1,871 research outputs found
Supersolid and pair correlations of the extended Jaynes-Cummings-Hubbard model on triangular lattices
We study the extended Jaynes-Cummings-Hubbard model on triangular cavity
lattices and zigzag ladders. By using density-matrix renormalization group
methods, we observe various types of solids with different density patterns and
find evidence for light supersolids, which exist in extended regions of the
phase diagram of the zigzag ladder. Furthermore, we observe strong pair
correlations in the supersolid phase due to the interplay between the atoms in
the cavities and atom-photon interaction. By means of cluster mean-field
simulations and a scaling of the cluster size extending our analysis to
two-dimensional triangular lattices, we present evidence for the emergence of a
light supersolid in this case also.Comment: 11 pages, 16 figure
Ultracold quantum gases in triangular optical lattices
Over the last years the exciting developments in the field of ultracold atoms
confined in optical lattices have led to numerous theoretical proposals devoted
to the quantum simulation of problems e.g. known from condensed matter physics.
Many of those ideas demand for experimental environments with non-cubic lattice
geometries. In this paper we report on the implementation of a versatile
three-beam lattice allowing for the generation of triangular as well as
hexagonal optical lattices. As an important step the superfluid-Mott insulator
(SF-MI) quantum phase transition has been observed and investigated in detail
in this lattice geometry for the first time. In addition to this we study the
physics of spinor Bose-Einstein condensates (BEC) in the presence of the
triangular optical lattice potential, especially spin changing dynamics across
the SF-MI transition. Our results suggest that below the SF-MI phase
transition, a well-established mean-field model describes the observed data
when renormalizing the spin-dependent interaction. Interestingly this opens new
perspectives for a lattice driven tuning of a spin dynamics resonance occurring
through the interplay of quadratic Zeeman effect and spin-dependent
interaction. We finally discuss further lattice configurations which can be
realized with our setup.Comment: 19 pages, 7 figure
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Quantum crystal growing: Adiabatic preparation of a bosonic antiferromagnet in the presence of a parabolic inhomogeneity
We theoretically study the adiabatic preparation of an antiferromagnetic
phase in a mixed Mott insulator of two bosonic atom species in a
one-dimensional optical lattice. In such a system one can engineer a tunable
parabolic inhomogeneity by controlling the difference of the trapping
potentials felt by the two species. Using numerical simulations we predict that
a finite parabolic potential can assist the adiabatic preparation of the
antiferromagnet. The optimal strength of the parabolic inhomogeneity depends
sensitively on the number imbalance between the two species. We also find that
during the preparation finite size effects will play a crucial role for a
system of realistic size. The experiment that we propose can be realized, for
example, using atomic mixtures of Rubidium 87 with Potassium 41 or Ytterbium
168 with Ytterbium 174.Comment: 25 pages, 6 figure
Topological Quantum Glassiness
Quantum tunneling often allows pathways to relaxation past energy barriers
which are otherwise hard to overcome classically at low temperatures. However,
this is not always the case. In this paper we provide simple exactly solvable
examples where the barriers each system encounters on its approach to lower and
lower energy states become increasingly large and eventually scale with the
system size. If the environment couples locally to the physical degrees of
freedom in the system, tunnelling under large barriers requires processes whose
order in perturbation theory is proportional to the width of the barrier. This
results in quantum relaxation rates that are exponentially suppressed in system
size: For these quantum systems, no physical bath can provide a mechanism for
relaxation that is not dynamically arrested at low temperatures. The examples
discussed here are drawn from three dimensional generalizations of Kitaev's
toric code, originally devised in the context of topological quantum computing.
They are devoid of any local order parameters or symmetry breaking and are thus
examples of topological quantum glasses. We construct systems that have slow
dynamics similar to either strong or fragile glasses. The example with
fragile-like relaxation is interesting in that the topological defects are
neither open strings or regular open membranes, but fractal objects with
dimension .Comment: (18 pages, 4 figures, v2: typos and updated figure); Philosophical
Magazine (2011
Vacancy diffusion in the triangular lattice dimer model
We study vacancy diffusion on the classical triangular lattice dimer model,
sub ject to the kinetic constraint that dimers can only translate, but not
rotate. A single vacancy, i.e. a monomer, in an otherwise fully packed lattice,
is always localized in a tree-like structure. The distribution of tree sizes is
asymptotically exponential and has an average of 8.16 \pm 0.01 sites. A
connected pair of monomers has a finite probability of being delocalized. When
delocalized, the diffusion of monomers is anomalous:Comment: 15 pages, 27 eps figures. submitted to Physical Review
Atomic quantum gases in periodically driven optical lattices
Time periodic forcing in the form of coherent radiation is a standard tool
for the coherent manipulation of small quantum systems like single atoms. In
the last years, periodic driving has more and more also been considered as a
means for the coherent control of many-body systems. In particular, experiments
with ultracold quantum gases in optical lattices subjected to periodic driving
in the lower kilohertz regime have attracted a lot of attention. Milestones
include the observation of dynamic localization, the dynamic control of the
quantum phase transition between a bosonic superfluid and a Mott insulator, as
well as the dynamic creation of strong artificial magnetic fields and
topological band structures. This article reviews these recent experiments and
their theoretical description. Moreover, fundamental properties of periodically
driven many-body systems are discussed within the framework of Floquet theory,
including heating, relaxation dynamics, anomalous topological edge states, and
the response to slow parameter variations.Comment: Review, accepted for publication as Colloquium in Reviews of Modern
Physic
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