Matt's arXiv selection: week ending 2 January 2009

From: Matthew Davis <>
Date: Fri, 27 Feb 2009 07:52:34 +1000

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

Hello all,

There were 21 new preprints and just a single replacement.

Date: Tue, 30 Dec 2008 20:15:08 GMT (130kb)

Title: The Higgs resonance in fermionic pairing
Authors: Roman Barankov
Categories: cond-mat.supr-con cond-mat.str-el
Comments: 4 pages, 2 figures
   The Higgs boson in fermionic condensates with the BCS pairing interaction
describes the dynamics of the pairing amplitude. I show that the existence and
properties of this mode are sensitive to the energy dispersion of the
interaction. Specifically, when the pairing is suppressed at the Fermi level,
the Higgs mode may become unphysical (virtual) state or a resonance with finite
lifetime, depending on the details of interaction. Conversely, the Higgs mode
is discrete for the pairing interaction enhanced at the Fermi level. This work
illustrates conceptual difficulties associated with introducing collective
variables in the many-body pairing dynamics.
\\ ( , 130kb)
Date: Thu, 25 Dec 2008 09:45:22 GMT (15kb)

Title: A theory of topological edges and domain walls
Authors: F.A. Bais, J.K. Slingerland, S.M. Haaker
Categories: cond-mat.mes-hall cond-mat.str-el
Comments: 4 pages, 1 figure, latex
Report-no: ITFA 2008-52
   We investigate domain walls between topologically ordered phases in two
spatial dimensions and present a simple but general framework from which their
degrees of freedom can be understood. The approach we present exploits the
results on topological symmetry breaking that we have introduced and presented
elsewhere. After summarizing the method, we work out predictions for the
spectrum of edge excitations and for the transport through edges in some
representative examples. These include domain walls between the Abelian and
non-Abelian topological phases of Kitaev's honeycomb lattice model in a
magnetic field, as well as recently proposed domain walls between spin
polarized and unpolarized non-Abelian fractional quantum Hall states at
different filling fractions.
\\ ( , 15kb)
Date: Thu, 25 Dec 2008 12:19:14 GMT (1044kb)

Title: Atomic Quantum Corrals for Bose-Einstein Condensates
Authors: Hongwei Xiong and Biao Wu
Categories: cond-mat.other
Comments: 4 pages, 5 figures
   A feasible scheme is proposed to build quantum corrals for Bose-Einstein
condensates. Compared to the electronic quantum corrals, the atomic quantum
corrals have the advantage of allowing direct and convenient observation of the
wave dynamics. Our numerical study shows that this advantage not only allows
people to explore the rich dynamical structures in the density distribution but
also makes the corrals useful in many other aspects. In particular, the corrals
for atoms can be arranged into a stadium shape for the experimental
visualization of quantum chaos, which has been elusive in the electronic
quantum corrals.
\\ ( , 1044kb)
Date: Thu, 25 Dec 2008 15:38:09 GMT (872kb)

Title: Gap-Townes solitons and delocalizing transitions of multidimensional
   Bose-Einstein condensates in optical lattices
Authors: M. Salerno, F. Kh. Abdullaev and B. B. Baizakov
Categories: cond-mat.other
Comments: 14 pages, 6 figures
   We show the existence of gap-Townes solitons for the multidimensional
Gross-Pitaeviskii equation with attractive interactions and in two- and
three-dimensional optical lattices. In absence of the periodic potential the
solution reduces to the known Townes solitons of the multi-dimensional
nonlinear Schr\"odinger equation, sharing with these the propriety of being
unstable against small norm (number of atoms) variations. We show that in the
presence of the optical lattice the solution separates stable localized
solutions (gap-solitons) from decaying ones, characterizing the delocalizing
transition occurring in the multidimensional case. The link between these
higher dimensional solutions and the ones of one dimensional nonlinear
Schr\"odinger equation with higher order nonlinearities is also discussed.
\\ ( , 872kb)
Date: Fri, 26 Dec 2008 22:19:41 GMT (959kb)

Title: Thermalization dynamics close to a quantum phase transition
Authors: Dario Patan\`e, Alessandro Silva, Fernando Sols, Luigi Amico
Categories: cond-mat.stat-mech
Comments: 4 pages, 4 figures
   We investigate the dissipative dynamics of a quantum critical system in
contact with a thermal bath. As a paradigmatic situation we focus on the
response of the system to a sudden change of the temperature of the bath. The
specific example of the XY model in a transverse magnetic field whose spins are
locally coupled to a set of bosonic baths is considered. The peculiar nature of
the dynamics is enclosed in the correlations which develop out of equilibrium.
By means of a kinetic equation we investigate the spin-spin correlation
function and also block correlations measured by quantum mutual information.
Two distinct regimes, characterized by different time and length scales, emerge
at short and long times. During the initial transient, despite being far from
equilibrium, the dynamics is characterized by the same critical exponents as
those of the equilibrium quantum phase transition. The equilibrium is
eventually reached through the propagation along the chain of a thermal front
whose speed is dictated by the final temperature and magnetic field.
\\ ( , 959kb)
Date: Sat, 27 Dec 2008 16:38:03 GMT (1138kb)

Title: Jordan-Wigner Fermionization and the Theory of Low-Dimensional Quantum
   Spin Models. Dynamic Properties
Authors: Oleg Derzhko
Categories: cond-mat.str-el cond-mat.stat-mech
Comments: 53 pages, 22 figures
   Phenomena, Materials, Ideas, Methods . Edited by Janusz Jedrzejewski (World
   Scientific, Singapore, 2008). P.35-87
   The Jordan-Wigner transformation is known as a powerful tool in condensed
matter theory, especially in the theory of low-dimensional quantum spin
systems. The aim of this chapter is to review the application of the
Jordan-Wigner fermionization technique for calculating dynamic quantities of
low-dimensional quantum spin models. After a brief introduction of the
Jordan-Wigner transformation for one-dimensional spin one-half systems and some
of its extensions for higher dimensions and higher spin values we focus on the
dynamic properties of several low-dimensional quantum spin models. We start
from the famous s=1/2 XX chain. As a first step we recall well-known results
for dynamics of the z-spin-component fluctuation operator and then turn to the
dynamics of the dimer and trimer fluctuation operators. The dynamics of the
trimer fluctuations involves both the two-fermion (one particle and one hole)
and the four-fermion (two particles and two holes) excitations. We discuss some
properties of the two-fermion and four-fermion excitation continua. The
four-fermion dynamic quantities are of intermediate complexity between simple
two-fermion (like the zz dynamic structure factor) and enormously complex
multi-fermion (like the xx or xy dynamic structure factors) dynamic quantities.
Further we discuss the effects of dimerization, anisotropy of XY interaction,
and additional Dzyaloshinskii-Moriya interaction on various dynamic quantities.
Finally we consider the dynamic transverse spin structure factor
$S_{zz}({\bf{k}},\omega)$ for the s=1/2 XX model on a spatially anisotropic
square lattice which allows one to trace a one-to-two-dimensional crossover in
dynamic quantities.
\\ ( , 1138kb)
Date: Sun, 28 Dec 2008 18:21:40 GMT (1403kb,D)

Title: Interference of interacting matter waves
Authors: Mattias Gustavsson, Elmar Haller, Manfred J. Mark, Johann G. Danzl,
   Russell Hart, Andrew J. Daley, Hanns-Christoph Naegerl
Categories: cond-mat.other
Comments: 5 figures
   The phenomenon of matter wave interference lies at the heart of quantum
physics. It has been observed in various contexts in the limit of
non-interacting particles as a single particle effect. Here we observe and
control matter wave interference whose evolution is driven by interparticle
interactions. In a multi-path matter wave interferometer, the macroscopic
many-body wave function of an interacting atomic Bose-Einstein condensate
develops a regular interference pattern, allowing us to detect and directly
visualize the effect of interaction-induced phase shifts. We demonstrate
control over the phase evolution by inhibiting interaction-induced dephasing
and by refocusing a dephased macroscopic matter wave in a spin-echo type
experiment. Our results show that interactions in a many-body system lead to a
surprisingly coherent evolution, possibly enabling narrow-band and
high-brightness matter wave interferometers based on atom lasers.
\\ ( , 1403kb)
Date: Sun, 28 Dec 2008 21:45:31 GMT (287kb)

Title: Bose-Einstein condensation of 2D dipolar excitons: Quantum Monte Carlo
Authors: Yu. E. Lozovik, I. L. Kurbakov, G. E. Astrakharchik, and M. Willander
Categories: cond-mat.str-el
Comments: 17 pages, 8 figures
Journal-ref: JETP 106(2), 296-315 (2008)
   The Bose condensation of 2D dipolar excitons in quantum wells is numerically
studied by the diffusion Monte Carlo simulation method. The correlation,
microscopic, thermodynamic, and spectral characteristics are calculated. It is
shown that, in structures of coupled quantum wells, in which low-temperature
features of exciton luminescence have presently been observed, dipolar excitons
form a strongly correlated system. Their Bose condensation can experimentally
be achieved much easily than for ideal or weakly correlated excitons.
\\ ( , 287kb)
Date: Sun, 28 Dec 2008 18:55:44 GMT (20kb)

Title: Electron-hole pair condensation in graphene bilayer
Authors: Yu.E. Lozovik, A.A. Sokolik
Categories: cond-mat.str-el
Comments: Submitted on November 26, 2007, Published on January 10, 2008.
   Several misprints in the in the original text are corrected
Journal-ref: Pis'ma v ZhETF, vol. 87, iss. 1, pp. 61-65 (2008);
   Translation:JETP Letters, vol. 87, No. 1, pp. 55-59 (2008)
   We consider the pairing of electrons and holes due to their Coulomb
attraction in two parallel, independently gated graphene layers, separated by a
barrier. At weak coupling, there exist the BCS-like pair-condensed state.
Despite the fact that electrons and holes behave like massless Dirac fermions,
the problem of BCS-like electron-hole pairing in graphene bilayer turns out to
be rather similar to that in usual coupled semiconductor quantum wells. The
distinctions are due to Berry phase of electronic wave functions and different
screening properties. We estimate values of the gap in one-particle excitation
spectrum for different interlayer distances and carrier concentrations.
Influence of disorder is discussed. At large enough dielectric susceptibility
of surrounding medium, the weak coupling regime holds even at arbitrarily small
carrier concentrations. Localized electron-hole pairs are absent in graphene,
thus the behavior of the system versus coupling strength is cardinally
different from usual BCS-BEC crossover.
\\ ( , 20kb)
Date: Mon, 29 Dec 2008 19:46:07 GMT (268kb)

Title: A Gross-Pitaevskii Treatment for Supersolid He
Authors: Philip W Anderson
Categories: cond-mat.stat-mech cond-mat.str-el
   The observations of non-linear rotational susceptibility (NCRI) in samples of
solid He below 1-200 mK temperatures are conjectured to be describable in terms
of a rarified Gross-Pitaevskii superfluid of vacancies (or, more generally,
incommensuracies) with a transition temperature of about 50 mK, whose density
is locally enhanced by crystal imperfections. We argue that the observations
can be much affected by this density enhancement. We argue also that it is
likely that the ground state of every pure Bose solid is supersolid.
\\ ( , 268kb)
Date: Tue, 30 Dec 2008 08:12:08 GMT (98kb)

Title: Asymmetric Pairing in Two-Species Fermionic System in the Presence of
   Feshbach Resonance
Authors: Raka Dasgupta
Categories: cond-mat.supr-con cond-mat.other
Comments: 11 pages,5 figures
   We have studied asymmetric pairing in a two-species fermionic system in the
presence of Feshbach resonance, where the two types of fermions combine to form
a boson molecule. It is shown that depending on whether the bosonic chemical
potential has a greater (smaller) numerical value than the threshold energy of
the composite bose particles, the BCS gap and the critical temperature
decreases (increases). We have also obtained the stability criteria of the
Breached Pair phase for this system. Considering the BCS-BEC crossover picture,
we have identified the regime where these stability criteria are fulfilled.
\\ ( , 98kb)
Date: Tue, 30 Dec 2008 12:37:17 GMT (57kb)

Title: Quantum Phases of Long Range 1-D Bose-Hubbard Model: Field Theoretic and
   DMRG Study at Different Densities
Authors: Manoranjan Kumar, Sujit Sarkar and S. Ramasesha
Categories: cond-mat.stat-mech
Comments: 6 pages and 5 figures
   We use Abelian Bosonization and density matrix renormalization group method
to study the effect of density on quantum phases of long range 1-D Bose-Hubbard
model. We predict the existence of supersolid phase and also other quantum
phases for this system. We have analyzed the role of long range interaction
parameter on solitonic phase near half filling. We discuss the effect of
dimerization in nearest neighbor hopping and interaction terms on the plateau
phase at the half filling.
\\ ( , 57kb)
Date: Tue, 30 Dec 2008 14:13:26 GMT (503kb)

Title: Chaotic dynamics of a Bose-Einstein condensate coupled to a qubit
Authors: J. Martin, B. Georgeot, D. L. Shepelyansky
Categories: cond-mat.stat-mech quant-ph
Comments: 4 pages, 6 figures. Research done at
   We study numerically the coupling between a qubit and a Bose-Einstein
condensate (BEC) moving in a kicked optical lattice, using Gross-Pitaevskii
equation. In the regime where the BEC size is smaller than the lattice period,
the chaotic dynamics of the BEC is effectively controlled by the qubit state.
The feedback effects of the nonlinear chaotic BEC dynamics preserve the
coherence and purity of the qubit in the regime of strong BEC nonlinearity.
This gives an example of an exponentially sensitive control over a macroscopic
state by internal qubit states. At weak nonlinearity quantum chaos leads to
rapid dynamical decoherence of the qubit. The realization of such coupled
systems is within reach of current experimental techniques.
\\ ( , 503kb)
Date: Tue, 30 Dec 2008 14:18:44 GMT (724kb,D)

Title: Deeply bound ultracold molecules in an optical lattice
Authors: Johann G. Danzl, Manfred J. Mark, Elmar Haller, Mattias Gustavsson,
   Russell Hart, Andreas Liem, Holger Zellmer, Hanns-Christoph Naegerl
Categories: cond-mat.other
Comments: 12 pages, 4 figures, submitted to the Special Issue of New Journal of
   Physics on Cold and Ultracold Molecules
   We demonstrate efficient transfer of ultracold molecules into a deeply bound
rovibrational level of the singlet ground state potential in the presence of an
optical lattice. The overall molecule creation efficiency is 25%, and the
transfer efficiency to the rovibrational level |v=73,J=2> is above 80%. We find
that the molecules in |v=73,J=2> are trapped in the optical lattice, limited by
optical excitation by the lattice light. The molecule trapping time for a
lattice depth of 15 atomic recoil energies is about 20 ms. We determine the
trapping frequency by the lattice phase and amplitude modulation technique. It
will now be possible to transfer the molecules to the rovibrational ground
state |v=0,J=0> in the presence of the optical lattice.
\\ ( , 724kb)
Date: Tue, 30 Dec 2008 19:20:23 GMT (639kb)

Title: Resonant Landau-Zener tunneling and Rabi oscillations of matter wave
Authors: Yu. V. Bludov, V. V. Konotop, M. Salerno
Categories: cond-mat.other
Comments: Submitted to Phys. Rev. Lett
   The possibility of resonant tunneling and Rabi oscillations of soliton matter
waves in combined linear and nonlinear optical lattices (OLs) under the action
of an external time dependent periodic force, is first demonstrated. It is
shown that under suitable conditions these oscillations become long lived. By
switching off the external force at proper times it is possible to put the
state of the system either in a pure (stationary macroscopically populated) gap
soliton state or in an entangled state, i.e. a linear combination of two gap
solitons, with appreciably long life-time.
\\ ( , 639kb)
Date: Fri, 26 Dec 2008 15:35:47 GMT (165kb,D)

Title: Spatial multimode entanglement within one laser beam
Authors: J. Janousek, K. Wagner, J-F. Morizur, N. Treps, P. K. Lam, C. C. Harb,
   H-A. Bachor
Categories: quant-ph
Comments: 7 pages, 3 figures
   Optical entanglement is a key requirement for many quantum communication
protocols. Conventionally entanglement is formed between two distinct beams,
with the quantum correlations being measured at separate locations. We show
entanglement between the modes within one beam. Our technique is particularly
elegant and a major advance towards practical systems with minimum complexity.
We demonstrate three major experimental achievements: (i) only one source is
required to produce squeezed light in two orthogonal spatial modes, (ii) the
entanglement is formed through lenses and beam rotation, without the need of a
beam splitter and (iii) the quantum correlations are measured directly and
simultaneously using a multi pixel, quadrant detector.
\\ ( , 165kb)
Date: Sat, 27 Dec 2008 11:10:02 GMT (484kb)

Title: Multimode quantum properties of a self-imaging OPO: squeezed vacuum and
   EPR beams generation
Authors: L. Lopez (LKB - Jussieu), Beno\^it Chalopin (LKB - Jussieu), Arnaud
   Rivi\`ere De La Souch\`ere (LKB - Jussieu), Claude Fabre (LKB - Jussieu),
   Agn\`es Ma\^itre (LKB - Jussieu, INSP), Nicolas Treps (LKB - Jussieu)
Categories: quant-ph
   We investigate the spatial quantum properties of the light emitted by a
perfectly spatially degenerate optical parametric oscillator (self-imaging
OPO). We show that this device produces local squeezing for areas bigger than a
coherence are that depends on the crystal length and pump width. Furthermore,
it generates local EPR beams in the far field. We show, calculating the
eigenmodes of the system, that it is highly multimode for realistic
experimental parameters.
\\ ( , 484kb)
Date: Sat, 27 Dec 2008 16:11:47 GMT (403kb)

Title: Resonant Cascaded Down-Conversion
Authors: Christian Weedbrook, Ben Perrett, Karen V. Kheruntsyan, Peter D.
   Drummond, Raphael C. Pooser, Olivier Pfister
Categories: quant-ph
Comments: 7 pages, 13 figures
   We analyze an optical parametric oscillator (OPO) in which cascaded
down-conversion occurs inside a cavity resonant for all modes but the initial
pump. Due to the resonant cascade design, the OPO present two \chi^2 level
oscillation thresholds that are therefore remarkably lower than for a \chi^3
OPO. This is promising for reaching the regime of an effective third-order
nonlinearity well above both thresholds. Such a \chi^2 cascaded device also has
potential applications in frequency conversion to far infra-red regimes. But,
most importantly, it can generate novel multi-partite quantum correlations in
the output radiation, which represent a step beyond squeezed or entangled
light. The output can be highly non-Gaussian, and therefore not describable by
any semi-classical model.
\\ ( , 403kb)
Date: Mon, 29 Dec 2008 01:36:17 GMT (318kb)

Title: Polarization-based Light-Atom Quantum Interface with an All-optical Trap
Authors: Marco Koschorreck, Marcin Kubasik, Mario Napolitano, Sebasti\'an R. de
   Echaniz, Herbert Crepaz, J\"urgen Eschner, Eugene S. Polzik, Morgan W.
Categories: quant-ph
Comments: 8 pages, 4 figures
   We describe the implementation of a system for studying light-matter
interactions using an ensemble of $10^6$ cold rubidium 87 atoms, trapped in a
single-beam optical dipole trap. In this configuration the elongated shape of
the atomic cloud increases the strength of the collective light-atom coupling.
Trapping all-optically allows for long storage times in a low decoherence
environment. We are able to perform several thousands of measurements on one
atomic ensemble with little destruction. We report results on paramagnetic
Faraday rotations from a macroscopically polarized atomic ensemble. Our results
confirm that strong light-atom coupling is achievable in this system which
makes it attractive for single-pass quantum information protocols.
\\ ( , 318kb)
Date: Mon, 29 Dec 2008 11:21:33 GMT (119kb)

Title: Collective Rydberg excitations of an atomic gas confined in a ring
Authors: B. Olmos, R. Gonz\'alez-F\'erez, I. Lesanovsky
Categories: quant-ph
Comments: 10 pages, 11 figures
   We study the excitation dynamics of Rydberg atoms in a one-dimensional
lattice with periodic boundary conditions where the atomic Rydberg states are
resonantly excited from the electronic ground state. Our description of the
corresponding dynamics is numerically exact within the perfect blockade regime,
i.e. no two atoms in a given range can be excited. The time-evolution of the
mean Rydberg density, density-density correlations as well as entanglement
properties are analyzed in detail. We demonstrate that the short time dynamics
is universal and dominated by quantum phenomena, while for larger time the
characteristics of the lattice become important and the classical features
determine the dynamics. The results of the perfect blockade approach are
compared to the predictions of an effective Hamiltonian which includes the
interaction of two neighboring Rydberg atoms up to second order perturbation
\\ ( , 119kb)
Date: Mon, 29 Dec 2008 17:16:53 GMT (503kb)

Title: Stored light and EIT at high optical depths
Authors: M. Klein, Y. Xiao, M. Hohensee, D.F. Phillips, and R.L. Walsworth
Categories: quant-ph
Comments: 8 pages, 5 figures, submitted to Proc. SPIE. Version here is slightly
   modified, including a different title and a redone Fig. 5
   We report a preliminary experimental study of EIT and stored light in the
high optical depth regime. In particular, we characterize two ways to mitigate
radiation trapping, a decoherence mechanism at high atomic density: nitrogen as
buffer gas, and a long, narrow cell geometry. Initial results show the promise
of both approaches in minimizing radiation trapping, but also reveal problems
such as optical pumping into trapped end-states. We also observe distortion in
EIT lineshapes at high optical depth, a result of interference from four-wave
mixing. Experimental results are in good qualitative agreement with theoretical
\\ ( , 503kb)

The replacement:

replaced with revised version Mon, 29 Dec 2008 19:01:05 GMT (277kb)

Title: Metastable superfluidity of repulsive fermionic atoms in optical
Authors: Achim Rosch, David Rasch, Benedikt Binz, Matthias Vojta
Categories: cond-mat.other cond-mat.supr-con
Comments: 4 pages, 3 figs; (v2) final version as published
Journal-ref: Phys. Rev. Lett. 101, 265301 (2008)
DOI: 10.1103/PhysRevLett.101.265301
\\ ( , 277kb)

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,        
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 Fri May 01 2009 - 15:51:03 EST

This archive was generated by hypermail 2.2.0 : Fri May 01 2009 - 15:52:18 EST