1,547 research outputs found
Dynamical polarizability of atoms in arbitrary light fields: general theory and application to cesium
We present a systematic derivation of the dynamical polarizability and the ac
Stark shift of the ground and excited states of atoms interacting with a
far-off-resonance light field of arbitrary polarization. We calculate the
scalar, vector, and tensor polarizabilities of atomic cesium using resonance
wavelengths and reduced matrix elements for a large number of transitions. We
analyze the properties of the fictitious magnetic field produced by the vector
polarizability in conjunction with the ellipticity of the polarization of the
light field.Comment: see also Supplemental Materia
Superconductivity and Pairing Fluctuations in the Half-Filled Two-Dimensional Hubbard Model
The two-dimensional Hubbard model exhibits superconductivity with d-wave
symmetry even at half-filling in the presence of next-nearest neighbor hopping.
Using plaquette cluster dynamical mean-field theory with a continuous-time
quantum Monte Carlo impurity solver, we reveal the non-Fermi liquid character
of the metallic phase in proximity to the superconducting state. Specifically,
the low-frequency scattering rate for momenta near (\pi, 0) varies
non-monotonously at low temperatures, and the dc conductivity is T-linear at
elevated temperatures with an upturn upon cooling. Evidence is provided that
pairing fluctuations dominate the normal-conducting state even considerably
above the superconducting transition temperature.Comment: 4.3 pages, 4 figure
Heating in Nanophotonic Traps for Cold Atoms
Laser-cooled atoms that are trapped and optically interfaced with light in
nanophotonic waveguides are a powerful platform for fundamental research in
quantum optics as well as for applications in quantum communication and quantum
information processing. Ever since the first realization of such a hybrid
quantum nanophotonic, heating rates of the atomic motion observed in various
experimental settings have typically been exceeding those in comparable
free-space optical microtraps by about three orders of magnitude. This
excessive heating is a roadblock for the implementation of certain protocols
and devices. Its origin has so far remained elusive and, at the typical
atom-surface separations of less than an optical wavelength encountered in
nanophotonic traps, numerous effects may potentially contribute to atom
heating. Here, we theoretically describe the effect of mechanical vibrations of
waveguides on guided light fields and provide a general theory of
particle-phonon interaction in nanophotonic traps. We test our theory by
applying it to the case of laser-cooled cesium atoms in nanofiber-based
two-color optical traps. We find excellent quantitative agreement between the
predicted heating rates and experimentally measured values. Our theory predicts
that, in this setting, the dominant heating process stems from the
optomechanical coupling of the optically trapped atoms to the continuum of
thermally occupied flexural mechanical modes of the waveguide structure. Beyond
unraveling the long-standing riddle of excessive heating in nanofiber-based
atom traps, we also study the dependence of the heating rates on the relevant
system parameters. Our findings allow us to propose several strategies for
minimizing the heating. Finally, our findings are also highly relevant for
optomechanics experiments with dielectric nanoparticles that are optically
trapped close to nanophotonic waveguides.Comment: Published version. 35 pages (including appendices), 7 figures, 18
tables, and 3 pages of supplemental materia
Correlations in a band insulator
We study a model of a covalent band insulator with on-site Coulomb repulsion
at half-filling using dynamical mean-field theory. Upon increasing the
interaction strength the system undergoes a discontinuous transition from a
correlated band insulator to a Mott insulator with hysteretic behavior at low
temperatures. Increasing the temperature in the band insulator close to the
insulator-insulator transition we find a crossover to a Mott insulator at
elevated temperatures. Remarkably, correlations decrease the energy gap in the
correlated band insulator. The gap renormalization can be traced to the
low-frequency behavior of the self-energy, analogously to the quasiparticle
renormalization in a Fermi liquid. While the uncorrelated band insulator is
characterized by a single gap for both charge and spin excitations, the spin
gap is smaller than the charge gap in the correlated system.Comment: 7 pages, 7 figure
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