310 research outputs found
Quasiparticle Berry curvature and Chern numbers in spin-orbit coupled bosonic Mott insulators
We study the ground-state topology and quasiparticle properties in bosonic
Mott insulators with two- dimensional spin-orbit couplings in cold atomic
optical lattices. We show that the many-body Chern and spin-Chern number can be
expressed as an integral of the quasihole Berry curvatures over the Brillouin
zone. Using a strong-coupling perturbation theory, for an experimentally
feasible spin-orbit coupling, we compute the Berry curvature and the spin Chern
number and find that these quantities can be generated purely by interactions.
We also compute the quasiparticle dispersions, spectral weights, and the
quasimomentum space distribution of particle and spin density, which can be
accessed in cold-atom experiments and used to deduce the Berry curvature and
Chern numbers
Many-body aspects of coherent atom-molecule oscillations
We study the many-body effects on coherent atom-molecule oscillations by
means of an effective quantum field theory that describes Feshbach-resonant
interactions in Bose gases in terms of an atom-molecule hamiltonian. We
determine numerically the many-body corrections to the oscillation frequency
for various densities of the atomic condensate. We also derive an analytic
expression that approximately describes both the density and magnetic-field
dependence of this frequency near the resonance. We find excellent agreement
with experiment.Comment: 4 pages, revtex 4, v2: minor changes: corrected some typos/omissions,
Discarded use of the term 'Rabi frequency' to avoid confusio
Microscopic many-body theory of atomic Bose gases near a Feshbach resonance
A Feshbach resonance in the s-wave scattering length occurs if the energy of
the two atoms in the incoming open channel is close to the energy of a bound
state in a coupled closed channel. Starting from the microscopic hamiltonian
that describes this situation, we derive the effective atom-molecule theory for
a Bose gas near a Feshbach resonance. In order to take into account all
two-body processes, we have to dress the bare couplings of the atom-molecule
model with ladder diagrams. This results in a quantum field theory that exactly
reproduces the scattering amplitude of the atoms and the bound-state energy of
the molecules. Since these properties are incorporated at the quantum level,
the theory can be applied both above and below the critical temperature of the
gas. Moreover, making use of the true interatomic potentials ensures that no
divergences are encountered at any stage of the calculation. We also present
the mean-field theory for the Bose-Einstein condensed phase of the gas.Comment: Submitted to the Journal of Optics B special issue on the 7th
International Workshop on Atom Optics and Interferometr
Quantum vortex dynamics in two-dimensional neutral superfluids
We derive an effective action for the vortex position degree-of-freedom in a
superfluid by integrating out condensate phase and density fluctuation
environmental modes. When the quantum dynamics of environmental fluctuations is
neglected, we confirm the occurrence of the vortex Magnus force and obtain an
expression for the vortex mass. We find that this adiabatic approximation is
valid only when the superfluid droplet radius , or the typical distance
between vortices, is very much larger than the coherence length . We go
beyond the adiabatic approximation numerically, accounting for the quantum
dynamics of environmental modes and capturing their dissipative coupling to
condensate dynamics. For the case of an optical-lattice superfluid we
demonstrate that vortex motion damping can be adjusted by tuning the ratio
between the tunneling energy and the on-site interaction energy . We
comment on the possibility of realizing vortex Landau level physics.Comment: 14 pages, 10 figures, accepted by PRA with corrected references and
typo
Hydrodynamic modes of partially condensed Bose mixtures
We generalize the Landau-Khalatnikov hydrodynamic theory for superfluid
helium to two-component (binary) Bose mixtures at arbitrary temperatures. In
particular, we include the spin-drag terms that correspond to viscous coupling
between the clouds. Therefore, our theory not only describes the usual
collective modes of the individual components, e.g., first and second sound,
but also results in new collective modes, where both constituents participate.
We study these modes in detail and present their dispersions using
thermodynamic quantities obtained within the Popov approximation
Quantitative Probe of Pairing Correlations in a Cold Fermionic Atom Gas
A quantitative measure of the pairing correlations present in a cold gas of
fermionic atoms can be obtained by studying the dependence of RF spectra on
hyperfine state populations. This proposal follows from a sum rule that relates
the total interaction energy of the gas to RF spectrum line positions. We argue
that this indicator of pairing correlations provides information comparable to
that available from the spin-susceptibility and NMR measurements common in
condensed-matter systems.Comment: 5 pages, 1 figur
Schwinger-Keldysh theory for Bose-Einstein condensation of photons in a dye-filled optical microcavity
We consider Bose-Einstein condensation of photons in an optical cavity filled
with dye molecules that are excited by laser light. By using the
Schwinger-Keldysh formalism we derive a Langevin field equation that describes
the dynamics of the photon gas, and in particular its equilibrium properties
and relaxation towards equilibrium. Furthermore we show that the finite
lifetime effects of the photons are captured in a single dimensionless damping
parameter, that depends on the power of the external laser pumping the dye.
Finally, as applications of our theory we determine spectral functions and
collective modes of the photon gas in both the normal and the Bose-Einstein
condensed phase
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