Matt's arXiv selection: week ending 21 March 2008.

From: Matthew Davis <>
Date: Thu, 03 Apr 2008 08:19:18 +1000

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

Hi all,

There are a massive 42 preprints and 15 replacements this week. You guys
definitely work too hard...

Date: Fri, 14 Mar 2008 04:55:45 GMT (31kb)

Title: Defect production in non-linear quench across a quantum critical point
Authors: Diptiman Sen, K. Sengupta, and Shreyoshi Mondal
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 4pg. 2 Figs., v1
   We show that the defect density $n$, for a slow non-linear power-law quench
with a rate $\tau^{-1}$ and an exponent $\alpha>0$, which takes the system
through a critical point characterized by correlation length and dynamical
critical exponents $\nu$ and $z$, scales as $n \sim \tau^{-\alpha \nu d/
(\alpha z\nu+1)}$ [$n \sim (\alpha g^{(\alpha-1)/\alpha}/\tau)^{\nu
d/(z\nu+1)}$], if the quench takes the system across the critical point at time
$t=0$ [$t=t_0 \ne 0$], where $g$ is a non-universal constant and $d$ is the
system dimension. These scaling laws constitute the first theoretical results
for defect production in non-linear quenches across quantum critical points and
reproduce their well-known counterpart for linear quench ($\alpha=1$) as a
special case. We supplement our results with numerical studies of well-known
models and suggest experiments to test our theory.
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Date: Fri, 14 Mar 2008 05:12:23 GMT (52kb)

Title: BCS-BEC crossover and effects of density fluctuations in a two-component
   Fermi gas loaded on an optical lattice
Authors: H. Tamaki, Y. Ohashi, K. Miyake
Categories: cond-mat.mtrl-sci
   We investigate the superfluid phase transition in a gas of Fermi atoms loaded
on a three-dimensional optical lattice. When the lattice potential is strong,
this system can be well described by an attractive Hubbard model. In this
model, we calculate the superfluid phase transition temperature Tc, including
both superfluid and (spin and charge) density fluctuations within the
self-consistent t-matrix theory and fluctuation exchange approximation,
respectively. Since we treat these fluctuations in a consistent manner, our
theory satisfies the required particle-hole symmetry over the entire BCS-BEC
crossover region. We show that charge density fluctuations compete against
superfluid fluctuations near the half-filling, leading to the suppression of
Tc. As a result, the maximum Tc is obtained away the half-filling. Since the
strong density fluctuations originate from the nesting property of the Fermi
surface at the half filling (which is absent in a uniform gas with no lattice
potential), our results would be useful in considering lattice effects on
strong-coupling superfluidity.
\\ ( , 52kb)
Date: Fri, 14 Mar 2008 13:25:13 GMT (323kb)

Title: Interaction induced trapping of a magnetically insensitive Bose-Einstein
Authors: Stephan Middelkamp, Igor Lesanovsky, Peter Schmelcher
Categories: cond-mat.other
Comments: 10 pages, 4 figures
   We demonstrate that atoms in magnetically insensitive hyperfine states (m=0)
can be trapped efficiently by a Bose-Einstein Condensate of the same atomic
species occupying a different hyperfine state. The latter is trapped
magnetically. Hyperfine state changing collisions, and therefore loss of the
trapped (m=0) atoms, are shown to be strongly inhibited in case of a low
density of the confined atomic cloud. We monitor the transition from a 'soft'
to a 'hard' effective potential by studying the backaction of the trapped (m=0)
atoms onto the condensate which provides their confinement. The controlled
release of the trapped atoms by shaping the condensate's wavefunction is
\\ ( , 323kb)
Date: Fri, 14 Mar 2008 15:45:08 GMT (148kb)

Title: Comment on "Splitting Times of Doubly Quantized Vortices in Dilute
   Bose-Einstein Condensates"
Authors: K. Gawryluk, T. Karpiuk, M. Brewczyk, and K. Rzazewski
Categories: cond-mat.other
Comments: 1 page, 1 figure
   In their recent Letter [1], Huhtamaki et al. theoretically investigated the
splitting of a topologically imprinted doubly charged vortex in to two singly
charged vortices as occurring in a dilute atomic Bose-Einstein conden sate.
They compare the results of simulation with recent experiment [2] and show that
the combination of gravitational sag and the time dependence of the trapping
potential alone are enough to explain the observed splitting times. In
particular, the numerically obtained dependence of the decay time on the peak
condensate density fits well the experimental data. Based on this agreement the
authors of Ref. [1] claim that, contrary to previous theoretical results [3],
the thermal excitations play no role in the experiment. We are going to show in
this Comment that there is no conflict between explanations in Ref. [1] and
[3]. In fact, a number of thermal (uncondensed) atoms appears in the system
while disturbing the gas. They continue to appear afterwords during the decay
of the vortex (i.e., when the separation between two cores of singly quantized
vortices is slowly increasing). The overall number of uncondensed atoms remains
approximately on the level of 20%, which is already at the edge of experimental
detection capabilities. However, the uncondensed atoms do not form the broad
cloud allowing the identification by fitting to a bimodal distribution - they
are rather located in the core of the vortex and therefore are harder to
   [1] J.A.M. Huhtam\"aki et al., Phys. Rev. Lett. 97, 110406 (2006) [2] Y. Shin
et al., Phys. Rev. Lett. 93, 160406 (2004) [3] K. Gawryluk, M. Brewczyk, and K.
Rzazewski, J. Phys. B 39, L225 (2006)
\\ ( , 148kb)
Date: Fri, 14 Mar 2008 16:54:37 GMT (25kb)

Title: The Cooper pair from radio-frequency excitations in ultracold gases
Authors: J. Dukelsky and G. Ortiz
Categories: cond-mat.other
Comments: Three pages, 1 figure
   We discuss the concept of Cooper pair in the context of recent experimental
studies of radio-frequency excitations in ultracold atomic gases. We argue that
the threshold energy determines the size of the Cooper pair emergent from the
exact solution of the reduced BCS problem, and elaborate on the physical
distinction between bosonic and fermionic Cooper pairs.
\\ ( , 25kb)
Date: Fri, 14 Mar 2008 07:38:49 GMT (356kb,D)

Title: Delay of Squeezing and Entanglement using Electromagnetically Induced
   Transparency in a Vapour Cell
Authors: G. H\'etet, B. C. Buchler, O. Gl\"ockl, M. T. L. Hsu, A. M. Akulshin,
   H. -A. Bachor, and P. K. Lam
Categories: quant-ph
Comments: 8 pages, 5 figures
   We demonstrate experimentally the delay of squeezed light and entanglement
using Electromagnetically Induced Transparency (EIT) in a rubidium vapour cell.
We perform quadrature amplitude measurements of the probe field and find no
appreciable excess noise from the EIT process. From an input squeezing of 3.1
dB at low sideband frequencies, we observed the survival of 2 dB of squeezing
at the EIT output. By splitting the squeezed light on a beam-splitter, we
generated biased entanglement between two beams. We transmit one of the
entangled beams through the EIT cell and correlate the quantum statistics of
this beam with its entangled counterpart. We experimentally observed a 2 $\mu$s
delay of the biased entanglement and obtained a preserved degree of
wavefunction inseparability of 0.71, below the unity value for separable
\\ ( , 356kb)
Date: Fri, 14 Mar 2008 13:08:08 GMT (703kb)

Title: Two-dimensional array of microtraps with atomic shift register on a chip
Authors: S. Whitlock, R. Gerritsma, T. Fernholz, and R. J. C. Spreeuw
Categories: physics.atom-ph
Comments: 6 pages, 4 figures
   Arrays of trapped atoms are the ideal starting point for developing registers
comprising large numbers of physical qubits for processing quantum information.
One very promising approach involves neutral atom traps produced on
microfabricated devices known as atom chips, as almost arbitrary trap
configurations can be realised in a robust and compact package. Until now,
however, atom chip experiments have focused on small systems incorporating
single or only a few individual traps. In this letter we report experiments on
a vast two-dimensional array of trapped ultracold atom clouds prepared using a
simple magnetic-film atom chip. We are able to load atoms into hundreds of
tightly confining and optically resolved array sites. We then cool the
individual atom clouds in parallel to the critical temperature required for
quantum degeneracy. Finally, we shuttle atoms across the film surface utilising
the atom chip as an atomic shift register.
\\ ( , 703kb)
Date: Fri, 14 Mar 2008 14:14:48 GMT (48kb)

Title: Simulations of Sisyphus cooling including multiple excited states
Authors: F. Svensson, S. Jonsell, C. M. Dion
Categories: physics.atom-ph
Comments: 7 pages, 6 figures
   We extend the theory for laser cooling in a near-resonant optical lattice to
include multiple excited hyperfine states. Simulations are performed treating
the external degrees of freedom of the atom, i.e., position and momentum,
classically, while the internal atomic states are treated quantum mechanically,
allowing for arbitrary superpositions. Whereas theoretical treatments including
only a single excited hyperfine state predict that the temperature should be a
function of lattice depth only, except close to resonance, experiments have
shown that the minimum temperature achieved depends also on the detuning from
resonance of the lattice light. Our results resolve this discrepancy.
\\ ( , 48kb)

Date: Mon, 17 Mar 2008 17:34:30 GMT (600kb)

Title: Phase Cat States with Bose-Einstein Condensates
Authors: F. Piazza, L. Pezze', and A. Smerzi
Categories: cond-mat.other
   We discuss the creation of quantum superposition states with distinct phases
(phase cat states) with a Bose-Einstein condensate trapped in a periodic
potential. The signature of the cat is con- tained in the phase distribution of
the interference patterns. Moreover, in the double well case, this distribution
shows a dramatic dependence on the parity of the total number of atoms. We
finally show that, for single well occupations up to a few hundred atoms, the
phase cats can be robust enough against decoherence to be experimentally
observable within current technology.
\\ ( , 600kb)
Date: Sat, 15 Mar 2008 12:48:21 GMT (23kb)

Title: Superfluid to insulator phase transition in a unitary Fermi gas
Authors: Nir Barnea
Categories: cond-mat.stat-mech
Comments: 4 pages,4 figures
   We study the evolution of the energy gap in a unitary Fermi gas as a function
of temperature. To this end we approximate the Fermi gas by the Hubbard lattice
Hamiltonian and solve using the dynamical mean-field approximation. We have
found that below the critical temperature, Tc, the system is a superfluid and
the energy gap is decreasing monotonously. For temperatures above Tc the system
is an insulator and the corresponding energy gap is monotonously increasing.
\\ ( , 23kb)
Date: Sat, 15 Mar 2008 17:58:35 GMT (43kb)

Title: Effects of disorder on atomic density waves and spin-singlet dimers in
   one-dimensional optical lattices
Authors: Gao Xianlong
Categories: cond-mat.str-el
Comments: 16 pages, submitted
   Using Bethe-ansatz density-functional theory, we study the one-dimensional
Hubbard model of confined attractively interacting fermions in the presence of
a uniformly distributed disorder. The strongly-correlated Luther-Emery nature
of the attractive one-dimensional Hubbard model is fully taken into account as
the reference system in the density-functional theory. The effects of the
disorder are investigated on atomic-density waves in the weak-to-intermediate
attractive interaction and on spin-singlet dimers of doubly occupied sites in
the strongly attractive regime. It is found that the atomic density waves are
sensitive to the disorder and the spin-singlet dimers of doubly occupied sites
are quite unstable against the disorder. We show also that very weak disorder
could smear the singularities in the stiffness, thus suppress the spin-singlet
\\ ( , 43kb)
Date: Sun, 16 Mar 2008 08:07:24 GMT (158kb)

Title: Effects of Zero Mode and Thin Spectrum on the Life Time of Atomic Bose
   Einstein Condensates
Authors: Turan Birol, \"Ozg\"ur E. M\"ustecapl{\i}o\u{g}lu
Categories: cond-mat.other
Comments: 8 pages, 9 figures, Proceeding of 14th Central European Workshop on
   Quantum Optics To be published in European Physical Journal Special Topics
   Reviewing the ideas developed in, the ground state life time of a finite size
atomic Bose Einstein condensate is studied for coherent, squeezed coherent and
thermal coherent ground states. Ground state evolution of coherent and squeezed
coherent states in a double well potential is studied. Effects of thin spectrum
on Bose-Einstein condensates is discussed and quasiparticle excitation
lifetimes are calculated. It is shown that the effect of the states we use on
the free energy vanishes in the thermodynamic limit. Possible extension to a
double well potential and effect of a second broken symmetry is also discussed.
\\ ( , 158kb)
Date: Sun, 16 Mar 2008 15:08:30 GMT (866kb)

Title: Weakly non-ergodic Statistical Physics
Authors: Adi Rebenshtok, Eli Barkai
Categories: cond-mat.stat-mech
   We find a general formula for the distribution of time averaged observables
for weakly non-ergodic systems. Such type of ergodicity breaking is known to
describe certain systems which exhibit anomalous fluctuations, e.g. blinking
quantum dots and the sub-diffusive continuous time random walk model. When the
fluctuations become normal we recover usual ergodic statistical mechanics.
Examples of a particle undergoing fractional dynamics in a binding force field
are worked out in detail. We briefly discuss possible physical applications in
single particle experiments.
\\ ( , 866kb)
Date: Mon, 17 Mar 2008 17:53:00 GMT (122kb)

Title: Joule expansion of a pure many-body state
Authors: S. Camalet
Categories: cond-mat.other
   We derive the Joule expansion of an isolated perfect gas from the principles
of quantum mechanics. Contrary to most studies of irreversible processes which
consider composite systems, the gas many-body Hilbert space cannot be
factorised into Hilbert spaces corresponding to interesting and ignored degrees
of freedom. Moreover, the expansion of the gas into the entire accessible
volume is obtained for pure states. Still, the number particle density is
characterised by a chemical potential and a temperature. We discuss the special
case of a boson gas below the Bose condensation temperature.
\\ ( , 122kb)
Date: Mon, 17 Mar 2008 13:23:12 GMT (755kb)

Title: d-wave collapse and explosion of a dipolar Bose-Einstein condensate
Authors: Thierry Lahaye, Jonas Metz, Bernd Froehlich, Tobias Koch, Maximilian
   Meister, Axel Griesmaier, Tilman Pfau, Hiroki Saito, Yuki Kawaguchi and
   Masahito Ueda
Categories: cond-mat.other
Comments: 4 pages, 4 figures, submitted to Nature Physics
   We report on the observation of the d-wave symmetry in the collapse of a
dipolar quantum fluid. More specifically, we experimentally investigate the
collapse dynamics of a dipolar condensate of Cr atoms when the s-wave
scattering length is reduced below the critical value for which the condensate
becomes unstable. A complex dynamics, involving an anisotropic, d-wave
symmetric explosion of the condensate, is observed on time scales significantly
shorter than the trap period. At the same time, the condensate atom number
decreases abruptly during the collapse. We compare our experimental results
with numerical simulations of the three-dimensional Gross-Pitaevskii equation
including the contact and dipolar interactions as well as three-body losses. An
excellent agreement between experiment and theory is obtained. The numerical
simulation indicates that the collapse is accompanied by the formation of two
vortex rings with opposite circulations. The d-wave character of the dipolar
interaction, directly observed here in the collapse dynamics, is expected to
enrich considerably the physics of quantum gases.
\\ ( , 755kb)
Date: Mon, 17 Mar 2008 17:18:48 GMT (56kb)

Title: BCS-BEC Crossover of a Quasi-two-dimensional Fermi Gas: the Significance
   of Dressed Molecules
Authors: Wei Zhang, G.-D. Lin, and L.-M. Duan
Categories: cond-mat.str-el cond-mat.supr-con
Comments: 5 pages, 3 figures
   We study the crossover of a quasi-two-dimensional Fermi gas trapped in the
radial plane from the Bardeen-Cooper-Schrieffer (BCS) regime to the
Bose-Einstein condensation (BEC) regime by crossing a wide Feshbach resonance.
Using an effective two-dimensional Hamiltonian with renormalized interaction
between atoms and dressed molecules, we calculate the zero temperature cloud
size and number density distribution and conclude that the results are
consistent with the picture of a BCS-BEC crossover. These results are in clear
contrast to the predictions of an effective two-dimensional Hamiltonian with
renormalized atom-atom interaction, where a constant cloud size and identical
density profile are expected for arbitrary detunings. This inconsistence
indicates that the inclusion of dressed molecules is essential to describe
quasi-two-dimensional Fermi systems, especially on the BEC side of the Feshbach
\\ ( , 56kb)
Date: Mon, 17 Mar 2008 17:48:12 GMT (69kb)

Title: Vortex dynamics in rotating counterflow and plane Couette and Poiseuille
   turbulence in superfluid Helium
Authors: David Jou, Michele Sciacca and Maria Stella Mongiovi'
Categories: cond-mat.other
Comments: 18 pages, 2 figures
   An equation previously proposed to describe the evolution of vortex line
density in rotating counterflow turbulent tangles in superfluid helium is
generalized to incorporate nonvanishing barycentric velocity and velocity
gradients. Our generalization is compared with an analogous approach proposed
by Lipniacki, and with experimental results by Swanson et al. in rotating
counterflow, and it is used to evaluate the vortex density in plane Couette and
Poiseuille flows of superfluid helium.
\\ ( , 69kb)
Date: Thu, 13 Mar 2008 08:09:07 GMT (608kb)

Title: Geometric phases and quantum phase transitions
Authors: Shi-Liang Zhu
Categories: quant-ph cond-mat.str-el
Comments: Invited review article for IJMPB; material covered till June 2007; 10
Journal-ref: International Journal of Modern Physics B 22, 561-581 (2008)
   Quantum phase transition is one of the main interests in the field of
condensed matter physics, while geometric phase is a fundamental concept and
has attracted considerable interest in the field of quantum mechanics. However,
no relevant relation was recognized before recent work. In this paper, we
present a review of the connection recently established between these two
interesting fields: investigations in the geometric phase of the many-body
systems have revealed so-called "criticality of geometric phase", in which
geometric phase associated with the many-body ground state exhibits
universality, or scaling behavior in the vicinity of the critical point. In
addition, we address the recent advances on the connection of some other
geometric quantities and quantum phase transitions. The closed relation
recently recognized between quantum phase transitions and some of geometric
quantities may open attractive avenues and fruitful dialog between different
scientific communities.
\\ ( , 608kb)
Date: Mon, 17 Mar 2008 11:48:40 GMT (403kb,D)

Title: Space-like Separation in a Bell Test assuming Gravitationally Induced
Authors: D. Salart, A. Baas, J.A.W. van Houwelingen, N. Gisin, and H. Zbinden
Categories: quant-ph
   We report on a Bell experiment with space-like separation assuming that the
measurement time is related to gravity-induced state reduction. Two energy-time
entangled photons are sent through optical fibers and directed into unbalanced
interferometers at two receiving stations separated by 18 km. At each station,
the detection of a photon triggers the displacement of a macroscopic mass. The
timing ensures space-like separation from the moment a photon enters its
interferometer until the mass has moved. 2-photon interference fringes with a
visibility of up to 90.5% are obtained, leading to a violation of Bell
\\ ( , 403kb)
Date: Mon, 17 Mar 2008 13:52:33 GMT (928kb,D)

Title: Low-energy excitations of a boson pair in a double-well trap
Authors: D.S. Murphy and J.F. McCann
Categories: quant-ph
Comments: 16 pages, 15 figures
   The states of a boson pair in a one-dimensional double-well potential are
investigated. Properties of the ground and lowest excited states of this system
are studied, including the two-particle wavefunction, momentum pair
distribution and entanglement. The effects of varying both the barrier height
and the effective interaction strength are investigated.
\\ ( , 928kb)
Date: Mon, 17 Mar 2008 20:41:19 GMT (547kb)

Title: Radio frequency spectroscopy of a strongly imbalanced Feshbach-resonant
   Fermi gas
Authors: Martin Veillette, Eun Gook Moon, Austen Lamacraft, Leo Radzihovsky,
   Subir Sachdev, and D.E. Sheehy
Categories: cond-mat.str-el cond-mat.supr-con
Comments: 10 pages, 5 figures
   A sufficiently large species imbalance (polarization) in a two-component
Feshbach resonant Fermi gas is known to drive the system into its normal state.
We show that the resulting strongly-interacting state is a conventional Fermi
liquid, that is, however, strongly renormalized by pairing fluctuations. Using
a controlled 1/N expansion, we calculate the properties of this state with a
particular emphasis on the atomic spectral function, the momentum distribution
functions displaying the Migdal discontinuity, and the radio frequency (RF)
spectrum. We discuss the latter in the light of the recent experiments of
Schunck et al. (cond-mat/0702066) on such a resonant Fermi gas, and show that
the observations are consistent with a conventional, but strongly renormalized
Fermi-liquid picture.
\\ ( , 547kb)
Date: Tue, 18 Mar 2008 02:18:28 GMT (908kb)

Title: Formation of Quantum Shock Waves by Merging and Splitting Bose-Einstein
Authors: J.J. Chang, P. Engels, M. A. Hoefer
Categories: cond-mat.other
Comments: 10 pages, 8 figures
   The processes of merging and splitting dilute-gas Bose-Einstein condensates
are studied in the nonadiabatic, high-density regime. Rich dynamics are found.
Depending on the experimental parameters, uniform soliton trains containing
more than ten solitons or the formation of a high-density bulge as well as
quantum (or dispersive) shock waves are observed experimentally within merged
BECs. Our numerical simulations indicate the formation of many vortex rings. In
the case of splitting a BEC, the transition from sound-wave formation to
dispersive shock-wave formation is studied by use of increasingly stronger
splitting barriers. These experiments realize prototypical dispersive shock
\\ ( , 908kb)
Date: Tue, 18 Mar 2008 07:43:55 GMT (422kb)

Title: Kelvin Waves in Bose-Einstein Condensates
Authors: T. P. Simula, T. Mizushima, and K. Machida
Categories: cond-mat.other
Comments: 4 pages, 4 figure
   We have theoretically investigated Kelvin waves of quantized vortex lines in
trapped Bose-Einstein condensates. Counter-rotating perturbation induces an
elliptical instability to the initially straight vortex line, driven by a
parametric resonance between a quadrupole surfon and a pair of kelvons of
opposite momenta. Subsequently Kelvin waves rapidly decay to longer wavelengths
emitting sound waves in the process. We present a modified Kelvin wave
dispersion relation for trapped superfluids and propose a simple method to
excite Kelvin waves of specific wave number.
\\ ( , 422kb)
Date: Tue, 18 Mar 2008 09:29:12 GMT (311kb)

Title: Magnetization profile and core level spectroscopy in a multiply
   quantized vortex of imbalanced Fermi superfluids
Authors: K. M. Suzuki, T. Mizushima, M. Ichioka, K. Machida
Categories: cond-mat.supr-con
Comments: 10 pages, 6 figures
   The core structure of multiply quantized vortices is theoretically
investigated in fermionic superfluid near Feshbach resonance. Under population
imbalance in two hyperfine spin states, the vortex core is filled in by the
``paramagnetic moment''. Here, we find the spatial oscillation of the
magnetization inside the core sensitively due to the topological structure of
the pairing field, in the range from the weak coupling regime to the unitary
limit. This magnetization inside the giant core reveals the winding number of
the vortex and directly results from the low-lying quasiparticle states bound
inside the core. It is therefore proposed that the density profile experiment
using phase contrast imaging can provide the spectroscopy of novel core level
structures in giant vortices. To help the understanding on these outcomes, we
also derive the analytic solution for the low-lying quasiparticle states inside
the core of a multiply quantized vortex.
\\ ( , 311kb)
Date: Tue, 18 Mar 2008 15:58:59 GMT (488kb)

Title: Theory of cavity-assisted microwave cooling of polar molecules
Authors: Margareta Wallquist, Peter Rabl, Mikhail D. Lukin and Peter Zoller
Categories: quant-ph
   We analyze cavity-assisted cooling schemes for polar molecules in the
microwave domain, where molecules are excited on a rotational transition and
energy is dissipated via strong interactions with a lossy stripline cavity, as
recently proposed by A. Andre et al., Nature Physics 2, 636 (2006). We identify
the dominant cooling and heating mechanisms in this setup and study cooling
rates and final temperatures in various parameter regimes. In particular we
analyze the effects of a finite environment temperature on the cooling
efficiency, and find minimal temperature and optimized cooling rate in the
strong drive regime. Further we discuss the trade-off between efficiency of
cavity cooling and robustness with respect to ubiquitous imperfections in a
realistic experimental setup, such as anharmonicity of the trapping potential.
\\ ( , 488kb)
Date: Tue, 18 Mar 2008 20:04:11 GMT (614kb)

Title: Meta-nematic, smectic and crystalline phases of dipolar fermions in an
   optical lattice
Authors: J. Quintanilla, S. T. Carr, J. J. Betouras
Categories: cond-mat.other cond-mat.str-el
Comments: 10 pages, 5 figures
   Strongly correlated quantum matter (from high-temperature superconductors,
through oxides and heavy fermions to quantum Hall devices) remains an
outstanding scientific challenge. In it, electron itineracy survives in spite
of strong interactions. A general framework was proposed for its understanding
in [Kivelson, Fradkin and Emery, Nature 393, 550-553 (1998)]. It rests on
liquid crystalline phases intervening between the Fermi gas and the Wigner
crystal or Mott insulator as the strength of correlations increases. In this
work we propose an alternative realisation of the relevant physics in an
ultra-cold atomic gas. It exploits optical lattices and dipolar interactions to
realise a particularly simple model which can be tuned systematically. We
analyze theoretically the system and discover that three phase transitions
compete: a meta-nematic, quasi-1D to 2D transition, where inter-chain
interaction leads to the closing of the Fermi surface; a transition into a
striped phase; and crystallisation of the fermions into a `checkerboard'
\\ ( , 614kb)
Date: Wed, 19 Mar 2008 08:46:39 GMT (77kb)

Title: Double species condensate with tunable interspecies interactions
Authors: G. Thalhammer, G. Barontini, L. De Sarlo, J. Catani, F. Minardi, M.
Categories: cond-mat.other
Comments: 4 pages, 4 figures
   We produce Bose-Einstein condensates of two different species, $^{87}$Rb and
$^{41}$K, in an optical dipole trap in proximity of interspecies Feshbach
resonances. We discover and characterize two Feshbach resonances, located
around 35 and 79 G, by observing the three-body losses and the elastic
cross-section. The narrower resonance is exploited to create a double species
condensate with tunable interactions. Our system opens the way to the
exploration of double species Mott insulators and, more in general, of the
quantum phase diagram of the two species Bose-Hubbard model.
\\ ( , 77kb)
Date: Wed, 19 Mar 2008 14:58:31 GMT (84kb)

Title: Magnetic field-induced one-magnon Raman scattering in the magnon
   Bose-Einstein condensation phase of TlCuCl$_{3}$
Authors: Haruhiko Kuroe, Kouhei Kusakabe, Akira Oosawa, Tomoyuki Sekine, Fumiko
   Yamada, Hidekazu Tanaka, and Masashige Matsumoto
Categories: cond-mat.str-el
Comments: 6 pages, 4 figures
   We report the observation of the $A_{\rm g}$-symmetric one-magnon Raman peak
in the magnon Bose-Einstein condensation phase of TlCuCl$_{3}$. Its Raman shift
traces the one-magnon energy at the magnetic $\Gamma$ point, and its intensity
is proportional to the squared transverse magnetization. The appearance of the
one-magnon Raman scattering originates from the exchange magnon Raman process
and reflects the change of the magnetic-state symmetry. Using the bond-operator
representation, we theoretically clarify the Raman selection rules, being
consistent with the experimental results.
\\ ( , 84kb)
Date: Wed, 19 Mar 2008 17:27:34 GMT (937kb)

Title: Rise and fall of hidden string order of lattice bosons
Authors: Erez Berg, Emanuele G. Dalla Torre, Thierry Giamarchi and Ehud Altman
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 15 pages, 8 figures
   We investigate the ground state properties of a newly discovered phase of one
dimensional lattice bosons with extended interactions (see E. G. Dalla Torre et
al., Phys. Rev. Lett. \textbf{97}, 260401 (2006)). The new phase, termed the
Haldane Insulator (HI) in analogy with the gapped phase of spin-1 chains, is
characterized by a non local order parameter, which can only be written as an
infinite string in terms of the bosonic densities. We show that the string
order can nevertheless be probed with physical fields that couple locally, via
the effect those fields have on the quantum phase transitions separating the
exotic phase from the conventional Mott and density wave phases. Using a field
theoretical analysis we show that a perturbation which breaks lattice inversion
symmetry gaps the critical point separating the Mott and Haldane phases and
eliminates the sharp distinction between them. This is remarkable given that
neither of these phases involves broken inversion symmetry. We also investigate
the evolution of the phase diagram with the tunable coupling between parallel
chains in an optical lattice setup. We find that inter-chain tunneling destroys
the direct phase transition between the Mott and Haldane insulators by
establishing an intermediate superfluid phase. On the other hand coupling the
chains only by weak repulsive interactions does not modify the structure of the
phase diagram. The theoretical predictions are confirmed with numerical
calculations using the Density Matrix Renormalization Group (DMRG).
\\ ( , 937kb)
Date: Wed, 19 Mar 2008 18:01:36 GMT (388kb)

Title: Magnetic phases of one-dimensional lattices with 2 to 4 fermions per
Authors: J.-P. Nikkarila, M. Koskinen, S.M. Reimann and M. Manninen
Categories: cond-mat.str-el cond-mat.mes-hall
Comments: 8 pages, 6 figures
   We study the spectral and magnetic properties of one-dimensional lattices
filled with 2 to 4 fermions (with spin 1/2) per lattice site. We use a
generalized Hubbard model that takes account all interactions on a lattice
site, and solve the many-particle problem by exact diagonalization. We find an
intriguing magnetic phase diagram which includes ferromagnetism, spin-one
Heisenberg antiferromagnetism, and orbital antiferromagnetism.
\\ ( , 388kb)
Date: Wed, 19 Mar 2008 18:25:19 GMT (308kb,D)

Title: Shell-Model Monte Carlo Simulations of Pairing in Few-Fermion Systems
Authors: N. T. Zinner, K. M{\o}lmer, C. \"Ozen, K. Langanke, D. J. Dean
Categories: cond-mat.supr-con cond-mat.other
Comments: Revtex format, 4+ pages, 3 figures
   We study a trapped system of fermions with a zero-range two-body interaction
on the BCS side of unitarity using the Shell-Model Monte Carlo method. The
method provides ab initio results in the low N limit where the BCS mean-field
theory is not applicable. The energy and pairing properties are presented as
functions of interaction strength, particle number, and temperature. In the
interesting region where the typical matrix elements of the two-body
interaction is comparable to the level spacing of the trap we find large
odd-even effects and signatures of shell structure. As a function of
temperature, we observe the disappearance of these effects as in a phase
\\ ( , 308kb)
Date: Tue, 18 Mar 2008 19:45:05 GMT (18kb)

Title: Simulation of Many-Body Hamiltonians using Perturbation Theory with
   Bounded-Strength Interactions
Authors: Sergey Bravyi, David P. DiVincenzo, Daniel Loss and Barbara M. Terhal
Categories: quant-ph cond-mat.other math-ph math.MP
Comments: v1: 8 pages Latex, 1 figure
   We show how to map a given n-qubit target Hamiltonian with bounded-strength
k-body interactions onto a simulator Hamiltonian with two-body interactions,
such that the ground-state energy of the target and the simulator Hamiltonians
are the same up to an extensive error O(epsilon n) for arbitrary small epsilon.
The strength of interactions in the simulator Hamiltonian depends on epsilon
and k but does not depend on n. We accomplish this reduction using a new way of
deriving an effective low-energy Hamiltonian which relies on the
Schrieffer-Wolff transformation of many-body physics.
\\ ( , 18kb)
Date: Wed, 19 Mar 2008 09:51:39 GMT (691kb)

Title: Nonlinear spectroscopy of photons bound to one atom
Authors: I. Schuster, A. Kubanek, A. Fuhrmanek, T. Puppe, P.W.H. Pinkse, K.
   Murr and G. Rempe
Categories: quant-ph
Comments: 7 figures, Nature Physics
   Optical nonlinearities typically require macroscopic media, thereby making
their implementation at the quantum level an outstanding challenge. Here we
demonstrate a nonlinearity for one atom enclosed by two highly reflecting
mirrors. We send laser light through the input mirror and record the light from
the output mirror of the cavity. For weak laser intensity, we find the
vacuum-Rabi resonances. But for higher intensities, we find an additional
resonance. It originates from the fact that the cavity can accommodate only an
integer number of photons and that this photon number determines the
characteristic frequencies of the coupled atom-cavity system. We selectively
excite such a frequency by depositing at once two photons into the system and
find a transmission which increases with the laser intensity squared. The
nonlinearity differs from classical saturation nonlinearities and is direct
spectroscopic proof of the quantum nature of the atom-cavity system. It
provides a photon-photon interaction by means of one atom, and constitutes a
step towards a two-photon gateway or a single-photon transistor.
\\ ( , 691kb)
Date: Tue, 18 Mar 2008 21:54:39 GMT (160kb)

Title: Arbitrary Coherent Superpositions of Quantized Vortices in Bose-Einstein
   Condensates from Orbital Angular Momentum Beams of Light
Authors: Sulakshana Thanvanthri, Kishore T. Kapale and Jonathan P. Dowling
Categories: quant-ph
Comments: 13 pages, 11 figures
   We recently proposed a scheme for the creation of coherent superpositions of
vortex states in Bose-Einstein condensates (BEC) using orbital angular momentum
(OAM) states of light [Phys. Rev. Lett. 95, 173601 (2005)]. Here we discuss
further technical details of the proposal, provide alternative,
time-reversal-symmetric scheme for transfer of a superposition of OAM states of
light to the BEC via a procedure analogous to the traditional STimulated Raman
Adiabatic Passage (STIRAP) technique, and discuss an alternative trap
configuration conducive for sustaining large charge vortices. Superpositions of
OAM states of light, created using experimental techniques, can be transfered
to an initially nonrotating BEC via a specially devised Raman coupling scheme.
The techniques proposed here open up avenues to study coherent interaction of
OAM states of light with matter. The study could also be employed for
performing various quantum information processing tasks with OAM states of
light--including a memory for a quantum state of the initial superposition.
\\ ( , 160kb)
Date: Tue, 18 Mar 2008 23:08:29 GMT (745kb)

Title: Real-time control of the periodicity of a standing wave: an optical
Authors: T. C. Li, H. Kelkar, D. Medellin, and M. G. Raizen
Categories: quant-ph
Comments: 6 pages, 6 figures
   We report an experimental method to create optical lattices with real-time
control of their periodicity. We demonstrate a continuous change of the lattice
periodicity from 0.96 $\mu$m to 11.2 $\mu$m in one second, while the center
fringe only moves less than 2.7 $\mu$m during the whole process. This provides
a powerful tool for controlling ultracold atoms in optical lattices, where
small spacing is essential for quantum tunneling, and large spacing enables
single-site manipulation and spatially resolved detection.
\\ ( , 745kb)
Date: Wed, 19 Mar 2008 11:18:27 GMT (507kb)

Title: Simultaneous cooling and entanglement of mechanical modes of a
   micromirror in an optical cavity
Authors: Claudiu Genes, David Vitali and Paolo Tombesi
Categories: quant-ph
Comments: submitted to NJP
   Laser cooling of a mechanical mode of a resonator by the radiation pressure
of a detuned optical cavity mode has been recently demonstrated by various
groups in different experimental configurations. Here we consider the effect of
a second mechanical mode with a close, but different resonance frequency. We
show that the nearby mechanical resonance is simultaneously cooled by the
cavity field, provided that the difference between the two mechanical
frequencies is not too small. When this frequency difference becomes smaller
than the effective mechanical damping of the secondary mode, the two cooling
processes interfere destructively and cavity cooling is suppressed in the limit
of identical mechanical frequencies. We show that also the entanglement
properties of the steady state of the tripartite system crucially depend upon
on the difference between the two mechanical frequencies. If the latter is
larger than the effective damping of the second mechanical mode, the state
shows fully tripartite entanglement and each mechanical mode is entangled with
the cavity mode. If instead the frequency difference is smaller, the steady
state is a two-mode biseparable state, inseparable only when one splits the
cavity mode from the two mechanical modes. In this latter case, the
entanglement of each mechanical mode with the cavity mode is extremely fragile
with respect to temperature.
\\ ( , 507kb)
Date: Wed, 19 Mar 2008 16:02:13 GMT (914kb)

Title: Quantum optics with bosons and fermions
Authors: Alain Aspect (LCFIO), Denis Boiron (LCFIO), Christoph Westbrook
Categories: quant-ph
Comments: English version of "Optique atomique quantique : apr\`es les bosons,
   les fermions"
Proxy: ccsd hal-00265624
Journal-ref: Europhysics News 39, 1 (2008) 25
DOI: 10.1051/epn2008004
   Atom optics, a field which takes much inspiration from traditional optics,
has advanced to the point that some of the fundamental experiments of quantum
optics, involving photon correlations, have found atomic analogs. We discuss
some recent experiments on atom bunching and anti-bunching as well as some
prospects for extending them to the field of many body physics.
\\ ( , 914kb)
Date: Wed, 19 Mar 2008 21:45:58 GMT (38kb)

Title: Canonical Trajectories and Critical Coupling of the Bose-Hubbard
   Hamiltonian in a Harmonic Trap
Authors: G.G. Batrouni, H. R. Krishnamurthy, K. W. Mahmud, V.G. Rousseau, R.T.
Categories: cond-mat.other cond-mat.stat-mech
   Quantum Monte Carlo (QMC) simulations and the Local Density Approximation
(LDA) are used to map the constant particle number (canonical) trajectories of
the Bose Hubbard Hamiltonian confined in a harmonic trap onto the $(\mu/U,t/U)$
phase diagram of the uniform system. Generically, these curves do not intercept
the tips of the Mott insulator (MI) lobes of the uniform system. This
observation necessitates a clarification of the appropriate comparison between
critical couplings obtained in experiments on trapped systems with those
obtained in QMC simulations. The density profiles and visibility are also
obtained along these trajectories. Density profiles from QMC in the confined
case are compared with LDA results.
\\ ( , 38kb)
Date: Thu, 20 Mar 2008 03:17:19 GMT (699kb)

Title: Theory of correlations between ultra-cold bosons released from an
   optical lattice
Authors: E. Toth, A. M. Rey and P. B. Blakie
Categories: cond-mat.other
Comments: 18 pages, 11 figures
   In this paper we develop a theoretical description of the correlations
between ultra-cold bosons after free expansion from confinement in an optical
lattice. We consider the system evolution during expansion and give criteria
for a far field regime. We develop expressions for first and second order
two-point correlations based on a variety of commonly used approximations to
the many-body state of the system including Bogoliubov, meanfield decoupling,
and particle-hole perturbative solution about the perfect Mott-insulator state.
Using these approaches we examine the effects of quantum depletion and pairing
on the system correlations. Comparison with the directly calculated correlation
functions is used to justify a Gaussian form of our theory from which we
develop a general three-dimensional formalism for inhomogeneous lattice
\\ ( , 699kb)
Date: Thu, 20 Mar 2008 09:23:51 GMT (399kb,D)

Title: Spreading of correlations and entanglement after a quench in the
   Bose-Hubbard model
Authors: Andreas Laeuchli, Corinna Kollath
Categories: cond-mat.other
Comments: 19 pages, 9 figures
   We investigate the spreading of information in a Bose-Hubbard system after a
sudden parameter change. In particular, we study the time-evolution of
correlations and entanglement following a quench. The investigated quantities
show a light-cone like evolution, i.e. the spreading with a finite velocity. We
discuss the relation of this veloctiy to other characteristic velocities of the
system, like the sound velocity. The entanglement is investigated using two
different measures, the von-Neuman entropy and mutual information. Whereas the
von-Neumann entropy grows rapidly with time the mutual information can as well
decrease after an initial increase. Additionally we show that the static von
Neuman entropy characterises the location of the quantum phase transition.
\\ ( , 399kb)
Date: Thu, 20 Mar 2008 13:47:49 GMT (125kb)

Title: Mode-locking and mode-competition in a non-equilibrium solid-state
Authors: P. R. Eastham
Categories: cond-mat.other cond-mat.str-el
Comments: 5 pages, 2 figures
   A trapped polariton condensate with continuous pumping and decay is analyzed
using a generalized Gross-Pitaevskii model. Whereas an equilibrium condensate
is characterized by a macroscopic occupation of a ground state, here the
steady-states take more general forms. Some are characterized by a large
population in an excited state, and others by large populations in several
states. In the latter case, the highly-populated states synchronize to a common
frequency above a critical density. Estimates for the critical density of this
synchronization transition are consistent with experiments.
\\ ( , 125kb)
Date: Thu, 20 Mar 2008 17:45:56 GMT (27kb)

Title: The Nonlinear Dirac Equation in Bose-Einstein Condensates: Foundation
   and Symmetries
Authors: L. H. Haddad and L. D. Carr
Categories: cond-mat.other
Comments: 11 pages, 1 figure
   We show that Bose-Einstein condensates in a honeycomb optical lattice are
described by a nonlinear Dirac equation in the long wavelength, mean field
limit. Unlike nonlinear Dirac equations posited by particle theorists, which
are designed to preserve the principle of relativity, i.e., Poincar\'e
covariance, the nonlinear Dirac equation for Bose-Einstein condensates breaks
this symmetry. We present a rigorous derivation of the nonlinear Dirac equation
from first principles. We provide a thorough discussion of all symmetries
broken and maintained.
\\ ( , 27kb)

The replacements:

replaced with revised version Fri, 14 Mar 2008 05:03:01 GMT (188kb)

Title: Solitons in two-dimensional Bose-Einstein condensates
Authors: Shunji Tsuchiya, Franco Dalfovo, Lev P. Pitaevskii
Categories: cond-mat.supr-con cond-mat.other
Comments: 4 pages, 4 figures, revised version
\\ ( , 188kb)
replaced with revised version Sat, 15 Mar 2008 09:35:47 GMT (71kb)

Title: Finite Size Effect on Bose-Einstein Condensation
Authors: Shyamal Biswas
Categories: cond-mat.stat-mech astro-ph
Comments: Ph.D. Thesis
\\ ( , 71kb)
replaced with revised version Mon, 17 Mar 2008 10:52:12 GMT (43kb)

Title: Macroscopic Periodic Tunneling of Fermi Atoms in the BCS-BEC Crossover
Authors: L. Salasnich, N. Manini and F. Toigo
Categories: cond-mat.stat-mech cond-mat.soft cond-mat.supr-con
Comments: 6 pages 3 figures revtex
\\ ( , 43kb)
replaced with revised version Sat, 15 Mar 2008 16:53:47 GMT (59kb)

Title: The model of interacting spatial permutations and its relation to the
   Bose gas
Authors: Daniel Ueltschi
Categories: cond-mat.stat-mech math-ph math.MP
Comments: 14 pages
\\ ( , 59kb)
arXiv:0802.3972 (*cross-listing*)
replaced with revised version Mon, 17 Mar 2008 13:59:14 GMT (196kb)

Title: Exotic quantum phase transitions in a Bose-Einstein condensate coupled
   to an optical cavity
Authors: Gang Chen, Xiaoguang Wang, J.-Q. Liang, and Z. D. Wang
Categories: quant-ph cond-mat.other physics.atom-ph
Comments: 4 pages; figures 1 and 3 are modified; topos are corrected
\\ ( , 196kb)
replaced with revised version Mon, 17 Mar 2008 14:01:08 GMT (280kb)

Title: Observation of Ultra-narrow Electromagnetically Induced Transparency and
   Slow Light using Purely Electronic Spins in a Hot Atomic Vapor
Authors: F. Goldfarb, J. Ghosh, M. David, J. Ruggiero, T. Chaneli\`ere, J.-L.
   Le Gou\"et, H. Gilles, R. Ghosh, and F. Bretenaker
Categories: quant-ph
\\ ( , 280kb)
replaced with revised version Tue, 18 Mar 2008 10:42:58 GMT (391kb)

Title: Creation of resilient entangled states and a resource for
   measurement-based quantum computation with optical superlattices
Authors: B. Vaucher, A. Nunnenkamp, and D. Jaksch
Categories: cond-mat.other quant-ph
Comments: 23 pages, 6 figures, IOP style, published in New Journal of Physics.
   Minor corrections/few typos removed
Journal-ref: New J. Phys. 10, 023005 (2008)
DOI: 10.1088/1367-2630/10/2/023005
\\ ( , 391kb)
replaced with revised version Mon, 17 Mar 2008 21:35:42 GMT (59kb)

Title: Collective Excitations of Trapped Imbalanced Fermion Gases
Authors: Achilleas Lazarides and Bert Van Schaeybroeck
Categories: cond-mat.other cond-mat.stat-mech
Comments: 4 pages; accepted for publication in PRA
\\ ( , 59kb)
replaced with revised version Tue, 18 Mar 2008 14:59:30 GMT (27kb)

Title: Quasiparticles, coherence and nonlinearity: exact simulations of
   RF-spectroscopy of strongly interacting one-dimensional Fermi gases
Authors: M. J. Leskinen, V. Apaja, J. Kajala, P. Torma
Categories: cond-mat.supr-con cond-mat.other
Comments: 4 pages, 3 figures
\\ ( , 27kb)
replaced with revised version Tue, 18 Mar 2008 16:43:25 GMT (14kb)

Title: Quantum origin of quantum jumps: Breaking of unitary symmetry induced by
   information transfer and the transition from quantum to classical
Authors: Wojciech Hubert Zurek
Categories: quant-ph cond-mat.stat-mech hep-th
Comments: For comments see Seth Lloyd, NATURE 450, 1167 (2007)
Journal-ref: Phys. Rev. A 76, 052110 (2007)
\\ ( , 14kb)
replaced with revised version Wed, 19 Mar 2008 14:21:19 GMT (256kb)

Title: Hanbury Brown and Twiss correlations in atoms scattered from colliding
Authors: Klaus Molmer, A. Perrin, V. Krachmalnicoff, V. Leung, D. Boiron, A.
   Aspect, C. I. Westbrook
Categories: cond-mat.other quant-ph
Comments: Minor corrections. reference updated
Journal-ref: Phys. Rev. A 77, 033601 (2008);
\\ ( , 256kb)
replaced with revised version Wed, 19 Mar 2008 09:13:34 GMT (112kb,D)

Title: Self-organization of a Bose-Einstein condensate in an optical cavity
Authors: D. Nagy, G. Szirmai, P. Domokos
Categories: quant-ph cond-mat.other
Comments: 11 pages, final version. Accepted for publication in EPJD
\\ ( , 112kb)
replaced with revised version Thu, 20 Mar 2008 10:31:28 GMT (217kb)

Title: Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a
   harmonic trap
Authors: C. Klempt, T. Henninger, O. Topic, J. Will, St. Falke, W. Ertmer, and
   J. Arlt
Categories: cond-mat.other
Comments: 7 pages, 8 figures
\\ ( , 217kb)
replaced with revised version Wed, 19 Mar 2008 20:32:00 GMT (467kb)

Title: Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
Authors: Roberto B. Diener, Rajdeep Sensarma, Mohit Randeria
Categories: cond-mat.other cond-mat.supr-con
Comments: 23 pages, 11 figures
Journal-ref: Physical Review A 77, 023626 (2008)
DOI: 10.1103/PhysRevA.77.023626
\\ ( , 467kb)
replaced with revised version Thu, 20 Mar 2008 18:52:28 GMT (93kb)

Title: Spin density-functional theory for imbalanced interacting Fermi gases in
   highly elongated harmonic traps
Authors: Gao Xianlong and Reza Asgari
Categories: cond-mat.str-el
Comments: Minor corrections, three references added, Phys. Rev. A 77, 033604
\\ ( , 93kb)

Till next time,

Dr M. J. Davis,               Senior Lecturer in Physics
School of Physical Sciences,  email:
University of Queensland,     ph   : +61 7 334 69824
Brisbane, QLD 4072,           fax  : +61 7 336 51242
Matt's arXiv selection: weekly summary of cold-atom papers from
Legal stuff: Unless stated otherwise, this e-mail represents only the
views of the sender and not the views of the University of Queensland
Received on Thu Apr 03 2008 - 09:47:57 EST

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