authors: Vladimir M. Stojanovic, Congjun Wu, W. Vincent Liu, S. Das Sarma
Categories: cond-mat.other
Comments: 4 pages, 5 figures
   We study cold bosons in the first excited Bloch band of a double-well optical
lattice, recently realized at NIST. By calculating parameters of the
Bose-Hubbard model from a realistic nonseparable lattice potential, we find
that in the most favorable cases the boson lifetime in the first excited band
can be several orders of magnitude longer than the typical nearest-neighbor
tunnelling timescales, in contrast to that of a simple single-well lattice. In
addition, for sufficiently small lattice depths the excited band has minima at
nonzero momenta incommensurate with the lattice period, which opens a
possibility to realize an exotic superfluid state that spontaneously breaks the
time-reversal, rotational, and translational symmetries. We discuss possible
experimental signatures of this novel state.
\\ ( , 284kb)

Date: Thu, 24 Apr 2008 19:27:18 GMT (68kb)

Title: Renormalization group flow for fermionic superfluids at zero temperature
Authors: P. Strack, R. Gersch, W. Metzner
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 14 pages, 12 Figures, submitted to Phys. Rev. B
   We present a comprehensive analysis of quantum fluctuation effects in the
superfluid ground state of an attractively interacting Fermi system, employing
the attractive Hubbard model as a prototype. The superfluid order parameter,
and fluctuations thereof, are implemented by a bosonic Hubbard-Stratonovich
field, which splits into two components corresponding to longitudinal and
transverse (Goldstone) fluctuations. Physical properties of the system are
computed from a set of approximate flow equations obtained by truncating the
exact functional renormalization group flow of the coupled fermion-boson
action. The equations capture the influence of fluctuations on non-universal
quantities such as the fermionic gap, as well as the universal infrared
asymptotics present in every fermionic superfluid. We solve the flow equations
numerically in two dimensions and compute the asymptotic behavior analytically
in two and three dimensions. The fermionic gap \Delta is reduced significantly
compared to the mean-field gap, and the bosonic order parameter \alpha, which
is equivalent to \Delta in mean-field theory, is suppressed to values below
\Delta by fluctuations. The fermion-boson vertex is only slightly renormalized.
In the infrared regime, transverse order parameter fluctuations associated with
the Goldstone mode lead to a strong renormalization of longitudinal
fluctuations: the longitudinal mass and the bosonic self-interaction vanish
linearly as a function of the scale in two dimensions, and logarithmically in
three dimensions, in agreement with the exact behavior of an interacting Bose
\\ ( , 68kb)

Date: Thu, 24 Apr 2008 17:54:53 GMT (13kb)

Title: Matrix product operator representations
Authors: V. Murg, J.I. Cirac, B. Pirvu, F. Verstraete
Categories: quant-ph
Comments: comment welcome
   We show how to construct relevant families of matrix product operators in one
and higher dimensions. Those form the building blocks for the numerical
simulation methods based on matrix product states and projected entangled pair
states. In particular, we construct translational invariant matrix product
operators suitable for time evolution, and show how such descriptions are
possible for Hamiltonians with long-range interactions. We illustrate how those
tools can be exploited for constructing new algorithms for simulating quantum
spin systems.
\\ ( , 13kb)

Date: Thu, 24 Apr 2008 18:33:06 GMT (217kb)

Title: Narrow-Band Biphoton Generation near Atomic Resonance
Authors: Shengwang Du, Jianming Wen, and Morton H. Rubin
Categories: quant-ph
Comments: 12 pages, 4 figures, a review on narrow-band paired photons generated
   from an atomic-gase medium near resonance, submitted to JOSA B (2008)
   Generating nonclassical light offers a benchmark tool for the fundamental
research and potential applications in quantum optics. Conventionally, it has
become a standard technique to produce the nonclassical light through the
nonlinear optical processes occurring in nonlinear crystals. In this review we
describe using cold atomic-gas media to generate such nonclassical light,
especially focusing on narrow-band biphoton generation. Compared with the
standard procedure, the new biphoton source has such properties as long
coherence time, long coherence length, high spectral brightness, and high
conversion efficiency. In this paper we concentrate on the theoretical aspect
of the entangled two-photon state produced from the four-wave mixing in a
multilevel atomic ensemble. We show that both linear and nonlinear optical
responses to the generated fields play an important role in determining the
biphoton waveform and, consequently on the two-photon temporal correlation.
There are two characteristic regimes determined by whether the linear or
nonlinear coherence time is dominant. In addition, our model provides a clear
physical picture that brings insight into understanding biphoton optics with
this new source. We apply our model to recent work on generating narrow-band
(and even subnatural linewidth) paired photons using the technique of
electromagnetically induced transparency and slow-light effect in cold atoms,
and find good agreements with experimental results.
\\ ( , 217kb)

and just because they caught my eye:

Date: Fri, 18 Apr 2008 15:52:31 GMT (106kb)

Title: Gravitation as a Casimir interaction
Authors: Bo E. Sernelius
Categories: quant-ph
   Gravitation is considered to be one of the four fundamental interactions in
nature. However, one has so far failed to observe the graviton, the quantum
particle that is believed to transmit the gravitational force at a distance -
the analogue to the photon in electromagnetism. Maybe it is now time to
re-evaluate the status of the gravitation as a fundamental interaction. Here,
we propose a completely new interpretation of gravitation. In this description
the gravitational force is no longer a fundamental force. It is an induced
force, a dispersion force, and the analogue to the Casimir force in
electromagnetism. The fundamental force is in our description a force between
particles with a parabolic interaction potential. In our model the nucleons are
made up from these particles. We find the retarded dispersion force between
these composite particles has the correct distance dependence, 1/r. If this
interpretation is correct it has a broad range of implications. Our view on the
fundamental concept mass is altered; our view on the expansion of the Universe
may change.
\\ ( , 106kb)

Date: Fri, 18 Apr 2008 17:59:35 GMT (217kb)

Title: Operator Imprecision and Scaling of Shor's Algorithm
Authors: C. Ray Hill and George F. Viamontes
Categories: quant-ph
Comments: 15 pages
   Shor's algorithm (SA) is a quantum algorithm for factoring integers. Since SA
has polynomial complexity while the best classical factoring algorithms are
sub-exponential, SA is cited as evidence that quantum computers are more
powerful than classical computers. SA is critically dependent on the Quantum
Fourier Transform (QFT) and it is known that the QFT is sensitive to errors in
the quantum state input to it. In this paper, we show that the polynomial
scaling of SA is destroyed by input errors to the QFT part of the algorithm. We
also show that Quantum Error Correcting Codes (QECC) are not capable of
suppressing errors due to operator imprecision and that propagation of operator
precision errors is sufficient to severely degrade the effectiveness of SA.
Additionally we show that operator imprecision in the error correction circuit
for the Calderbank-Shor-Steane QECC is mathematically equivalent to decoherence
on every physical qubit in a register. We conclude that, because of the effect
of operator precision errors, it is likely that physically realizable quantum
computers will be capable of factoring integers no more efficiently than
classical computers.
\\ ( , 217kb)

The replacements:

replaced with revised version Fri, 18 Apr 2008 16:52:55 GMT (162kb,D)

Title: Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in
   Two-Component Atomic Gases
Authors: Artur Widera, Stefan Trotzky, Patrick Cheinet, Simon F\"olling,
   Fabrice Gerbier, Immanuel Bloch, Vladimir Gritsev, Mikhail D. Lukin and
   Eugene Demler
Categories: cond-mat.other
Comments: 4 pages, 3 figures Updated version, minor changes
Journal-ref: Phys. Rev. Lett. 100, 140401 (2008)
DOI: 10.1103/PhysRevLett.100.140401
\\ ( , 162kb)
replaced with revised version Fri, 18 Apr 2008 11:38:53 GMT (33kb)

Title: Fast rotating condensates in an asymmetric harmonic trap
Authors: Amandine Aftalion (LJLL), Xavier Blanc (LJLL), Nicolas Lerner (IMJ)
Categories: cond-mat.other
Comments: 4 pages, 2 figures
Proxy: ccsd hal-00270540
\\ ( , 33kb)
replaced with revised version Fri, 18 Apr 2008 17:59:21 GMT (564kb,D)

Title: Mott-Insulator Transition for Ultracold Fermions in Two-Dimensional
   Optical Lattices
Authors: N. Goldman
Categories: cond-mat.mes-hall
Comments: 7 pages, 7 figures, to appear in Physical Review A
\\ ( , 564kb)
replaced with revised version Wed, 16 Apr 2008 01:06:17 GMT (49kb)

Title: Feshbach resonances in ultracold ^{6,7}Li + ^{23}Na atomic mixtures
Authors: Marko Gacesa, Philippe Pellegrini, and Robin C\^ot\'e
Categories: physics.atom-ph
Comments: 4 pages, 2 figures
\\ ( , 49kb)
replaced with revised version Mon, 21 Apr 2008 17:30:26 GMT (315kb)

Title: Interaction induced trapping and pulsed emission of a magnetically
   insensitive Bose-Einstein Condensate
Authors: Stephan Middelkamp, Igor Lesanovsky, Peter Schmelcher
Categories: cond-mat.other
Comments: 4 pages, 4 figures
\\ ( , 315kb)
replaced with revised version Sat, 19 Apr 2008 17:16:54 GMT (301kb)

Title: Trapped Rydberg Ions: From Spin Chains to Fast Quantum Gates
Authors: M. Mueller, L.-M. Liang, I. Lesanovsky and P. Zoller
Categories: quant-ph physics.atom-ph
Comments: 26 pages, 9 figures
\\ ( , 301kb)
replaced with revised version Tue, 22 Apr 2008 19:10:16 GMT (123kb,D)

Title: Final-state effects in the radio frequency spectrum of strongly
   interacting fermions
Authors: Sourish Basu, Erich J. Mueller
Categories: cond-mat.str-el cond-mat.other
Comments: 4 pages, 4 figures
\\ ( , 123kb)
replaced with revised version Tue, 22 Apr 2008 09:20:31 GMT (317kb)

Title: Noise correlations of the ultra-cold Fermi gas in an optical lattice
Authors: T. Paananen, T. K. Koponen, P. T\"orm\"a, and J. -P. Martikainen
Categories: cond-mat.other
Comments: 25 pages, 11 figures. Some figures are updated and text has been
\\ ( , 317kb)
replaced with revised version Tue, 22 Apr 2008 12:35:20 GMT (372kb)

Title: Mean-field dynamics of a Bose Josephson junction in an optical cavity
Authors: J. M. Zhang, W. M. Liu, and D. L. Zhou
Categories: quant-ph cond-mat.stat-mech
Comments: revised according to the comments of the referee
\\ ( , 372kb)
replaced with revised version Tue, 22 Apr 2008 13:49:48 GMT (60kb)

Title: Quantum Interface for Nanomechanics and Atomic Ensembles
Authors: K. Hammerer, M. Aspelmeyer, E.S. Polzik, P. Zoller
Categories: quant-ph
Comments: 4 pages, 1 figure; references added, shortened text, corrected for
\\ ( , 60kb)
replaced with revised version Wed, 23 Apr 2008 08:47:21 GMT (13kb)

Title: The Josephson relation for the superfluid density in the BCS-BEC
Authors: Edward Taylor
Categories: cond-mat.other
Comments: Published version
Journal-ref: Phys. Rev. B 77 144521 (2008)
\\ ( , 13kb)
replaced with revised version Wed, 23 Apr 2008 00:36:30 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, Phys. Rev. A 77, 043624 (2008)
\\ ( , 287kb)
replaced with revised version Tue, 22 Apr 2008 23:11:12 GMT (226kb)

Title: Observation of quantum-measurement backaction with an ultracold atomic
Authors: Kater W. Murch, Kevin L. Moore, Subhadeep Gupta, and Dan M.
Categories: quant-ph
Comments: Article and supplementary information. Version submitted to Nature
\\ ( , 226kb)
replaced with revised version Wed, 23 Apr 2008 02:00:16 GMT (566kb)

Title: Lateral Effects in Fermion Antibunching
Authors: K. Yuasa, P. Facchi, H. Nakazato, I. Ohba, S. Pascazio, S. Tasaki
Categories: quant-ph
Comments: 22 pages, 4 figures
Journal-ref: Phys. Rev. A 77 (2008) 043623
DOI: 10.1103/PhysRevA.77.043623
\\ ( , 566kb)
replaced with revised version Wed, 23 Apr 2008 04:54:52 GMT (53kb)

Title: Hybrid phase-space simulation method for interacting Bose fields
Authors: Scott E. Hoffmann, Joel F. Corney and Peter D. Drummond
Categories: quant-ph
Comments: 13 pages; 6 figures; references added; figures corrected
\\ ( , 53kb)
replaced with revised version Wed, 23 Apr 2008 09:30:53 GMT (962kb,D)

Title: Trapping molecules on a chip in traveling potential wells
Authors: Samuel A. Meek, Hendrick L. Bethlem, Horst Conrad, Gerard Meijer
Categories: physics.atom-ph
Comments: 4 pages, 3 figures
Journal-ref: Phys. Rev. Lett. 100, 153003 (2008)
DOI: 10.1103/PhysRevLett.100.153003
\\ ( , 962kb)
replaced with revised version Thu, 24 Apr 2008 06:47:30 GMT (427kb)

Title: Trionic phase of ultracold fermions in an optical lattice: A variational
Authors: Akos Rapp, Walter Hofstetter, and Gergely Zarand
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 14 PRB pages, 8 figures
Journal-ref: Phys. Rev. B 77, 144520 (2008)
DOI: 10.1103/PhysRevB.77.144520
\\ ( , 427kb)
replaced with revised version Thu, 24 Apr 2008 10:33:39 GMT (339kb)

Title: Simulation of time evolution with the MERA
Authors: Matteo Rizzi, Simone Montangero, Guifre' Vidal
Categories: quant-ph cond-mat.other
Comments: final version with data improvement (precision and size), 4.1 pages,
   4 figures + extra on XY
\\ ( , 339kb)

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 May 08 2008 - 11:51:22 EST

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