676 research outputs found
Ultracold atoms in optical lattices
Bosonic atoms trapped in an optical lattice at very low temperatures, can be
modeled by the Bose-Hubbard model. In this paper, we propose a slave-boson
approach for dealing with the Bose-Hubbard model, which enables us to
analytically describe the physics of this model at nonzero temperatures. With
our approach the phase diagram for this model at nonzero temperatures can be
quantified.Comment: 29 pages, 10 figure
Quantum phases in a resonantly-interacting Bose-Fermi mixture
We consider a resonantly-interacting Bose-Fermi mixture of K and
Rb atoms in an optical lattice. We show that by using a red-detuned
optical lattice the mixture can be accurately described by a generalized
Hubbard model for K and Rb atoms, and K-Rb
molecules. The microscopic parameters of this model are fully determined by the
details of the optical lattice and the interspecies Feshbach resonance in the
absence of the lattice. We predict a quantum phase transition to occur in this
system already at low atomic filling fraction, and present the phase diagram as
a function of the temperature and the applied magnetic field.Comment: 4 pages, 3 figure
Coexistence of superfluid and Mott phases of lattice bosons
Recent experiments on strongly-interacting bosons in optical lattices have
revealed the co-existence of spatially-separated Mott-insulating and
number-fluctuating phases. The description of this inhomogeneous situation is
the topic of this Letter. We establish that the number-fluctuating phase forms
a superfluid trapped between the Mott-insulating regions and derive the
associated collective mode structure. We discuss the interlayer's crossover
between two- and three-dimensional behavior as a function of the lattice
parameters and estimate the critical temperatures for the transition of the
superfluid phase to a normal phase
Theory for Bose-Einstein condensation of light in nano-fabricated semiconductor microcavities
We construct a theory for Bose-Einstein condensation of light in
nano-fabricated semiconductor microcavities. We model the semiconductor by one
conduction and one valence band which consist of electrons and holes that
interact via a Coulomb interaction. Moreover, we incorporate screening effects
by using a contact interaction with the scattering length for a Yukawa
potential and describe in this manner the crossover from exciton gas to
electron-hole plasma as we increase the excitation level of the semiconductor.
We then show that the dynamics of the light in the microcavities is damped due
to the coupling to the semiconductor. Furthermore, we demonstrate that on the
electron-hole plasma side of the crossover, which is relevant for the
Bose-Einstein condensation of light, this damping can be described by a single
dimensionless damping parameter that depends on the external pumping.
Hereafter, we propose to probe the superfluidity of light in these
nano-fabricated semiconductor microcavities by making use of the differences in
the response in the normal or superfluid phase to a sudden rotation of the
trap. In particular, we determine frequencies and damping of the scissors modes
that are excited in this manner. Moreover, we show that a distinct signature of
the dynamical Casimir effect can be observed in the density-density
correlations of the excited light fluid
Mott insulators in an optical lattice with high filling factors
We discuss the superfluid to Mott insulator transition of an atomic Bose gas
in an optical lattice with high filling factors. We show that also in this
multi-band situation, the long-wavelength physics is described by a single-band
Bose-Hubbard model. We determine the many-body renormalization of the tunneling
and interaction parameters in the effective Bose-Hubbard Hamiltonian, and
consider the resulting model at nonzero temperatures. We show that in
particular for a one or two-dimensional optical lattice, the Mott insulator
phase is more difficult to realize than anticipated previously.Comment: 5 pages, 3 figures, title changed, major restructuring, resubmitted
to PR
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