166 research outputs found
Expansion dynamics in the one-dimensional Fermi-Hubbard model
Expansion dynamics of interacting fermions in a lattice are simulated within
the one-dimensional (1D) Hubbard model, using the essentially exact
time-evolving block decimation (TEBD) method. In particular, the expansion of
an initial band-insulator state is considered. We analyze the simulation
results based on the dynamics of a two-site two-particle system, the so-called
Hubbard dimer. Our findings describe essential features of a recent experiment
on the expansion of a Fermi gas in a two-dimensional lattice. We show that the
Hubbard-dimer dynamics, combined with a two-fluid model for the paired and
non-paired components of the gas, gives an efficient description of the full
dynamics. This should be useful for describing dynamical phenomena of strongly
interacting Fermions in a lattice in general.Comment: Fig. 9 changed, text + supplementary material revise
Metsän arvoketjujen aluetaloudelliset vaikutukset Etelä- ja Keski-Pohjanmaalla - puurakentaminen ja yhdistetty lämmön ja sähkön tuotanto
Exotic superfluid states of lattice fermions in elongated traps
We present real-space dynamical mean-field theory calculations for
attractively interacting fermions in three-dimensional lattices with elongated
traps. The critical polarization is found to be 0.8, regardless of the trap
elongation. Below the critical polarization, we find unconventional superfluid
structures where the polarized superfluid and
Fulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core
region
Coexistence of pairing gaps in three-component Fermi gases
We study a three-component superfluid Fermi gas in a spherically symmetric
harmonic trap using the Bogoliubov-deGennes method. We predict a coexistence
phase in which two pairing field order parameters are simultaneously nonzero,
in stark contrast to studies performed for trapped gases using local density
approximation. We also discuss the role of atom number conservation in the
context of a homogeneous system.Comment: Text revised, added two figures and three reference
Experimentally realizable quantum comparison of coherent states and its applications
When comparing quantum states to each other, it is possible to obtain an
unambiguous answer, indicating that the states are definitely different,
already after a single measurement. In this paper we investigate comparison of
coherent states, which is the simplest example of quantum state comparison for
continuous variables. The method we present has a high success probability, and
is experimentally feasible to realize as the only required components are beam
splitters and photon detectors. An easily realizable method for quantum state
comparison could be important for real applications. As examples of such
applications we present a "lock and key" scheme and a simple scheme for quantum
public key distribution.Comment: 14 pages, 5 figures, version one submitted to PRA. Version two is the
final accepted versio
Vacuum Rabi splitting and strong coupling dynamics for surface plasmon polaritons and Rhodamine 6G molecules
We report on strong coupling between surface plasmon polaritons (SPP) and
Rhodamine 6G (R6G) molecules, with double vacuum Rabi splitting energies up to
230 and 110 meV. In addition, we demonstrate the emission of all three energy
branches of the strongly coupled SPP-exciton hybrid system, revealing features
of system dynamics that are not visible in conventional reflectometry. Finally,
in analogy to tunable-Q microcavities, we show that the Rabi splitting can be
controlled by adjusting the interaction time between waveguided SPPs and R6G
deposited on top of the waveguide. The interaction time can be controlled with
sub-fs precision by adjusting the length of the R6G area with standard
lithography methods.Comment: 4 pages, 4 figure
Hopping modulation in a one-dimensional Fermi-Hubbard Hamiltonian
We consider a strongly repulsive two-component Fermi gas in a one-dimensional
(1D) optical lattice described in terms of a Hubbard Hamiltonian. We analyze
the response of the system to a periodic modulation of the hopping amplitude in
presence of large two body interaction. By (essentially) exact simulations of
the time evolution, we find a non-trivial double occupancy frequency
dependence. We show how the dependence relates to the spectral features of the
system given by the Bethe ansatz. The discrete nature of the spectrum is
clearly reflected in the double occupancy after long enough modulation time. We
also discuss the implications of the 1D results to experiments in higher
dimensional systems.Comment: 4 pages, 5 figures; minor changes in the text, updated references
Simulation of quantum random walks using interference of classical field
We suggest a theoretical scheme for the simulation of quantum random walks on
a line using beam splitters, phase shifters and photodetectors. Our model
enables us to simulate a quantum random walk with use of the wave nature of
classical light fields. Furthermore, the proposed set-up allows the analysis of
the effects of decoherence. The transition from a pure mean photon-number
distribution to a classical one is studied varying the decoherence parameters.Comment: extensively revised version; title changed; to appear on Phys. Rev.
Laser-induced collective excitations in a two-component Fermi gas
We consider the linear density response of a two-component (superfluid) Fermi
gas of atoms when the perturbation is caused by laser light. We show that
various types of laser excitation schemes can be transformed into linear
density perturbations, however, a Bragg spectroscopy scheme is needed for
transferring energy and momentum into a collective mode. This makes other types
of laser probing schemes insensitive for collective excitations and therefore
well suited for the detection of the superfluid order parameter. We show that
for the special case when laser light is coupled between the two components of
the Fermi gas, density response is always absent in a homogeneous system.Comment: 6 pages, no figure
Induced interactions for ultracold Fermi gases in optical lattices
We investigate the effect of optical lattices on the BCS superfluidity by
using the Gorkov--Melik-Barkhudarov (GMB) correction for a two-component Fermi
gas. We find that the suppression of the order parameter is strongly enhanced
by the lattice effects. The predictions made by the GMB corrections are in
qualitative and, for the cases studied, quantitative agreement with previous
quantum Monte Carlo results. We discuss how the GMB correction extends the
validity of the mean-field theory to a wider range of tunable optical lattice
systems in different dimensions.Comment: 4 pages, 4 figure
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