[Matts-arxiv] Matt's arXiv selection: week ending 9 October 2009

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Thu, 14 Jan 2010 17:37:16 +1000

Dear subscribers,

A happy new year to you all. It has been a fairly long absence, and there is a
fair bit of ground to catch up - we currently about three months behind. But we
haven't been entirely idle in the meantime: Chao Feng has authored a neat little
piece of software that allows the compilation of each weekly email to be sped up
by a factor of two. Over the next week or two I hope we will get back up to
speed, and we can start the new year as we intend to go on.

This week's selection was compiled by a Geoff Lee, and contains 16 new abstracts
and 5 replacements.

arXiv:0910.0016 (*cross-listing*)
Date: Wed, 30 Sep 2009 20:13:03 GMT (1836kb)

Title: Long-distance entanglement in many-body atomic and optical systems
Authors: Salvatore M. Giampaolo, Fabrizio Illuminati
Categories: quant-ph cond-mat.other
Comments: 15 pages,
   We discuss the phenomenon of long-distance entanglement in the ground state
of quantum spin models, its use in high-fidelity and robust quantum
communication, and its realization in many-body systems of ultracold atoms in
optical lattices and in arrays of coupled optical cavities. We investigate
different patterns of site-dependent interaction couplings, singling out two
general settings: Patterns that allow for perfect long-distance entanglement
(LDE) in the ground state of the system, namely such that the end-to-end
entanglement remains finite in the thermodynamic limit, and patterns of quasi
long-distance entanglement (QLDE) in the ground state of the system, namely,
such such that the end-to-end entanglement vanishes with a very slow power-law
decay as the length of the spin chain is increased. We discuss physical
realizations of these models in ensembles of ultracold bosonic atoms loaded in
optical lattices. We show how, using either suitably engineered super-lattice
structures or exploiting the presence of edge impurities in lattices with
single periodicity, it is possible to realize models endowed with nonvanishing
LDE or QLDE. We then study how to realize models that optimize the robustness
of QLDE at finite temperature and in the presence of imperfections using
suitably engineered arrays of coupled optical cavities. We finally introduce
LDE-based schemes of long-distance quantum teleportation in linear arrays of
coupled cavities and show that they allow for high-fidelity and high success
rates even at moderately high temperatures.
\\ ( http://arxiv.org/abs/0910.0016 , 1836kb)
Date: Thu, 1 Oct 2009 20:00:09 GMT (75kb)

Title: Theory of Magnetic Field-Induce Bose-Einstein Condensation of Triplons
   in Ba3Cr2O8
Authors: Tyler Dodds, Bohm-Jung Yang, and Yong Baek Kim
Categories: cond-mat.str-el
Comments: 10 pages, 13 figures
   Motivated by recent experiments on Ba$_{3}$Cr$_{2}$O$_8$, a new spin-dimer
compound with spin-1/2 moments of Cr$^{5+}$ ions, we theoretically investigate
the field-induced magnetic ordering in this material in view of the
Bose-Einstein condensation (BEC) of triplet excitations (triplons). We apply
the self-consistent Hartree-Fock-Popov (HFP) approach to a microscopic
Hamiltonian, using the realistic triplon dispersion measured in an inelastic
neutron scattering experiment. In particular, we ask to what extent the BEC of
dilute triplons near the critical field can explain the magnetic ordering in
this material. For example, we investigate the temperature range where the BEC
picture of triplons can be applied via the HFP approach. We also determine the
temperature regime where a quadratic approximation of the triplon dispersion
works. It is found that the strength of the effective repulsive interaction
between triplons is much weaker in Ba$_{3}$Cr$_{2}$O$_8$ than in the canonical
spin-dimer compound TlCuCl$_{3}$. Small effective repulsive interaction in
combination with the narrow band of triplons leads to higher density of
triplons $n_{cr}$ at the critical point. It turns out that the combined effect
points to a bigger HFP correction $U n_{cr}$ in Ba$_3$Cr$_2$O$_8$ than in
TlCuCl$_{3}$. Nonetheless, the HFP approach provides a reasonable explanation
of the transverse magnetization and the specific heat data of
\\ ( http://arxiv.org/abs/0910.0247 , 75kb)
Date: Fri, 2 Oct 2009 05:05:15 GMT (265kb)

Title: Fast-forward of adiabatic dynamics in quantum mechanics
Authors: Shumpei Masuda and Katsuhiro Nakamura
Categories: cond-mat.mes-hall
   We propose a way to accelerate adiabatic dynamics of wave functions in
quantum mechanics to obtain a final adiabatic state except for the spatially
uniform phase in any desired short time. We develop the previous theory of
fast-forward (Masuda & Nakamura 2008) so as to derive a driving potential for
the fast-forward of the adiabatic dynamics. A typical example is the
fast-forward of adiabatic transport of a wave function which is the ideal
transport in the sense that a stationary wave function is transported to an
aimed position in any desired short time without leaving any disturbance at the
final time of the fast-forward. As other important examples we show accelerated
manipulations of wave functions such as their splitting and squeezing. The
theory is also applicable to macroscopic quantum mechanics described by the
nonlinear Schroedinger equation.
\\ ( http://arxiv.org/abs/0910.0301 , 265kb)
Date: Fri, 2 Oct 2009 15:14:49 GMT (14kb)

Title: Effects of disorder on quantum fluctuations and superfluid density of a
   Bose-Einstein condensate in a two-dimensional optical lattice
Authors: Ying Hu, Zhaoxin Liang, and Bambi Hu
Categories: cond-mat.quant-gas cond-mat.dis-nn
Comments: 8 pages, 0 figure. To appear in Physical Review A
   We investigate a Bose-Einstein condensate trapped in a 2D optical lattice in
the presence of weak disorder within the framework of the Bogoliubov theory. In
particular, we analyze the combined effects of disorder and an optical lattice
on quantum fluctuations and superfluid density of the BEC system. Accordingly,
the analytical expressions of the ground state energy and quantum depletion of
the system are obtained. Our results show that the lattice still induces a
characteristic 3D to 1D crossover in the behavior of quantum fluctuations,
despite the presence of weak disorder. Furthermore, we use the linear response
theory to calculate the normal fluid density of the condensate induced by
disorder. Our results in the 3D regime show that the combined presence of
disorder and lattice induce a normal fluid density that asymptotically
approaches 4/3 of the corresponding condensate depletion. Conditions for
possible experimental realization of our scenario are also proposed.
\\ ( http://arxiv.org/abs/0910.0419 , 14kb)
Date: Sat, 3 Oct 2009 08:54:11 GMT (356kb)

Title: D-wave bosonic pair in an optical lattice
Authors: Zi Cai, Lei Wang, Jian Li, Shu Chen, X. C. Xie, Yupeng Wang
Categories: cond-mat.quant-gas cond-mat.str-el
Comments: 5 pages, 5 figures
   We present a bosonic model, in which two bosons may form a bound pair with
d-wave symmetry via the four-site ring exchange interaction. A d-wave pairing
superfluid as well as a d-wave density wave (DDW) state, are proposed to be
achievable in this system. This exotic bosonic system can be realized in the
BEC zone of a two-dimensional attractive p-band spinless fermionic system. By
the mean field approach, we find that at low densities, the d-wave pairs may
condensate, leading to a d-wave bosonic paired superfluid. At some particular
filling factors, a novel phase, d-wave density wave state, emerges. We study
this DDW state and its corresponding quantum phase transition in a two-leg
ladder by the time-evolving block decimation (TEBD) method.
\\ ( http://arxiv.org/abs/0910.0508 , 356kb)
Date: Mon, 5 Oct 2009 14:48:47 GMT (911kb)

Title: Adjustable microchip ring trap for cold atoms and molecules
Authors: Paul M. Baker, James A. Stickney, Matthew B. Squires, James A.
   Scoville, Evan J. Carlson, Walter R. Buchwald, Steven M. Miller
Categories: physics.atom-ph
   We describe the design and function of a circular magnetic waveguide for
deBroglie waves produced from wires on a microchip. The guide is a
two-dimensional magnetic minimum for trapping weak-field seeking states of
atoms or molecules with a magnetic dipole moment. The design consists of seven
circular wires sharing a common radius. We describe the design, the
time-dependent currents of the wires and show that it is possible to form a
circular waveguide with adjustable height and gradient while minimizing
perturbation resulting from leads or wire crossings. This maximal area geometry
is suited for rotation sensing with atom interferometry via the Sagnac effect
using either cold atoms, molecules and Bose-condensed systems.
\\ ( http://arxiv.org/abs/0910.0564 , 911kb)
Date: Mon, 5 Oct 2009 17:26:24 GMT (403kb)

Title: Bose-Einstein Condensation of Strontium
Authors: Simon Stellmer, Meng Khoon Tey, Bo Huang, Rudolf Grimm, Florian
Categories: cond-mat.quant-gas
Comments: 4 pages, 3 figures
   We report on the attainment of Bose-Einstein condensation (BEC) with
ultracold strontium atoms. We use the 84Sr isotope, which has a low natural
abundance but offers excellent scattering properties for evaporative cooling.
Based on the three efficient stages of accumulation in a metastable state using
a magnetic trap, narrow-line cooling, and straightforward evaporative cooling
in an optical trap, we obtain pure condensates containing 1.5x10^5 atoms. This
puts 84Sr in a prime position for future experiments on quantum-degenerate
gases of atomic two-electron systems.
\\ ( http://arxiv.org/abs/0910.0634 , 403kb)
Date: Sun, 4 Oct 2009 22:22:39 GMT (34kb)

Title: Finite-Temperature Properties of Attractive Three-Component Fermionic
   Atoms in Optical Lattices
Authors: Kensuke Inaba and Sei-ichiro Suga
Categories: cond-mat.quant-gas cond-mat.supr-con
Comments: 4 pages, 4 figures
   We investigate the finite-temperature properties of attractive
three-component (colors) fermionic atoms in optical lattices using a
self-energy functional approach. As the strength of the attractive interaction
increases in the low-temperature region, we observe a second-order transition
from a Fermi liquid to a color superfluid (CSF), where atoms from two of the
three colors form Cooper pairs. In the strong attractive region, we observe a
first-order transition from a CSF to a trionic state, where three atoms with
different colors form singlet bound states. A crossover between a Fermi liquid
and a trionic state is observed in the high-temperature region. We present a
phase diagram covering zero to finite temperatures. We demonstrate that the CSF
transition temperature is enhanced by the anisotropy of the attractive
\\ ( http://arxiv.org/abs/0910.0648 , 34kb)
Date: Mon, 5 Oct 2009 10:55:11 GMT (32kb)

Title: Ultracold atoms at unitarity within quantum Monte Carlo
Authors: Andrew J. Morris, P. Lopez Rios and R. J. Needs
Categories: cond-mat.quant-gas
   Variational and diffusion quantum Monte Carlo (VMC and DMC) calculations of
the properties of the zero-temperature fermionic gas at unitarity are reported.
The ratio of the energy of the interacting to the non-interacting gas for a
system of 128 particles is calculated to be 0.4517(3) in VMC and 0.4339(1) in
the more accurate DMC method. The spherically-averaged pair-correlation
functions, momentum densities, and one-body density matrices are very similar
in VMC and DMC, but the two-body density matrices and condensate fractions show
some differences. Our best estimate of the condensate fraction of 0.51 is a
little smaller than values from other quantum Monte Carlo calculations.
\\ ( http://arxiv.org/abs/0910.0720 , 32kb)
arXiv:0910.0788 (*cross-listing*)
Date: Mon, 5 Oct 2009 15:18:00 GMT (2015kb)

Title: Macroscopic entanglement between a Bose Einstein condensate and a
   superconducting loop
Authors: Mandip Singh
Categories: quant-ph cond-mat.quant-gas
Comments: 11 pages, 5 figures
Journal-ref: Optics Express, Vol. 17, Issue 4, pp. 2600-2610 (2009)
DOI: 10.1364/OE.17.002600
   We theoretically study macroscopic entanglement between a magnetically
trapped Bose-Einstein condensate and a superconducting loop. We treat the
superconducting loop in a quantum superposition of two different flux states
coupling with the magnetic trap to generate macroscopic entanglement. The
scheme also provides a platform to investigate interferometry with an entangled
Bose Einstein condensate and to explore physics at the quantum-classical
\\ ( http://arxiv.org/abs/0910.0788 , 2015kb)
Date: Tue, 6 Oct 2009 09:21:32 GMT (2598kb)

Title: Dynamics of reflection of ultracold atoms from a periodic 1D magnetic
   lattice potential
Authors: Mandip Singh, Russell McLean, Andrei Sidorov and Peter Hannaford
Categories: cond-mat.other physics.atom-ph quant-ph
Comments: 15 pages, 11 figures
Journal-ref: Phys. Rev. A 79, 053407 (2009)
DOI: 10.1103/PhysRevA.79.053407
   We report on an experimental study of the dynamics of the reflection of
ultracold atoms from a periodic one-dimensional magnetic lattice potential. The
magnetic lattice potential of period 10 \textmu m is generated by applying a
uniform bias magnetic field to a microfabricated periodic structure on a
silicon wafer coated with a multilayered TbGdFeCo/Cr magneto-optical film. The
effective thickness of the magnetic film is about 960 nm. A detailed study of
the profile of the reflected atoms as a function of externally induced periodic
corrugation in the potential is described. The effect of angle of incidence is
investigated in detail. The experimental observations are supported by
numerical simulations.
\\ ( http://arxiv.org/abs/0910.0953 , 2598kb)
Date: Tue, 6 Oct 2009 15:44:42 GMT (2184kb)

Title: Cold and Ultracold Rydberg Atoms in Strong Magnetic Fields
Authors: T. Pohl, H. R. Sadeghpour, and P. Schmelcher
Categories: physics.atom-ph
Comments: 46 pages, 38 figures, to appear in Physics Reports
   Cold Rydberg atoms exposed to strong magnetic fields possess unique
properties which open the pathway for an intriguing many-body dynamics taking
place in Rydberg gases consisting of either matter or anti-matter systems. We
review both the foundations and recent developments of the field in the cold
and ultracold regime where trapping and cooling of Rydberg atoms have become
possible. Exotic states of moving Rydberg atoms such as giant dipole states are
discussed in detail, including their formation mechanisms in a strongly
magnetized cold plasma. Inhomogeneous field configurations influence the
electronic structure of Rydberg atoms, and we describe the utility of
corresponding effects for achieving tightly trapped ultracold Rydberg atoms. We
review recent work on large, extended cold Rydberg gases in magnetic fields and
their formation in strongly magnetized ultracold plasmas through collisional
recombination. Implications of these results for current antihydrogen
production experiments are pointed out, and techniques for trapping and cooling
of such atoms are investigated.
\\ ( http://arxiv.org/abs/0910.1037 , 2184kb)
Date: Tue, 6 Oct 2009 18:58:20 GMT (156kb)

Title: Radiative lifetime measurements of rubidium Rydberg states
Authors: Drew B. Branden, Tamas Juhasz, Tatenda Mahlokozera, Cristian Vesa, Roy
   O. Wilson, Mao Zheng, Andrew Kortyna and Duncan A. Tate
Categories: physics.atom-ph
Comments: 6 figures
   We have measured the radiative lifetimes of ns, np and nd Rydberg states of
rubidium in the range 28 < n < 45. To enable long-lived states to be measured,
our experiment uses slow-moving Rb atoms in a magneto-optical trap (MOT). Two
experimental techniques have been adopted to reduce random and systematic
errors. First, a narrow-bandwidth pulsed laser is used to excite the target
Rydberg state, resulting in minimal shot-to-shot variation in the initial state
population. Second, we monitor the target state population as a function of
time delay from the laser pulse using a short-duration, millimetre-wave pulse
that is resonant with a one- or two-photon transition. We then selectively
field ionize the monitor state, and detect the resulting electrons with a
micro-channel plate. This signal is an accurate mirror of the target state
population, and is uncontaminated by contributions from other states which are
populated by black body radiation. Our results are generally consistent with
other recent experimental results obtained using a less sensitive method, and
are also in excellent agreement with theory.
\\ ( http://arxiv.org/abs/0910.1073 , 156kb)
Date: Thu, 8 Oct 2009 11:24:40 GMT (196kb)

Title: Cooling and Near-equilibrium Dynamics of Atomic Gases Across the
   Superfluid-Mott Insulator Transition
Authors: Chen-Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin
Categories: cond-mat.quant-gas cond-mat.other
   We study near-equilibrium thermodynamics of bosonic atoms in a
two-dimensional optical lattice by ramping up the lattice depth to convert a
superfluid into an inhomogeneous mixture of superfluid and Mott insulator.
Detailed study of in situ density profiles shows that, first, locally adiabatic
ramps do not guarantee global thermal equilibrium. Indeed, full thermalization
for typical parameters only occurs for experiment times which exceed one
second. Secondly, ramping non-adiabatically to the Mott insulator regime can
result in strong localized cooling at short times and global cooling once
equilibrated. For an initial temperature estimated as 20 nK, we observe local
temperatures as low as 1.5 nK, and a final global temperature of 9 nK. Possible
cooling mechanisms include adiabatic decompression, modification of the density
of states near the quantum critical regime, and the Joule-Thomson effect.
\\ ( http://arxiv.org/abs/0910.1382 , 196kb)
Date: Thu, 8 Oct 2009 08:25:28 GMT (683kb)

Title: Rayleigh-Taylor instability and mushroom-pattern formation in a
   two-component Bose-Einstein condensate
Authors: Kazuki Sasaki, Naoya Suzuki, Daisuke Akamatsu, Hiroki Saito
Categories: cond-mat.quant-gas
Comments: 5 pages, 4 figures
   The Rayleigh-Taylor instability at the interface in an immiscible
two-component Bose-Einstein condensate is investigated using the mean-field and
Bogoliubov theories. Rayleigh-Taylor fingers are found to grow from the
interface and mushroom patterns are formed. Quantized vortex rings and vortex
lines are then generated around the mushrooms. The Rayleigh-Taylor instability
and mushroom-pattern formation can be observed in a trapped system.
\\ ( http://arxiv.org/abs/0910.1440 , 683kb)
Date: Thu, 8 Oct 2009 15:48:43 GMT (304kb)

Title: Quantum fluctuations and condensate fraction during the time-of-flight
Authors: Shiang Fang, Ray-Kuang Lee, and Daw-Wei Wang
Categories: cond-mat.quant-gas cond-mat.other
Comments: 4 pages and 3 figures
   The quantum fluctuation effects in the time-of-flight (TOF) experiment for a
condensate released from a one-dimensional optical lattice potential is studied
within the truncated Wigner approximation. By investigating both the spatial
and momentum density distributions, we find that the condensate fraction
decreases as an algebraic function of time and hence cannot be measured in the
standard TOF image due to the interaction effect. We then suggest a scheme to
measure the true condensate fraction during the expansion and estimate its
value inside the optical lattice (before expansion), taking into account both
the finite time and finite interaction effects. Implication to the condensate
expansion in higher dimensional systems is also discussed.
\\ ( http://arxiv.org/abs/0910.1518 , 304kb)

The replacements:

replaced with revised version Fri, 2 Oct 2009 15:32:15 GMT (400kb)

Title: Black-hole radiation in Bose-Einstein condensates
Authors: Jean Macher and Renaud Parentani
Categories: cond-mat.quant-gas gr-qc
Comments: revTeX 4, 55 pages single-column, 19 figures; v2: figure and refs
   added, typos corrected; v3: twocolumn, refs added/updated, new results,
   presentation clarified; v4: usefulness of white holes emphasized
\\ ( http://arxiv.org/abs/0905.3634 , 400kb)
replaced with revised version Sat, 3 Oct 2009 17:39:39 GMT (159kb)

Title: Rayleigh-Taylor instability of binary condensates
Authors: S. Gautam and D. Angom
Categories: cond-mat.quant-gas
Comments: 4 pages, 4figures, Extensive modifications including additional
   figure and equations
\\ ( http://arxiv.org/abs/0908.4336 , 159kb)
replaced with revised version Fri, 2 Oct 2009 08:37:56 GMT (1515kb)

Title: Spin-dependent inelastic collisions in spin-2 Bose-Einstein condensates
Authors: Satoshi Tojo, Taro Hayashi, Tatsuyoshi Tanabe, Takuya Hirano, Yuki
   Kawaguchi, Hiroki Saito, and Masahito Ueda
Categories: cond-mat.quant-gas
Comments: 7 pages, 5 figures
\\ ( http://arxiv.org/abs/0909.0489 , 1515kb)
replaced with revised version Mon, 5 Oct 2009 15:38:54 GMT (2369kb)

Title: Vortex Synchronization in Bose-Einstein Condensates: A Time-Dependent
   Gross-Pitaevskii Equation Approach
Authors: Ryan Barnett, Edward Chen, and Gil Refael
Categories: cond-mat.quant-gas
Comments: 6.1 pages, 3 figures
\\ ( http://arxiv.org/abs/0909.4072 , 2369kb)
replaced with revised version Mon, 5 Oct 2009 20:17:59 GMT (28kb,D)

Title: A scalable Bose-Einstein condensate Sagnac interferometer in a linear
Authors: J. H. T. Burke and C. A. Sackett
Categories: cond-mat.quant-gas
Comments: 4 pages, 2 figures. Added references
\\ ( http://arxiv.org/abs/0910.0182 , 28kb)

Till next time,

Dr M. J. Davis,                      Associate Professor in Physics
School of Mathematics and Physics,   ph  : +61 7 334 69824
The University of Queensland,        fax : +61 7 336 51242
Brisbane, QLD 4072,                  mdavis_at_physics.uq.edu.au
Australia.                           www.physics.uq.edu.au/people/mdavis/
Matt's arXiv selection: weekly summary of cold-atom papers from arXiv.org
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