1,866 research outputs found
Attractive Optical Forces from Blackbody Radiation
Blackbody radiation around hot objects induces ac Stark shifts of the energy
levels of nearby atoms and molecules. These shifts are roughly proportional to
the fourth power of the temperature and induce a force decaying with the third
power of the distance from the object. We explicitly calculate the resulting
attractive blackbody optical dipole force for ground state hydrogen atoms.
Surprisingly, this force can surpass the repulsive radiation pressure and
actually pull the atoms against the radiation energy flow towards the surface
with a force stronger than gravity. We exemplify the dominance of the
"blackbody force" over gravity for hydrogen in a cloud of hot dust particles.
This overlooked force appears relevant in various astrophysical scenarios, in
particular, since analogous results hold for a wide class of other broadband
radiation sources
Self-organised Limit-Cycles, Chaos and Phase-Slippage with a Superfluid inside an Optical Resonator
We study dynamical phases of a driven Bose-Einstein condensate coupled to the
light field of a high-Q optical cavity. For high field seeking atoms at red
detuning the system is known to show a transition from a spatially homogeneous
steady-state to a self-organized regular lattice exhibiting super-radiant
scattering into the cavity. For blue atom pump detuning the particles are
repelled from the maxima of the light-induced optical potential suppressing
scattering. We show that this generates a new dynamical instability of the
self-ordered phase, leading to the appearance of self-ordered stable
limit-cycles characterized by large amplitude self-sustained oscillations of
both the condensate density and cavity field. The limit-cycles evolve into
chaotic behavior by period doubling. Large amplitude oscillations of the
condensate are accompanied by phase-slippage through soliton nucleation at a
rate which increases by orders of magnitude in the chaotic regime. Different
from a superfluid in a closed setup, this driven dissipative superfluid is not
destroyed by the proliferation of solitons since kinetic energy is removed
through cavity losses.Comment: 4 figure
Generalized mean-field approach to simulate large dissipative spin ensembles with long range interactions
We simulate the collective dynamics in spin lattices with long range
interactions and collective decay in one, two and three dimensions. Starting
from a dynamical mean-field approach derived by local factorization of the
density operator we improve the numerical approximation of the full master
equation by including pair correlations at any distance. This truncations
enable us to drastically increase the number of spins in our numerical
simulations from about ten spins in case of the full quantum model to several
ten-thousands in the mean-field approximation and a few hundreds if pair
correlations are included. Extensive numerical tests help us identify
interaction strengths and geometric configurations where these approximations
perform well and allow us to state fairly simple error estimates. By simulating
systems of increasing size we show that in one and two dimensions we can
include as many spins as needed to capture the properties of infinite size
systems with high accuracy, while in 3D the method does not converge to desired
accuracy within the system sizes we can currently implement. Our approach is
well suited to give error estimates of magic wavelength optical lattices for
atomic clock applications and corresponding super radiant lasers
Collective Enhancement and Suppression of Excitation Decay in Optical Lattices
We calculate radiative lifetimes of collective electronic excitations of
atoms in an infinite one dimensional lattice. The translational symmetry along
the lattice restricts the photon wave vector component parallel to the lattice
to the exciton wave number and thus the possible emission directions. The
resulting radiation damping rate and emission pattern of the exciton strongly
deviates from independent atom. For some wave numbers and polarizations the
excitons superradiantly decay very fast, while other excitons show zero
radiation damping rate and form propagating meta-stable excitations. Such
states could be directly coupled via tailored evanescent fields from a nearby
fiber.Comment: 4 pages, 7 figure
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