2,566 research outputs found
Two-body problem in periodic potentials
We investigate the problem of two atoms interacting via a short range s-wave
potential in the presence of a deep optical lattice of arbitrary dimension .
Using a tight binding approach, we derive analytical results for the properties
of the bound state and the scattering amplitude. We show that the tunneling
through the barriers induces a dimensional crossover from a confined regime at
high energy to an anisotropic three dimensional regime at low energy. The
critical value of the scattering length needed to form a two-body bound state
shows a logaritmic dependence on the tunneling rate for D=1 and a power law for
. For the special case D=1, we also compare our analytical predictions
with exact numerics, finding remarkably good agreement
Lattice modulation spectroscopy of strongly interacting bosons in disordered and quasi-periodic optical lattices
We compute the absorption spectrum of strongly repulsive one-dimensional
bosons in a disordered or quasi-periodic optical lattice. At commensurate
filling, the particle-hole resonances of the Mott insulator are broadened as
the disorder strength is increased. In the non-commensurate case, mapping the
problem to the Anderson model allows us to study the Bose-glass phase.
Surprisingly we find that a perturbative treatment in both cases, weak and
strong disorder, gives a good description at all frequencies. In particular we
find that the infrared absorption rate in the thermodynamic limit is quadratic
in frequency. This result is unexpected, since for other quantities like the
conductivity in one dimensional systems, perturbation theory is only applicable
at high frequencies. We discuss applications to recent experiments on optical
lattice systems, and in particular the effect of the harmonic trap.Comment: 11 pages, 8 figure
Attractive Fermi gases with unequal spin populations in highly elongated traps
We investigate two-component attractive Fermi gases with imbalanced spin
populations in trapped one dimensional configurations. The ground state
properties are determined within local density approximation, starting from the
exact Bethe-ansatz equations for the homogeneous case. We predict that the
atoms are distributed according to a two-shell structure: a partially polarized
phase in the center of the trap and either a fully paired or a fully polarized
phase in the wings. The partially polarized core is expected to be a superfluid
of the FFLO type. The size of the cloud as well as the critical spin
polarization needed to suppress the fully paired shell, are calculated as a
function of the coupling strength.Comment: Final accepted versio
Sound propagation and oscillations of a superfluid Fermi gas in the presence of a 1D optical lattice
We develop the hydrodynamic theory of Fermi superfluids in the presence of a
periodic potential. The relevant parameters governing the propagation of sound
(compressibility and effective mass) are calculated in the weakly interacting
BCS limit. The conditions of stability of the superfluid motion with respect to
creation of elementary excitations are discussed.
We also evaluate the frequency of the center of mass oscillation when the
superfluid gas is additionally confined by a harmonic trap.Comment: Version accepted in Phys. Rev. A. It contains a discussion on the
dynamical instability of Fermi superfluids in optical lattice
In-Plane Conductivity Anisotropy in Underdoped Cuprates in the Spin-Charge Gauge Approach
Applying the recently developed spin-charge gauge theory for the pseudogap
phase in cuprates, we propose a self-consistent explanation of several peculiar
features of the far-infrared in-plane AC conductivity, including a broad peak
as a function of frequency and significant anisotropy at low temperatures,
along with a similar temperature-dependent in-plane anisotropy of DC
conductivity in lightly doped cuprates. The anisotropy of the metal-insulator
crossover scale is considered to be responsible for these phenomena. The
obtained results are in good agreement with experiments. An explicit proposal
is made to further check the theory.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
Fully Quantum Scalable Description of Driven-Dissipative Lattice Models
Methods for modeling large driven-dissipative quantum systems are becoming increasingly urgent due to recent experimental progress in a number of photonic platforms. We demonstrate the positive-P method to be ideal for this purpose across a wide range of parameters, focusing on the archetypal driven-dissipative Bose-Hubbard model. Notably, these parameters include intermediate regimes where interactions and dissipation are comparable, and especially cases with low occupations for which common semiclassical approximations can break down. The presence of dissipation can alleviate instabilities in the method that are known to occur for closed systems, allowing the simulation of dynamics up to and including the steady state. Throughout the parameter space of the model, we determine the magnitude of dissipation that is sufficient to make the method useful and stable, finding its region of applicability to be complementary to that of the truncated Wigner method. We then demonstrate its use in a number of examples with nontrivial quantum correlations, including a demonstration of solving the urgent open problem of large and highly nonuniform systems with tens of thousands of sites
Long-time behavior of the momentum distribution during the sudden expansion of a spin-imbalanced Fermi gas in one dimension
We study the sudden expansion of spin-imbalanced ultracold lattice fermions
with attractive interactions in one dimension after turning off the
longitudinal confining potential. We show that the momentum distribution
functions of majority and minority fermions approach stationary values quickly
due to a quantum distillation mechanism that results in a spatial separation of
pairs and majority fermions. As a consequence, Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) correlations are lost during the expansion. Furthermore, we argue that
the shape of the stationary momentum distribution functions can be understood
by relating them to the integrals of motion in this integrable quantum system.
We discuss our results in the context of proposals to observe FFLO
correlations, related to recent experiments by Liao et al., Nature 467, 567
(2010).Comment: 8 pages including supplementary material, 9 eps figures, revised
version as published, some text moved to the supplemental materia
Atividades de estágio em melhoramento genético de triticale e de centeio.
Orientador: Alfredo do Nascimento Junior
Indução e caracterização da fusariose em espigas de triticale e centeio.
Orientador: Alfredo do Nascimento Junior
- …