# Matt's arXiv selection: week ending 20th April 2007.

From: Matthew Davis <mdavis_at_physics.uq.edu.au>
Date: Fri, 27 Apr 2007 15:27:55 +1000 (EST)

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

You can tell I've been busy as the arXiv selection is late again. This
week we have 31 new abstracts and 10 replacements.

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arXiv:0704.1708
Date: Fri, 13 Apr 2007 07:30:52 GMT (59kb)

Title: Is there least action principle in stochastic dynamics?
Authors: Qiuping A. Wang (ISMANS)
Categories: cond-mat.stat-mech
Proxy: ccsd hal-00141482
\\
On the basis of the work showing that the maximum entropy principle for
equilibrium mechanical system is a consequence of the principle of virtual
work, i.e., the virtual work of random forces on a mechanical system should
vanish in thermodynamic equilibrium, we present in this paper a development of
the same principle for the dynamical system out of equilibrium. One of the
objectives of the present work is to justify a least action principle we
postulated previously for stochastic mechanical systems.
\\ ( http://arxiv.org/abs/0704.1708 , 59kb)
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arXiv:0704.1735
Date: Fri, 13 Apr 2007 11:25:00 GMT (16kb)

Title: Calorimetry of Bose-Einstein condensates
Authors: P. B. Blakie, E. Toth, M. J. Davis
Categories: cond-mat.other
\\
We outline a practical scheme for measuring the thermodynamic properties of a
Bose-Einstein condensate as a function of internal energy. We propose using
Bragg scattering and controlled trap manipulations to impart a precise amount
of energy to a near zero temperature condensate. After thermalisation the
temperature can be measured using standard techniques to determine the state
equation $T(U,N,\omega)$. Our analysis accounts for interaction effects and the
excitation of constants of motion which restrict the energy available for
thermalisation.
\\ ( http://arxiv.org/abs/0704.1735 , 16kb)
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arXiv:0704.1804
Date: Fri, 13 Apr 2007 18:09:58 GMT (100kb)

Title: Equation of state of atomic systems beyond s-wave determined by the
lowest order constrained variational method: Large scattering length limit
Authors: Ryan M. Kalas, D. Blume
Categories: cond-mat.other
\\
Dilute Fermi systems with large s-wave scattering length a_s exhibit
universal properties if the interparticle spacing r_o greatly exceeds the range
of the underlying two-body interaction potential. In this regime, r_o is the
only relevant length scale and observables such as the energy per particle
depend only on r_o (or, equivalently, the energy E_{FG} of the free Fermi gas).
This paper investigates Bose and Fermi systems with non-vanishing angular
momentum l using the lowest order constrained variational method. We focus on
the regime where the generalized scattering length becomes large and determine
the relevant length scales. For Bose gases with large generalized scattering
lengths, we obtain simple expressions for the energy per particle in terms of a
l-dependent length scale \xi_l, which depends on the range of the underlying
two-body potential and the average interparticle spacing. We discuss possible
implications for dilute two-component Fermi systems with finite l. Furthermore,
we determine the equation of state of liquid and gaseous bosonic helium.
\\ ( http://arxiv.org/abs/0704.1804 , 100kb)
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arXiv:0704.1686
Date: Fri, 13 Apr 2007 02:54:37 GMT (757kb)

Title: Effect of atomic beam alignment on photon correlation measurements in
cavity QED
Authors: L. Horvath and H. J. Carmichael
Categories: quant-ph
Comments: 15 pages and 13 figures
\\
Quantum trajectory simulations of a cavity QED system comprising an atomic
beam traversing a standing-wave cavity are carried out. The delayed photon
coincident rate for forwards scattering is computed and compared with the
measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et
al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that a moderate atomic beam
misalignment can account for the degradation of the predicted correlation. Fits
to the experimental data are made in the weak-field limit with a single
adjustable parameter--the atomic beam tilt from perpendicular to the cavity
axis. Departures of the measurement conditions from the weak-field limit are
discussed.
\\ ( http://arxiv.org/abs/0704.1686 , 757kb)
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arXiv:0704.1881
Date: Sat, 14 Apr 2007 16:43:25 GMT (354kb)

Title: Statistical Properties of Many Particle Eigenfunctions
Authors: Eric J. Heller and Brian R. Landry
Categories: quant-ph
\\
Wavefunction correlations and density matrices for few or many particles are
derived from the properties of semiclassical energy Green functions. Universal
features of fixed energy (microcanonical) random wavefunction correlation
functions appear which reflect the emergence of the canonical ensemble as the
number of particles approaches infinity. This arises through a little known
asymptotic limit of Bessel functions. Constraints due to symmetries,
boundaries, and collisions between particles can be included.
\\ ( http://arxiv.org/abs/0704.1881 , 354kb)
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arXiv:0704.1896
Date: Sun, 15 Apr 2007 07:26:51 GMT (31kb)

Title: Path Distinguishability in Double Scattering of Light by Atoms
Authors: Christian Miniatura, Cord A. M\"uller, Yin Lu, Guangquan Wang,
Berthold-Georg Englert
Categories: quant-ph
\\
Wave-particle duality finds a natural application for electrons or light
propagating in disordered media where coherent corrections to transport are
given by two-wave interference. For scatterers with internal degrees of
freedom, these corrections are observed to be much smaller than would be
expected for structureless scatterers. By examining the basic example of the
scattering of one photon by two spin-1/2 atoms--a case-study for coherent
backscattering--we demonstrate that the loss of interference strength is
associated with which-path information stored by the scattering atoms.
\\ ( http://arxiv.org/abs/0704.1896 , 31kb)
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arXiv:0704.1880
Date: Mon, 16 Apr 2007 15:34:49 GMT (54kb)

Title: Quantum Quenches in Extended Systems
Authors: Pasquale Calabrese, John Cardy
Categories: cond-mat.stat-mech
\\
We study in general the time-evolution of correlation functions in a extended
quantum system after the quench of a parameter in the hamiltonian. We show that
correlation functions in d dimensions can be extracted using methods of
boundary critical phenomena in d+1 dimensions. For d=1 this allows to use the
powerful tools of conformal field theory in the case of critical evolution.
Several results are obtained in generic dimension in the gaussian (mean-field)
approximation. These predictions are checked against the real-time evolution of
some solvable models that allows also to understand which features are valid
beyond the critical evolution.
All our findings may be explained in terms of a picture generally valid,
whereby quasiparticles, entangled over regions of the order of the correlation
length in the initial state, then propagate with a finite speed through the
system. Furthermore we show that the long-time results can be interpreted in
terms of a generalized Gibbs ensemble. We discuss some open questions and
possible future developments.
\\ ( http://arxiv.org/abs/0704.1880 , 54kb)
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arXiv:0704.1889
Date: Sun, 15 Apr 2007 00:02:39 GMT (41kb)

Title: First and second sound modes at finite temperature in trapped Fermi
gases from BCS to BEC
Authors: Yan He, Qijin Chen, Chih-Chun Chien, and K. Levin
Categories: cond-mat.str-el cond-mat.supr-con
\\
We determine the temperature $T$ dependence of first and second sound mode
frequencies for trapped Fermi gases undergoing BCS to Bose Einstein
condensation (BEC) crossover. Our results, based on the two fluid equations,
show that the lowest radial breathing mode is nearly $T$ independent as in
experiment, most strikingly at unitarity, but on the near-BCS and near-BEC
sides as well. At finite $T$, higher order breathing modes are predicted to
strongly mix with second sound. Their complex $T$ dependence should provide a
signature of superfluidity.
\\ ( http://arxiv.org/abs/0704.1889 , 41kb)
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arXiv:0704.1953
Date: Mon, 16 Apr 2007 09:04:32 GMT (157kb)

Title: Ramsey fringes formation during excitation of topological modes in a
Bose-Einstein condensate
Authors: E.R.F. Ramos, L. Sanz, V.I. Yukalov, and V.S. Bagnato
Categories: cond-mat.stat-mech cond-mat.mes-hall
Comments: Latex file, 12 pages, 5 figures
Journal-ref: Phys. Lett. A 365 (2007) 126-130
\\
The Ramsey fringes formation during the excitation of topological coherent
modes of a Bose-Einstein condensate by an external modulating field is
considered. The Ramsey fringes appear when a series of pulses of the excitation
field is applied. In both Rabi and Ramsey interrogations, there is a shift of
the population maximum transfer due to the strong non-linearity present in the
system. It is found that the Ramsey pattern itself retains information about
the accumulated relative phase between both ground and excited coherent modes.
\\ ( http://arxiv.org/abs/0704.1953 , 157kb)
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arXiv:0704.1971
Date: Mon, 16 Apr 2007 10:05:11 GMT (189kb)

Title: Dissipative dynamics of superfluid vortices at non-zero temperatures
Authors: Natalia G. Berloff and Anthony J. Youd
Categories: cond-mat.soft
\\
We consider the evolution and dissipation of vortex rings in a condensate at
non-zero temperature, in the context of the classical field approximation,
based on the defocusing nonlinear Schr\"odinger equation. The temperature in
such a system is fully determined by the total number density and the number
density of the condensate. A vortex ring is introduced into a condensate in a
state of thermal equilibrium, and interacts with non-condensed particles. These
interactions lead to a gradual decrease in the vortex line density, until the
vortex ring completely disappears. We show that the square of the vortex line
density changes linearly with time, and obtain the corresponding universal
decay law, which gives an exponential dependence on temperature.
\\ ( http://arxiv.org/abs/0704.1971 , 189kb)
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arXiv:0704.1995
Date: Mon, 16 Apr 2007 12:19:13 GMT (85kb)

Title: Coherent dynamics of domain formation in the Bose Ferromagnet
Authors: Qiang Gu, Haibo Qiu, Kai Bongs, Klaus Sengstock
Categories: cond-mat.other cond-mat.stat-mech
Comments: 4 pages, 3 figures, Accepted for publishing in PRL
\\
We present a theory to describe domain formation observed very recently in a
quenched Rb-87 gas, a typical ferromagnetic spinor Bose system. An overlap
factor is introduced to characterize the symmetry breaking of M_F=\pm 1
components for the F=1 ferromagnetic condensate. We demonstrate that the domain
formation is a co-effect of the quantum coherence and the thermal relaxation. A
thermally enhanced quantum-oscillation is observed during the dynamical process
of the domain formation. And the spatial separation of domains leads to
significant decay of the M_F=0 component fraction in an initial M_F=0
condensate.
\\ ( http://arxiv.org/abs/0704.1995 , 85kb)
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arXiv:0704.2054
Date: Sun, 15 Apr 2007 21:39:23 GMT (1197kb,D)

Title: Vortex Formation by Merging and Interference of Multiple Trapped
Bose-Einstein Condensates
Authors: David R. Scherer
Categories: cond-mat.other
Comments: Ph.D. dissertation submitted to the University of Arizona, 178 pages
including 53 heavily compressed images; high resolution version is available
at http://www.optics.arizona.edu/Anderson/
\\
An apparatus for producing atomic-gas Bose-Einstein condensates (BECs) of
87-Rb atoms is described. The apparatus produces 87-Rb BECs in a dual-chamber
vacuum system that incorporates magnetic transport of trapped atoms from the
magneto-optical trapping cell to the BEC production cell via the operation of a
series of overlapping magnet coils. The design, construction, and operation of
the apparatus are described in detail. The apparatus is used to study the
creation of quantized vortices in BECs by the merging and interference of
multiple trapped condensates. In this experiment, a single harmonic potential
well is partitioned into three sections by an optical barrier, enabling the
simultaneous formation of three independent, uncorrelated BECs. The BECs may
either merge together during their growth, or, for high-energy barriers, the
BECs can be merged together by barrier removal after their formation. Either
process may instigate vortex formation in the resulting BEC, depending on the
initially indeterminate relative phases of the condensates and the merging
rate.
\\ ( http://arxiv.org/abs/0704.2054 , 1197kb)
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arXiv:0704.1974
Date: Mon, 16 Apr 2007 10:36:55 GMT (225kb)

Title: Agile low phase noise radio-frequency sine wave generator applied to
experiments on ultracold atoms
Authors: Olivier Morizot (LPL), Julien De Lapeyre De Bellair (LPL), Fabrice
Wiotte (LPL), Olivier Lopez (LPL), Paul-Eric Pottie (LPL), H\'el\ene Perrin
(LPL)
Categories: physics.atom-ph
Proxy: ccsd hal-00141806
\\
We report on the frequency performance of a low cost (~500$) radio-frequency sine wave generator, using direct digital synthesis (DDS) and a field-programmable gate array (FPGA). The output frequency of the device may be changed dynamically to any arbitrary value ranging from DC to 10 MHz without any phase slip. Sampling effects are substantially reduced by a high sample rate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. By using a low noise external oscillator to clock the DDS, we demonstrate a phase noise as low as that of the master clock, that is at the level of -113 dB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. The device is successfully used to confine an ultracold atomic cloud of rubidium 87 in a RF-based trap, and there is no extra heating from the RF source. \\ ( http://arxiv.org/abs/0704.1974 , 225kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2082 Date: Tue, 17 Apr 2007 00:51:01 GMT (235kb) Title: Direct measurement of quantum phase gradients in superfluid 4He flow Authors: Yuki Sato, Aditya Joshi, and Richard Packard Categories: cond-mat.supr-con \\ We report a new kind of experiment in which we generate a known superfluid velocity in a straight tube and directly determine the phase difference across the tube's ends using a superfluid matter wave interferometer. By so doing, we quantitatively verify the relation between the superfluid velocity and the phase gradient of the condensate macroscopic wave function. Within the systematic error of the measurement (~10%) we find v_s=(hbar/m_4)*(grad phi). \\ ( http://arxiv.org/abs/0704.2082 , 235kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2155 Date: Tue, 17 Apr 2007 13:58:51 GMT (65kb) Title: Atom-molecule Rabi oscillations in a Mott insulator Authors: N. Syassen, D. M. Bauer, M. Lettner, D. Dietze, T. Volz, S. D\"urr, and G. Rempe Categories: cond-mat.stat-mech \\ We observe large-amplitude Rabi oscillations between an atomic and a molecular state near a Feshbach resonance. The experiment uses 87Rb in an optical lattice and a Feshbach resonance near 414 G. The frequency and amplitude of the oscillations depend on magnetic field in a way that is well described by a two-level model. The observed density dependence of the oscillation frequency agrees with the theoretical expectation. We confirmed that the state produced after a half-cycle contains exactly one molecule at each lattice site. In addition, we show that for energies in a gap of the lattice band structure, the molecules cannot dissociate. \\ ( http://arxiv.org/abs/0704.2155 , 65kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2097 Date: Tue, 17 Apr 2007 05:08:46 GMT (430kb) Title: Effects of Measurement back-action in the stabilization of a Bose-Einstein condensate through feedback Authors: S.D.Wilson, A.R.R.Carvalho, J.J.Hope and M.R.James Categories: quant-ph Comments: 1 Tex, 4 PS pictures, 1 bbl file \\ We apply quantum filtering and control to a particle in a harmonic trap under continuous position measurement, and show that a simple static feedback law can be used to cool the system. The final steady state is Gaussian and dependent on the feedback strength and coupling between the system and probe. In the limit of weak coupling this final state becomes the ground state. An earlier model by Haine et. al. (PRA 69, 2004) without measurement back-action showed dark states: states that did not display error signals, thus remaining unaffected by the control. This paper shows that for a realistic measurement process this is not true, which indicates that a Bose-Einstein condensate may be driven towards the ground state from any arbitrary initial state. \\ ( http://arxiv.org/abs/0704.2097 , 430kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2194 Date: Tue, 17 Apr 2007 16:43:30 GMT (6kb) Title: Casimir Friction I: Friction of vacuum on spinning dielectric Authors: Yves Pomeau and David C. Roberts Categories: quant-ph Comments: campanion article to cond-mat/0503757 \\ We introduce the concept of Casimir friction, i.e. friction due to quantum fluctuations. In this first article we describe the calculation of a constant torque, arising from the scattering of quantum fluctuations, on a dielectric rotating in an electromagnetic vacuum. \\ ( http://arxiv.org/abs/0704.2194 , 6kb) ------------------------------------------------------------------------------ \\ arXiv:0704.1382 (*cross-listing*) Date: Wed, 11 Apr 2007 09:39:45 GMT (119kb) Title: Effects of atomic interactions on Quantum Accelerator Modes Authors: Laura Rebuzzini, Roberto Artuso, Shmuel Fishman and Italo Guarneri. Categories: nlin.CD quant-ph Comments: 4 pages, 6 figures \\ We consider the influence of the inclusion of interatomic interactions on the delta-kicked accelerator model. Our analysis concerns in particular quantum accelerator modes, namely quantum ballistic transport near quantal resonances. The atomic interaction is modelled by a Gross-Pitaevskii cubic nonlinearity, and we address both attractive (focusing) and repulsive (defocusing) cases. The most remarkable effect is enhancement or damping of the accelerator modes, depending on the sign of the nonlinear parameter. We provide arguments showing that the effect persists beyond mean-field description, and lies within the experimentally accessible parameter range. \\ ( http://arxiv.org/abs/0704.1382 , 119kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2151 Date: Tue, 17 Apr 2007 13:42:17 GMT (46kb) Title: Spectroscopy of atomic rubidium at 500 bar buffer gas pressure: approaching the thermal equilibrium of dressed atom-light states Authors: U. Vogl and M. Weitz Categories: physics.atom-ph Comments: 4 pages \\ We have recorded fluorescence spectra of the atomic rubidium D-lines in the presence of several hundreds of bars buffer gas pressure. With additional saturation broadening a spectral linewidth comparable to the thermal energy of the atoms in the heated gas cell is achieved. An intensity-dependent blue asymmetry of the spectra is observed, which becomes increasingly pronounced when extrapolating to infinitely high light intensity. We interpret our results as evidence for the dressed (coupled atom-light) states to approach thermal equilibrium. \\ ( http://arxiv.org/abs/0704.2151 , 46kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2310 Date: Wed, 18 Apr 2007 10:10:01 GMT (25kb) Title: Mesoscopic Fluctuations of the Pairing Gap Authors: H. Olofsson, S. \AA berg & P. Leboeuf Categories: cond-mat.supr-con Comments: 4 pages, 2 figures \\ Superfluidity and superconductivity are genuine many-body manifestations of quantum coherence. For finite-size systems the associated pairing gap fluctuates as a function of size or shape. We provide a parameter free theoretical description of pairing fluctuations in mesoscopic systems characterized by order/chaos dynamics. The theory accurately describes experimental observations of nuclear superfluidity (regular system), predicts universal fluctuations of superconductivity in small chaotic metallic grains, and provides a global analysis in ultracold Fermi gases. \\ ( http://arxiv.org/abs/0704.2310 , 25kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2373 Date: Wed, 18 Apr 2007 16:02:53 GMT (32kb) Title: Mixing-demixing transition and collapse of a vortex state in a quasi-two-dimensional boson-fermion mixture Authors: Sadhan K. Adhikari and Luca Salasnich Categories: cond-mat.other Comments: 9 pages, 11 figures \\ We investigate the mixing-demixing transition and the collapse in a quasi-two-dimensional degenerate boson-fermion mixture (DBFM) with a bosonic vortex. We solve numerically a quantum-hydrodynamic model based on a new density functional which accurately takes into account the dimensional crossover. It is demonstrated that with the increase of interspecies repulsion, a mixed state of DBFM could turn into a demixed state. The system collapses for interspecies attraction above a critical value which depends on the vortex quantum number. For interspecies attraction just below this critical limit there is almost complete mixing of boson and fermion components. Such mixed and demixed states of a DBFM could be experimentally realized by varying an external magnetic field near a boson-fermion Feshbach resonance, which will result in a continuous variation of interspecies interaction. \\ ( http://arxiv.org/abs/0704.2373 , 32kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2412 Date: Wed, 18 Apr 2007 19:46:10 GMT (152kb) Title: Giant viscosity enhancement in a spin-polarized Fermi liquid Authors: H. Akimoto, J. S. Xia, D. Candela, W. J. Mullin, E. D. Adams, and N. S. Sullivan Categories: cond-mat.other Comments: 4 pages, 4 figures \\ The viscosity is measured for a Fermi liquid, a dilute$^3$He-$^4$He mixture, under extremely high magnetic field/temperature conditions ($B \leq 14.8$T,$T
\geq 1.5$mK). The spin splitting energy$\mu B$is substantially greater than the Fermi energy$k_B T_F$; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for$T \ll T_F$. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a$t$-matrix formalism. \\ ( http://arxiv.org/abs/0704.2412 , 152kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2246 Date: Tue, 17 Apr 2007 22:19:57 GMT (186kb) Title: Towards experimental entanglement connection with atomic ensembles in the single excitation regime Authors: J. Laurat, C.W. Chou, H. Deng, K.S. Choi, D. Felinto, H. de Riedmatten, H.J. Kimble Categories: quant-ph \\ We present a protocol for performing entanglement connection between pairs of atomic ensembles in the single excitation regime. Two pairs are prepared in an asynchronous fashion and then connected via a Bell measurement. The resulting state of the two remaining ensembles is mapped to photonic modes and a reduced density matrix is then reconstructed. Our observations confirm for the first time the creation of coherence between atomic systems that never interacted, a first step towards entanglement connection, a critical requirement for quantum networking and long distance quantum communications. \\ ( http://arxiv.org/abs/0704.2246 , 186kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2299 Date: Wed, 18 Apr 2007 09:29:15 GMT (244kb) Title: One-dimensional quantum Rydberg gases in a magneto-electric trap Authors: Michael Mayle, Bernd Hezel, Igor Lesanovsky and Peter Schmelcher Categories: physics.atom-ph \\ We study the quantum properties of Rydberg atoms in a magnetic Ioffe-Pritchard trap which is superimposed by a homogeneous electric field. Trapped Rydberg atoms can be created in long-lived electronic states exhibiting a permanent electric dipole moment of several hundred Debye. The resulting dipole-dipole interaction in conjunction with the radial confinement is demonstrated to give rise to an effectively one-dimensional ultracold quantum Rydberg gas with a macroscopic interparticle distance. We derive analytical expressions for the electric dipole moment and the critical linear density of Rydberg atoms. \\ ( http://arxiv.org/abs/0704.2299 , 244kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2427 Date: Wed, 18 Apr 2007 20:39:12 GMT (754kb) Title: Stationary and non-stationary fluid flow of a Bose-Einstein condensate through a penetrable barrier Authors: P. Engels and C. Atherton Categories: cond-mat.other Comments: 4 pages, 4 figures \\ We experimentally study the fluid flow induced by a broad, penetrable barrier moving through an elongated dilute gaseous Bose-Einstein condensate. The barrier is created by a laser beam swept through the condensate, and the resulting dipole potential can be either attractive or repulsive. We examine both cases and find regimes of stable and unstable fluid flow: At slow speeds of the barrier, the fluid flow is stationary due to the superfluidity of the condensate. At intermediate speeds, we observe a non-stationary regime in which the condensate gets filled with dark solitons. At faster speeds, soliton formation completely ceases and a remarkable absence of excitation in the condensate is seen again. \\ ( http://arxiv.org/abs/0704.2427 , 754kb) ------------------------------------------------------------------------------ \\ arXiv:0704.2431 Date: Wed, 18 Apr 2007 21:47:15 GMT (39kb,D) Title: Vortex trapping in suddenly connected Bose-Josephson junctions Authors: Parag Ghosh and Fernando Sols Categories: cond-mat.supr-con Comments: 4 pages, 5 figures \\ We investigate the problem of vortex trapping in cyclically coupled Bose-Josephson junctions. Starting with$N$independent BECs we couple the condensates through Josephson links and allow the system to reach a stable circulation by adding a dissipative term in our semiclassical equations of motion. The central question we address is what is the probability to trap a vortex with winding number$m$. Our numerical simulations reveal that the final distribution of winding numbers is narrower than the initial distribution of total phases, indicating an increased probability for no-vortex configurations. Further, the nonlinearity of the problem manifests itself in the somewhat counter-intuitive result that it is possible to obtain a non-zero circulation starting with zero total phase around the loop. The final width of the distribution of winding numbers for$N$sites scales as$\lambda N^{\alpha}$, where$\alpha=0.47\pm 0.01$and$\lambda <0.67$(value predicted for the initial distribution) indicating a shrinking of the final distribution. The actual value of$\lambda\$ is found to depend on the strength of dissipation.
\\ ( http://arxiv.org/abs/0704.2431 , 39kb)
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arXiv:0704.2439
Date: Thu, 19 Apr 2007 01:46:00 GMT (21kb)

Title: Quantum phase transitions beyond the dilute Bose gas limit
Authors: Valeri N. Kotov, D. X. Yao, A. H. Castro Neto, D. K. Campbell
Categories: cond-mat.str-el
\\
We study a Heisenberg S=1/2 ring-exchange antiferromagnet which exhibits a
quantum phase transition from a spontaneously dimerized (valence bond solid)
phase to a magnetically ordered (Neel) phase. We argue that the quantum
transition is of unconventional nature; both singlet and triplet modes of high
density condense as the transition is approached from the dimer side, signaling
restoration of lattice symmetry. These features are consistent with "deconfined
quantum criticality", of which the present model is believed to be the only
example so far.
\\ ( http://arxiv.org/abs/0704.2439 , 21kb)
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arXiv:0704.2496
Date: Thu, 19 Apr 2007 10:18:35 GMT (452kb)

Title: Phase Boundary of the Boson Mott Insulator in a Rotating Optical Lattice
Authors: R. O. Umucalilar, M. O. Oktel
Categories: cond-mat.mes-hall
Comments: 5 pages,3 figures. High resolution figures available upon request
\\
We consider the Bose-Hubbard model in a two dimensional rotating optical
lattice and investigate the consequences of the effective magnetic field
created by rotation. Using a Gutzwiller type variational wavefunction, we find
an analytical expression for the Mott insulator(MI)-Superfluid(SF) transition
boundary in terms of the maximum eigenvalue of the Hofstadter butterfly. The
dependence of phase boundary on the effective magnetic field is complex,
reflecting the self-similar properties of the single particle energy spectrum.
Finally, we argue that fractional quantum Hall phases exist close to the MI-SF
transition boundaries, including MI states with particle densities greater than
one.
\\ ( http://arxiv.org/abs/0704.2496 , 452kb)
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arXiv:0704.2280 (*cross-listing*)
Date: Wed, 18 Apr 2007 07:11:33 GMT (198kb)

Title: Full-time dynamics of modulational instability in spinor Bose--Einstein
condensates
Authors: Evgeny V. Doktorov, Vassilis M. Rothos, Yuri S. Kivshar
Categories: nlin.SI cond-mat.other
Comments: 6 pages, 2 figures, submitted to Phys. Rev. A
\\
We describe the full-time dynamics of modulational instability in spinor
Bose-Einstein condensates for the case of the integrable three-component model
associated with the matrix nonlinear Schroedinger equation. We obtain exact
homoclinic solution of this model by the dressing method generalized to the
case of higher-rank projectors. It is the homoclinic solution that is concerned
with the modulational instability development beyond the linear regime. We show
that the modulational instability demonstrates the reversal property when the
growth of the modulation amplitude changes by its exponential decay.
\\ ( http://arxiv.org/abs/0704.2280 , 198kb)
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arXiv:0704.2425
Date: Wed, 18 Apr 2007 20:29:27 GMT (88kb)

Title: Trapping and Cooling a mirror to its quantum mechanical ground state
Authors: M. Bhattacharya and P. Meystre
Categories: quant-ph
\\
We propose a technique aimed at cooling a harmonically oscillating mirror to
its quantum mechanical ground state starting from room temperature. Our method,
which involves the two-sided irradiation of the vibrating mirror inside an
optical cavity, combines several advantages over the two-mirror arrangements
being used currently. For comparable parameters the three-mirror configuration
provides a stiffer trap for the oscillating mirror. Furthermore it prevents
bistability from limiting the use of higher laser powers for mirror trapping,
and also partially does so for mirror cooling. Lastly, it improves the
isolation of the mirror from classical noise so that its dynamics are perturbed
mostly by the vacuum fluctuations of the optical fields. These improvements are
expected to bring the task of achieving ground state occupation for the mirror
closer to completion.
\\ ( http://arxiv.org/abs/0704.2425 , 88kb)
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arXiv:0704.1644 (*cross-listing*)
Date: Thu, 12 Apr 2007 18:55:27 GMT (164kb)

Title: Circulating Current States in Bilayer Fermionic and Bosonic Systems
Authors: Alexei Kolezhuk
Categories: cond-mat.other physics.atom-ph quant-ph
\\
It is shown that fermionic polar molecules or atoms in a bilayer optical
lattice can undergo the transition to a state with circulating currents, which
spontaneously breaks the time reversal symmetry. Estimates of relevant
temperature scales are given and experimental signatures of the circulating
current phase are identified. Related phenomena in bosonic and spin systems
with ring exchange are discussed.
\\ ( http://arxiv.org/abs/0704.1644 , 164kb)
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The replacements:

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arXiv:0704.0925
replaced with revised version Fri, 13 Apr 2007 14:58:49 GMT (576kb)

Title: Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate
Authors: A.T. Black, E. Gomez, L.D. Turner, S. Jung, P.D. Lett
Categories: cond-mat.other cond-mat.soft cond-mat.stat-mech
\\ ( http://arxiv.org/abs/0704.0925 , 576kb)
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arXiv:cond-mat/0702315
replaced with revised version Mon, 16 Apr 2007 07:55:35 GMT (45kb)

Title: Interacting bosons in an optical lattice: Bose-Einstein condensates and
Mott insulator
Authors: O. Fialko, Ch. Moseley and K. Ziegler
Categories: cond-mat.stat-mech
\\ ( http://arxiv.org/abs/cond-mat/0702315 , 45kb)
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\\
arXiv:cond-mat/0702014 (*cross-listing*)
replaced with revised version Mon, 16 Apr 2007 08:53:27 GMT (102kb)

Title: Robustness of adiabatic passage trough a quantum phase transition
Authors: Andrea Fubini, Giuseppe Falci, and Andreas Osterloh
Categories: cond-mat.stat-mech cond-mat.mes-hall quant-ph
Comments: 16 pages, 15 figures. To appear in New Journal of Physics
\\ ( http://arxiv.org/abs/cond-mat/0702014 , 102kb)
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\\
arXiv:cond-mat/0602572
replaced with revised version Tue, 17 Apr 2007 01:24:16 GMT (177kb)

Title: Dynamical Instability of a Rotating Dipolar Bose-Einstein Condensate
Authors: R.M.W. van Bijnen, D.H.J. O'Dell, N.G. Parker and A.M. Martin
Categories: cond-mat.other
Comments: 4 pages, including 2 figures
Journal-ref: Phys. Rev. Lett. 98, 150401 (2007)
\\ ( http://arxiv.org/abs/cond-mat/0602572 , 177kb)
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\\
arXiv:quant-ph/0702039
replaced with revised version Tue, 17 Apr 2007 18:35:56 GMT (360kb,D)

Title: Sublattice addressing and spin-dependent motion of atoms in a
double-well lattice
Authors: P. J. Lee, M. Anderlini, B. L. Brown, J. Sebby-Strabley, W. D.
Phillips, J. V. Porto
Categories: quant-ph
\\ ( http://arxiv.org/abs/quant-ph/0702039 , 360kb)
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\\
arXiv:quant-ph/0702162
replaced with revised version Tue, 17 Apr 2007 19:54:11 GMT (524kb)

Title: Trapping and observing single atoms in the dark
Authors: T. Puppe, I. Schuster, A. Grothe, A. Kubanek, K. Murr, P.W.H. Pinkse,
and G. Rempe
Categories: quant-ph
\\ ( http://arxiv.org/abs/quant-ph/0702162 , 524kb)
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\\
arXiv:cond-mat/0503757
replaced with revised version Wed, 18 Apr 2007 00:04:53 GMT (8kb)

Title: Casimir Friction II: Casimir effect and drag in zero temperature
superfluids
Authors: D. C. Roberts and Y. Pomeau
Categories: cond-mat.stat-mech
Comments: v4: rewrote as companion article to arXiv:0704.2194
\\ ( http://arxiv.org/abs/cond-mat/0503757 , 8kb)
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\\
arXiv:hep-ph/0703042 (*cross-listing*)
replaced with revised version Wed, 18 Apr 2007 08:18:45 GMT (22kb)

Title: Relativistic BCS-BEC Crossover at Zero Temperature
Authors: Lianyi He and Pengfei Zhuang
Categories: hep-ph cond-mat.supr-con hep-th nucl-th
Comments: 8 pages, 3 figures. V2: typos corrected, a comment on mean field
\\ ( http://arxiv.org/abs/hep-ph/0703042 , 22kb)
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arXiv:cond-mat/0607138
replaced with revised version Thu, 19 Apr 2007 11:58:45 GMT (504kb)

Title: Color Superfluidity and "Baryon" Formation in Ultracold Fermions
Authors: Akos Rapp, Gergely Zarand, Carsten Honerkamp, Walter Hofstetter
Categories: cond-mat.str-el cond-mat.supr-con
Comments: 4 PRL pages, 1 figure
Journal-ref: Physical Review Letters 98, 160405 (2007)
DOI: 10.1103/PhysRevLett.98.160405
\\ ( http://arxiv.org/abs/cond-mat/0607138 , 504kb)
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arXiv:cond-mat/0607831
replaced with revised version Thu, 19 Apr 2007 14:19:51 GMT (487kb)

Title: Correlations in a BEC collision: First-principles quantum dynamics with
150 000 atoms
Authors: P. Deuar and P. D. Drummond
Categories: cond-mat.other
Comments: 4 pages, 4 figures. v2: Rewording and style changes, minor except for
rewrite of background on the positive-P representation. Original research
unchanged
Journal-ref: Phys. Rev. Lett. 98, 120402 (2007)
\\ ( http://arxiv.org/abs/cond-mat/0607831 , 487kb)
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Till next time (which hopefully will be sooner!)
Matt.

--
=========================================================================
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 Apr 27 2007 - 15:27:55 EST

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