1,328 research outputs found
Atom-molecule dark states in a Bose-Einstein condensate
We have created a dark quantum superposition state of a Rb Bose-Einstein
condensate (BEC) and a degenerate gas of Rb ground state molecules in a
specific ro-vibrational state using two-color photoassociation. As a signature
for the decoupling of this coherent atom-molecule gas from the light field we
observe a striking suppression of photoassociation loss. In our experiment the
maximal molecule population in the dark state is limited to about 100 Rb
molecules due to laser induced decay. The experimental findings can be well
described by a simple three mode model.Comment: 4 pages, 6 figure
Light scattering from ultracold atoms in optical lattices as an optical probe of quantum statistics
We study off-resonant collective light scattering from ultracold atoms
trapped in an optical lattice. Scattering from different atomic quantum states
creates different quantum states of the scattered light, which can be
distinguished by measurements of the spatial intensity distribution, quadrature
variances, photon statistics, or spectral measurements. In particular,
angle-resolved intensity measurements reflect global statistics of atoms (total
number of radiating atoms) as well as local statistical quantities (single-site
statistics even without an optical access to a single site) and pair
correlations between different sites. As a striking example we consider
scattering from transversally illuminated atoms into an optical cavity mode.
For the Mott insulator state, similar to classical diffraction, the number of
photons scattered into a cavity is zero due to destructive interference, while
for the superfluid state it is nonzero and proportional to the number of atoms.
Moreover, we demonstrate that light scattering into a standing-wave cavity has
a nontrivial angle dependence, including the appearance of narrow features at
angles, where classical diffraction predicts zero. The measurement procedure
corresponds to the quantum non-demolition (QND) measurement of various atomic
variables by observing light.Comment: 15 pages, 5 figure
Hofstadter butterfly in a cavity-induced dynamic synthetic magnetic field
Energy bands of electrons in a square lattice potential threaded by a uniform magnetic field exhibit a fractal structure known as the Hofstadter butterfly. Here we study a Fermi gas in a 2D optical lattice within a linear cavity with a tilt along the cavity axis. The hopping along the cavity axis is only induced by resonant Raman scattering of transverse pump light into a standing-wave-cavity mode. Choosing a suitable pump geometry allows us to realize the Hofstadter-Harper model with a cavity-induced dynamical synthetic magnetic field, which appears at the onset of the superradiant phase transition. The dynamical nature of this cavity-induced synthetic magnetic field arises from the delicate interplay between collective superradiant scattering and the underlying fractal band structure. Using a sixth-order expansion of the free energy as a function of the order parameter and by numerical simulations, we show that at low magnetic fluxes the superradiant ordering phase transition is first order, while it becomes second order for higher flux. The dynamic nature of the magnetic field induces a nontrivial deformation of the Hofstadter butterfly in the superradiant phase. At strong pump far above the self-ordering threshold, we recover the Hofstadter butterfly one would obtain in a static magnetic field
Strong magnetic coupling of an ultracold gas to a superconducting waveguide cavity
Placing an ensemble of ultracold atoms in the near field of a
superconducting coplanar waveguide resonator (CPWR) with one can
achieve strong coupling between a single microwave photon in the CPWR and a
collective hyperfine qubit state in the ensemble with kHz larger than the cavity line width of
kHz. Integrated on an atomchip such a system constitutes a hybrid quantum
device, which also can be used to interconnect solid-state and atomic qubits,
to study and control atomic motion via the microwave field, observe microwave
super-radiance, build an integrated micro maser or even cool the resonator
field via the atoms
Prospects for the cavity-assisted laser cooling of molecules
Cooling of molecules via free-space dissipative scattering of photons is
thought not to be practicable due to the inherently large number of Raman loss
channels available to molecules and the prohibitive expense of building
multiple repumping laser systems. The use of an optical cavity to enhance
coherent Rayleigh scattering into a decaying cavity mode has been suggested as
a potential method to mitigate Raman loss, thereby enabling the laser cooling
of molecules to ultracold temperatures. We discuss the possibility of
cavity-assisted laser cooling particles without closed transitions, identify
conditions necessary to achieve efficient cooling, and suggest solutions given
experimental constraints. Specifically, it is shown that cooperativities much
greater than unity are required for cooling without loss, and that this could
be achieved via the superradiant scattering associated with intracavity
self-localization of the molecules. Particular emphasis is given to the polar
hydroxyl radical (OH), cold samples of which are readily obtained from Stark
deceleration.Comment: 18 pages, 10 figure
Master Equation for the Motion of a Polarizable Particle in a Multimode Cavity
We derive a master equation for the motion of a polarizable particle weakly
interacting with one or several strongly pumped cavity modes. We focus here on
massive particles with complex internal structure such as large molecules and
clusters, for which we assume a linear scalar polarizability mediating the
particle-light interaction. The predicted friction and diffusion coefficients
are in good agreement with former semiclassical calculations for atoms and
small molecules in weakly pumped cavities, while the current rigorous quantum
treatment and numerical assessment sheds a light on the feasibility of
experiments that aim at optically manipulating beams of massive molecules with
multimode cavities.Comment: 30 pages, 5 figure
Collective Electronic Excitation Coupling between Planar Optical Lattices using Ewald's Method
Using Ewald's summation method we investigate collective electronic
excitations (excitons) of ultracold atoms in parallel planar optical lattices
including long range interactions. The exciton dispersion relation can then be
suitably rewritten and efficiently calculated for long range resonance
dipole-dipole interactions. Such in-plane excitons resonantly couple for two
identical optical lattices, with an energy transfer strength decreasing
exponentially with the distance between the lattices. This allows a restriction
of the transfer to neighboring planes and gives rise to excitons delocalized
between the lattices. In general equivalent results will hold for any planar
system containing lattice layers of optically active and dipolar materials.Comment: 6 pages, and 7 figure
Optical Properties of Collective Excitations for Finite Chains of Trapped Atoms
Resonant dipole-dipole interaction modifies the energy and decay rate of
electronic excitations for finite one dimensional chains of ultracold atoms in
an optical lattice. We show that collective excited states of the atomic chain
can be divided into dark and bright modes, where a superradiant mode with an
enhanced collective effective dipole dominates the optical scattering. Studying
the generic case of two chain segments of different length and position
exhibits an interaction blockade and spatially structured light emission.
Ultimately, an extended system of several interfering segments models a long
chain with randomly distributed defects of vacant sites. The corresponding
emission pattern provides a sensitive tool to study structural and dynamical
properties of the system.Comment: 8 pages, 12 figure
Influence of a Feshbach resonance on the photoassociation of LiCs
We analyse the formation of ultracold 7Li133Cs molecules in the rovibrational
ground state through photoassociation into the B1Pi state, which has recently
been reported [J. Deiglmayr et al., Phys. Rev. Lett. 101, 133004 (2008)].
Absolute rate constants for photoassociation at large detunings from the atomic
asymptote are determined and are found to be surprisingly large. The
photoassociation process is modeled using a full coupled-channel calculation
for the continuum state, taking all relevant hyperfine states into account. The
enhancement of the photoassociation rate is found to be caused by an `echo' of
the triplet component in the singlet component of the scattering wave function
at the inner turning point of the lowest triplet a3Sigma+ potential. This
perturbation can be ascribed to the existence of a broad Feshbach resonance at
low scattering energies. Our results elucidate the important role of couplings
in the scattering wave function for the formation of deeply bound ground state
molecules via photoassociation.Comment: Added Erratum, 20 pages, 9 figure
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