57 research outputs found
Stochastic Mean-Field Theory for the Disordered Bose-Hubbard Model
We investigate the effect of diagonal disorder on bosons in an optical
lattice described by an Anderson-Hubbard model at zero temperature. It is known
that within Gutzwiller mean-field theory spatially resolved calculations suffer
particularly from finite system sizes in the disordered case, while arithmetic
averaging of the order parameter cannot describe the Bose glass phase for
finite hopping . Here we present and apply a new \emph{stochastic}
mean-field theory which captures localization due to disorder, includes
non-trivial dimensional effects beyond the mean-field scaling level and is
applicable in the thermodynamic limit. In contrast to fermionic systems, we
find the existence of a critical hopping strength, above which the system
remains superfluid for arbitrarily strong disorder.Comment: 6 pages, 6 figure
Equilibrium and Disorder-induced behavior in Quantum Light-Matter Systems
We analyze equilibrium properties of coupled-doped cavities described by the
Jaynes-Cummings- Hubbard Hamiltonian. In particular, we characterize the
entanglement of the system in relation to the insulating-superfluid phase
transition. We point out the existence of a crossover inside the superfluid
phase of the system when the excitations change from polaritonic to purely
photonic. Using an ensemble statistical approach for small systems and
stochastic-mean-field theory for large systems we analyze static disorder of
the characteristic parameters of the system and explore the ground state
induced statistics. We report on a variety of glassy phases deriving from the
hybrid statistics of the system. On-site strong disorder induces insulating
behavior through two different mechanisms. For disorder in the light-matter
detuning, low energy cavities dominate the statistics allowing the excitations
to localize and bunch in such cavities. In the case of disorder in the light-
matter coupling, sites with strong coupling between light and matter become
very significant, which enhances the Mott-like insulating behavior. Inter-site
(hopping) disorder induces fluidity and the dominant sites are strongly coupled
to each other.Comment: about 10 pages, 12 figure
Dynamics of cold bosons in optical lattices: Effects of higher Bloch bands
The extended effective multiorbital Bose-Hubbard-type Hamiltonian which takes
into account higher Bloch bands, is discussed for boson systems in optical
lattices, with emphasis on dynamical properties, in relation with current
experiments. It is shown that the renormalization of Hamiltonian parameters
depends on the dimension of the problem studied. Therefore, mean field phase
diagrams do not scale with the coordination number of the lattice. The effect
of Hamiltonian parameters renormalization on the dynamics in reduced
one-dimensional optical lattice potential is analyzed. We study both the
quasi-adiabatic quench through the superfluid-Mott insulator transition and the
absorption spectroscopy, that is energy absorption rate when the lattice depth
is periodically modulated.Comment: 23 corrected interesting pages, no Higgs boson insid
Rigorous mean-field dynamics of lattice bosons: Quenches from the Mott insulator
We provide a rigorous derivation of Gutzwiller mean-field dynamics for
lattice bosons, showing that it is exact on fully connected lattices. We apply
this formalism to quenches in the interaction parameter from the Mott insulator
to the superfluid state. Although within mean-field the Mott insulator is a
steady state, we show that a dynamical critical interaction exists, such
that for final interaction parameter the Mott insulator is
exponentially unstable towards emerging long-range superfluid order, whereas
for the Mott insulating state is stable. We discuss the implications
of this prediction for finite-dimensional systems.Comment: 6 pages, 3 figures, published versio
Critical temperature of non-interacting Bose gases on disordered lattices
For a non-interacting Bose gas on a lattice we compute the shift of the
critical temperature for condensation when random-bond and onsite disorder are
present. We evidence that the shift depends on the space dimensionality D and
the filling fraction f. For D -> infinity (infinite-range model), using results
from the theory of random matrices, we show that the shift of the critical
temperature is negative, depends on f, and vanishes only for large f. The
connections with analogous results obtained for the spherical model are
discussed. For D=3 we find that, for large f, the critical temperature Tc is
enhanced by disorder and that the relative shift does not sensibly depend on f;
at variance, for small f, Tc decreases in agreement with the results obtained
for a Bose gas in the continuum. We also provide numerical estimates for the
shift of the critical temperature due to disorder induced on a non-interacting
Bose gas by a bichromatic incommensurate potential.Comment: 18 pages, 8 figures; Fig. 8 improved adding results for another value
of q (q=830/1076
Multi-orbital and density-induced tunneling of bosons in optical lattices
We show that multi-orbital and density-induced tunneling have a significant
impact on the phase diagram of bosonic atoms in optical lattices. Off-site
interactions lead to density-induced hopping, the so-called bond-charge
interactions, which can be identified with an effective tunneling potential and
can reach the same order of magnitude as conventional tunneling. In addition,
interaction-induced higher-band processes also give rise to strongly modified
tunneling, on-site and bond-charge interactions. We derive an extended
occupation-dependent Hubbard model with multi-orbitally renormalized processes
and compute the corresponding phase diagram. It substantially deviates from the
single-band Bose-Hubbard model and predicts strong changes of the superfluid to
Mott-insulator transition. In general, the presented beyond-Hubbard physics
plays an essential role in bosonic lattice systems and has an observable
influence on experiments with tunable interactions.Comment: 21 pages, 7 figure
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