# Matt's arXiv selection: week ending 17 August 2007.

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Fri, 24 Aug 2007 16:11:38 +1000 (EST)

The following message was sent to the matts_arxiv list by Matthew Davis <mdavis_at_physics.uq.edu.au>

Another slow week with 12 new papers and 7 replacements... I guess everyone was
on holiday/at a conference...

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arXiv:0708.1386
Date: Fri, 10 Aug 2007 09:31:58 GMT (232kb)

Title: Quantum computing with collective ensembles of multi-level systems
Authors: E. Brion, K. Moelmer and M. Saffman
Categories: quant-ph
\\
We propose a new physical approach for encoding and processing of quantum
information in ensembles of multi-level quantum systems, where the different
bits are not carried by individual particles but associated with the collective
population of different internal levels. One- and two-bit gates are implemented
by collective internal state transitions taking place in the presence of an
excitation blockade mechanism which restricts the population of each internal
state to the values zero and unity. 10-20 bit quantum computers can be built
via this scheme in single trapped clouds of ground state atoms subject to the
Rydberg excitation blockade mechanism, and the linear dependence between
register size and the number of internal quantum states in atoms offers
realistic means to reach larger registers.
\\ ( http://arxiv.org/abs/0708.1386 , 232kb)
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arXiv:0708.1390
Date: Fri, 10 Aug 2007 09:54:42 GMT (757kb)

Title: Non-linear optics with two trapped atoms
Authors: Sonia Fern\'andez-Vidal, Stefano Zippilli, and Giovanna Morigi
Categories: quant-ph
\\
We show theoretically that two atomic dipoles in a resonator constitute a
non-linear medium, whose properties can be controlled through the relative
position of the atoms inside the cavity and the detuning and intensity of the
driving laser. We identify the parameter regime where the system operates as a
parametric amplifier, based on the cascade emission of the collective dipole of
the atoms, and determine the corresponding spectrum of squeezing of the field
at the cavity output. This dynamics could be observed as a result of
self-organization of laser-cooled atoms in resonators.
\\ ( http://arxiv.org/abs/0708.1390 , 757kb)
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arXiv:0708.1743
Date: Mon, 13 Aug 2007 18:07:26 GMT (247kb,D)

Title: Production of long-lived atomic vapor inside high-density buffer gas
Authors: A. O. Sushkov, D. Budker
Categories: physics.atom-ph
\\
Atomic vapor of four different paramagnetic species: gold, silver, lithium,
and rubidium, is produced and studied inside several buffer gases: helium,
nitrogen, neon, and argon. The paramagnetic atoms are injected into the buffer
gas using laser ablation. 50-$\mu$m-diameter wires are used as ablation targets
for gold and silver, bulk targets are used for lithium and rubidium. The buffer
gas cools and confines the ablated atoms, slowing down their transport to the
cell walls. Buffer gas temperatures between 20 K and 295 K, and densities
between $10^{16}$ cm$^{-3}$ and $2\times10^{19}$ cm$^{-3}$ are explored. Peak
paramagnetic atom densities of $10^{11}$ cm$^{-3}$ are routinely achieved. The
longest observed paramagnetic vapor density decay times are 110 ms for silver
at 20 K and 4 ms for lithium at 32 K. The candidates for the limiting
paramagnetic atom loss mechanism are dimer formation and atom loss on sputtered
clusters.
\\ ( http://arxiv.org/abs/0708.1743 , 247kb)
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arXiv:0708.1759
Date: Mon, 13 Aug 2007 19:25:05 GMT (149kb)

Title: Blogging in the physics classroom: A research-based approach to shaping
students' attitudes towards physics
Authors: Gintaras Duda and Katherine Garrett
Categories: physics.ed-ph
\\
Even though there has been a tremendous amount of research done in how to
help students learn physics, students are still coming away missing a crucial
piece of the puzzle: why bother with physics? Students learn fundamental laws
and how to calculate, but come out of a general physics course without a deep
understanding of how physics has transformed the world around them. In other
words, they get the "how" but not the "why". Studies have shown that students
leave introductory physics courses almost universally less excited about the
topic than when they came in. This paper will detail an experiment to address
this problem: a course weblog or "blog" which discusses real-world applications
of physics and engages students in discussion and thinking outside of class.
Student attitudes towards the value of physics were probed using a 26-question
Likert scale survey over the course of four semesters in an introductory
physics course at a comprehensive Jesuit university. We found that students who
did not participate in the blog study generally exhibited a deterioration in
attitude towards physics as seen previously. However, students who read,
commented, and were involved with the blog maintained their initially positive
attitudes towards physics. Student response to the blog was overwhelmingly
positive, with students claiming that the blog made the things we studied in
the classroom come alive for them and seem much more relevant.
\\ ( http://arxiv.org/abs/0708.1759 , 149kb)
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arXiv:0708.1807
Date: Tue, 14 Aug 2007 05:51:15 GMT (235kb)

Title: Supersolids in the Hard-Core Extended Boson Hubbard Model on the Square
Lattice
Authors: Yu-Chun Chen, Roger Melko, Stefan Wessel, Ying-Jer Kao
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: Revtex 4, 4 pages, 5 figures
\\
We study the ground state phases of the hard-core boson Hubbard model on the
square lattice with both nearest- (nn) and next-nearest-neighbor (nnn) hopping
and repulsion, using quantum Monte Carlo methods. We observe supersolids with
checkerboard, striped, and quarter-filled crystal symmetry, when the system is
doped away from commensurate fillings. We also find that the striped supersolid
transitions directly into the quarter-filled supersolid upon doping. In the
striped supersolid phase, while a strong anisotropy in the superfluid density
is observed, the transverse component remains finite, suggesting a
two-dimensional superflow.
\\ ( http://arxiv.org/abs/0708.1807 , 235kb)
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arXiv:0708.1806
Date: Tue, 14 Aug 2007 05:49:15 GMT (117kb)

Title: Precision Test of Mass Ratio Variations with Lattice-Confined Ultracold
Molecules
Authors: T. Zelevinsky, S. Kotochigova and J. Ye
Categories: physics.atom-ph
\\
We propose a precision measurement of time variations of the proton-electron
mass ratio using ultracold molecules in an optical lattice. Vibrational energy
intervals are sensitive to changes of the mass ratio. In contrast to
measurements that use hyperfine-interval-based atomic clocks, the scheme
discussed here is model-independent and does not require separation of time
variations of different physical constants. The possibility of applying the
zero-differential-Stark-shift optical lattice technique is explored to measure
vibrational transitions at high accuracy.
\\ ( http://arxiv.org/abs/0708.1806 , 117kb)
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arXiv:0708.1956
Date: Tue, 14 Aug 2007 21:01:18 GMT (37kb)

Title: Transforming squeezed light into large amplitude Schr\"odinger cat
states
Authors: Anne E. B. Nielsen and Klaus M\olmer
Categories: quant-ph
\\
A quantum superposition of two coherent states of light, a so-called
Schr\"odinger cat, or kitten, state, with small amplitude can be obtained by
subtracting a photon from a squeezed vacuum state. In experiments this
preparation can be made conditioned on the detection of a photon in the field
from a squeezed light source. We propose and analyze an extended measurement
strategy which allows generation of high fidelity cat states with larger
coherent amplitude.
\\ ( http://arxiv.org/abs/0708.1956 , 37kb)
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arXiv:0708.2073
Date: Wed, 15 Aug 2007 17:19:17 GMT (647kb)

Title: Controlled exchange interaction between pairs of neutral atoms in an
optical lattice
Authors: M. Anderlini, P. J. Lee, B. L. Brown, J. Sebby-Strabley, W. D.
Phillips, J. V. Porto
Categories: quant-ph
Journal-ref: Nature 448, 452-456 (2007)
DOI: 10.1038/nature06011
\\
Ultra-cold atoms trapped by light, with their robust quantum coherence and
controllability, provide an attractive system for quantum information
processing and for simulation of complex problems in condensed matter physics.
Many quantum information processing schemes require that individual qubits be
manipulated and deterministically entangled with one another, a process that
would typically be accomplished by controlled, state-dependent, coherent
interactions among qubits. Recent experiments have made progress toward this
goal by demonstrating entanglement among an ensemble of atoms confined in an
optical lattice. Until now, however, there has been no demonstration of a key
operation: controlled entanglement between atoms in isolated pairs. We have
used an optical lattice of double-well potentials to isolate and manipulate
arrays of paired atoms, inducing controlled entangling interactions within each
pair. Our experiment is the first realization of proposals to use controlled
exchange coupling in a system of neutral atoms. Although 87Rb atoms have nearly
state-independent interactions, when we force two atoms into the same physical
location, the wavefunction exchange symmetry of these identical bosons leads to
state-dependent dynamics. We observe repeated interchange of spin between atoms
occupying different vibrational levels, with a coherence time of more than ten
milliseconds. This observation represents the first demonstration of the
essential component of a quantum SWAP gate in neutral atoms. The "half
implementation" of SWAP, the sqrt(SWAP) gate, is entangling, and together with
single qubit rotations form a set of universal gates for quantum computation.
\\ ( http://arxiv.org/abs/0708.2073 , 647kb)
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arXiv:0708.2107
Date: Wed, 15 Aug 2007 21:15:54 GMT (225kb)

Title: Quantum glass phases in the disordered Bose-Hubbard model
Authors: Pinaki Sengupta and Stephan Haas
Categories: cond-mat.dis-nn
Journal-ref: Phys. Rev. Lett. 99, 050403 (2007)
\\
The phase diagram of the Bose-Hubbard model in the presence of off-diagonal
disorder is determined using Quantum Monte Carlo simulations. A sequence of
quantum glass phases intervene at the interface between the Mott insulating and
the Superfluid phases of the clean system. In addition to the standard Bose
glass phase, the coexistence of gapless and gapped regions close to the Mott
insulating phase leads to a novel Mott glass regime which is incompressible yet
gapless. Numerical evidence for the properties of these phases is given in
terms of global (compressibility, superfluid stiffness) and local
(compressibility, momentum distribution) observables.
\\ ( http://arxiv.org/abs/0708.2107 , 225kb)
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arXiv:0708.2128
Date: Thu, 16 Aug 2007 03:41:57 GMT (412kb)

Title: Self-Trapping of Bose-Einstein Condensates in an Optical Lattice: the
Effect of the System Dimension
Authors: Ju-Kui Xue, Ai-Xia Zhang, Jie Liu
Categories: cond-mat.mes-hall
\\
In the present paper, we investigate the dynamics of a Bose-Einstein
condensates (BEC) loaded into an deep optical lattice of 1D, 2D and 3D, both
analytically and numerically. We focus on the self-trapping state and the
effect of the system dimension. Under the tight-binding approximation we obtain
an analytical criterion for the self-trapping state of BEC using time-dependent
variational method. The phase diagram for self-trapping, soliton, breather, or
diffusion of the BEC cloud is obtained accordingly and verified by directly
solving the discrete Gross-Pitaevskii equation (GPE) numerically. In
particular, we find that the criterion and the phase diagrams are modified
dramatically by the dimension of the lattices.
\\ ( http://arxiv.org/abs/0708.2128 , 412kb)
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arXiv:0708.2196
Date: Thu, 16 Aug 2007 13:22:54 GMT (585kb)

Title: Superfluid Dynamics of a Bose-Einstein Condensate in a Quantum Optical
Lattice
Authors: Aranya B Bhattacherjee
Categories: cond-mat.stat-mech
\\
We study the effect of a one dimensional optical lattice in a cavity field
with quantum properties on the superfluid dynamics of a Bose-Einstein
condensate(BEC). In the cavity the influence of atomic backaction and the
external driving pump become important and strongly modify the optical
potential. Due to the strong coupling between the condensate wavefunction and
the cavity modes, the cavity light field develops a band structure. This study
reveals that the pump and the cavity emerges as a new handle to control the
superfluid properties of the BEC.
\\ ( http://arxiv.org/abs/0708.2196 , 585kb)
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arXiv:0708.2234
Date: Thu, 16 Aug 2007 16:00:32 GMT (5kb)

Title: Bose-Einstein condensation of a Knudsen gas
Authors: Kersion Huang
Categories: cond-mat.stat-mech
\\
We reconcile a long-standing controversy regarding the transition temperature
of the Bose-Einstein condensation in a dilute interacting Bose gas, by showing
that there is a crossover between ideal gas and interacting gas. The former
corresponds to a Knudsen (or collisionless) regime, in which the mean-free-path
is much larger than the system dimension, while the latter corresponds to the
opposite hydrodynamic regime. The deviation of the transition temperature from
that of the non-interacting gas is proportional to the square root of a in the
Knudsen regime, and to a in the hydrodynamic regime, where a is the scattering
length. This crossover may be observable in a Bose gas trapped in a potential
or on an optical lattice.
\\ ( http://arxiv.org/abs/0708.2234 , 5kb)
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The replacements:

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arXiv:cond-mat/0305614
replaced with revised version Fri, 10 Aug 2007 05:29:02 GMT (102kb)

Title: Quantum gas-liquid condensation in an attractive Bose gas
Authors: Shun-ichiro Koh
Categories: cond-mat.stat-mech cond-mat.supr-con
Journal-ref: Physical Review E 72,016104(2005)
DOI: 10.1103/PhysRevE.72.016104
\\ ( http://arxiv.org/abs/cond-mat/0305614 , 102kb)
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arXiv:quant-ph/0602025
replaced with revised version Fri, 10 Aug 2007 09:08:16 GMT (226kb)

Title: Macroscopic superpositions of superfluid flows
Authors: David W. Hallwood, Jacob Dunningham, Keith Burnett
Categories: quant-ph
Journal-ref: New J. Phys. 8 (2006) 180
\\ ( http://arxiv.org/abs/quant-ph/0602025 , 226kb)
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arXiv:cond-mat/0611689
replaced with revised version Mon, 13 Aug 2007 17:47:14 GMT (99kb)

Title: Probing $n$-Spin Correlations in Optical Lattices
Authors: Chuanwei Zhang, V. W. Scarola, and S. Das Sarma
Categories: cond-mat.str-el cond-mat.other quant-ph
Journal-ref: Phys. Rev. A. 76, 023605 (2007)
DOI: 10.1103/PhysRevA.76.023605
\\ ( http://arxiv.org/abs/cond-mat/0611689 , 99kb)
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arXiv:cond-mat/0612174
replaced with revised version Sat, 11 Aug 2007 20:42:41 GMT (378kb)

Title: Phase-locking transition of coupled low-dimensional superfluids
Authors: L. Mathey, A. Polkovnikov, and A.H. Castro Neto
Categories: cond-mat.other
Comments: 7 pages, 4 figures, extended discussion
\\ ( http://arxiv.org/abs/cond-mat/0612174 , 378kb)
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arXiv:cond-mat/0305669
replaced with revised version Tue, 14 Aug 2007 06:06:12 GMT (67kb)

Title: Meissner effect in a charged Bose gas with short-range repulsion
Authors: Shun-ichiro Koh
Categories: cond-mat.supr-con cond-mat.stat-mech
Journal-ref: Physical Review B 68,144502(2003)
DOI: 10.1103/PhysRevB.68.144502
\\ ( http://arxiv.org/abs/cond-mat/0305669 , 67kb)
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arXiv:cond-mat/0609374
replaced with revised version Tue, 14 Aug 2007 12:15:47 GMT (448kb)

Title: Bose-Einstein Condensation Temperature of Dipolar Gas in Anisotropic
Harmonic Trap
Authors: Konstantin Glaum, Axel Pelster
Categories: cond-mat.stat-mech
http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir
Journal-ref: Physical Review A 76, 023604 (2007)
\\ ( http://arxiv.org/abs/cond-mat/0609374 , 448kb)
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arXiv:0705.0671
replaced with revised version Tue, 14 Aug 2007 15:38:58 GMT (54kb)

Title: BEC-BCS Crossover of a Trapped Two-Component Fermi Gas with Unequal
Masses
Authors: J. von Stecher, C. H. Greene, D. Blume
Categories: cond-mat.other
Comments: 11 pages, 6 figures, extended version
\\ ( http://arxiv.org/abs/0705.0671 , 54kb)
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arXiv:0706.4260
replaced with revised version Tue, 14 Aug 2007 11:26:31 GMT (346kb)

Title: Ultracold Bose gases in time-dependent 1D superlattices: response and
quasimomentum structure
Authors: Markus Hild, Felix Schmitt, Ilona T\"urschmann, Robert Roth
Categories: cond-mat.stat-mech
\\ ( http://arxiv.org/abs/0706.4260 , 346kb)
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--
=========================================================================
Dr M. J. Davis,               Senior Lecturer in Physics
School of Physical Sciences,  email: mdavis_at_physics.uq.edu.au
University of Queensland,     ph   : +61 7 334 69824
Brisbane, QLD 4072,           fax  : +61 7 336 51242
Australia.                    http://www.physics.uq.edu.au/people/mdavis/
=========================================================================
Matt's arXiv selection: weekly summary of cold-atom papers from arXiv.org
http://www.physics.uq.edu.au/people/mdavis/matts_arXiv/
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Received on Fri Aug 24 2007 - 16:11:38 EST

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