1,392 research outputs found
Optomechanics with molecules in a strongly pumped ring cavity
Cavity cooling of an atom works best on a cyclic optical transition in the
strong coupling regime near resonance, where small cavity photon numbers
suffice for trapping and cooling. Due to the absence of closed transitions a
straightforward application to molecules fails: optical pumping can lead the
particle into uncoupled states. An alternative operation in the far
off-resonant regime generates only very slow cooling due to the reduced
field-molecule coupling. We predict to overcome this by using a strongly driven
ring-cavity operated in the sideband cooling regime. As in the optomechanical
setups one takes advantage of a collectively enhanced field-molecule coupling
strength using a large photon number. A linearized analytical treatment
confirmed by full numerical quantum simulations predicts fast cooling despite
the off-resonant small single molecule - single photon coupling. Even ground
state cooling can be obtained by tuning the cavity field close to the
Anti-stokes sideband for sufficiently high trapping frequency. Numerical
simulations show quantum jumps of the molecules between the lowest two trapping
levels, which can be be directly and continuously monitored via scattered light
intensity detection
Observation of decoherence with a movable mirror
Recently it has been proposed to use parity as a measure of the mechanism
behind decoherence or the transformation from quantum to classical. Here, we
show that the proposed experiment is more feasible than previously thought, as
even an initial thermal state would exhibit the hypothesized symmetry breaking.Comment: Proceedings of the Lake Garda "quantum puzzles" conferenc
Exciton-Polariton scattering for defect detection in cold atom Optical Lattices
We study the effect of defects in the Mott insulator phase of ultracold atoms
in an optical lattice on the dynamics of resonant excitations. Defects, which
can either be empty sites in a Mott insulator state with one atom per site or a
singly occupied site for a filling factor two, change the dynamics of Frenkel
excitons and cavity polaritons. While the vacancies in first case behave like
hard sphere scatters for excitons, singly occupied sites in the latter case can
lead to attractive or repulsive scattering potentials. We suggest cavity
polaritons as observation tool of such defects, and show how the scattering can
be controlled in changing the exciton-photon detuning. In the case of
asymmetric optical lattice sites we present how the scattering effective
potential can be detuned by the cavity photon polarization direction, with the
possibility of a crossover from a repulsive into an attractive potential.Comment: 9 pages, 10 figure
Self-organization of atoms in a cavity field: threshold, bistability and scaling laws
We present a detailed study of the spatial self-organization of laser-driven
atoms in an optical cavity, an effect predicted on the basis of numerical
simulations [P. Domokos and H. Ritsch, Phys. Rev. Lett. 89, 253003 (2002)] and
observed experimentally [A. T. Black et al., Phys. Rev. Lett. 91, 203001
(2003)]. Above a threshold in the driving laser intensity, from a uniform
distribution the atoms evolve into one of two stable patterns that produce
superradiant scattering into the cavity. We derive analytic formulas for the
threshold and critical exponent of this phase transition from a mean-field
approach. Numerical simulations of the microscopic dynamics reveal that, on
laboratory timescale, a hysteresis masks the mean-field behaviour. Simple
physical arguments explain this phenomenon and provide analytical expressions
for the observable threshold. Above a certain density of the atoms a limited
number of ``defects'' appear in the organized phase, and influence the
statistical properties of the system. The scaling of the cavity cooling
mechanism and the phase space density with the atom number is also studied.Comment: submitted to PR
Enhancing interferometric sensitivity by non-classical light from quantum non-demolition measurements in cavity QED
We propose an enhanced optical interferometer based on tailored non-classical
light generated by nonlinear dynamics and projective measurements in a
three-level atom cavity QED system. A coherent state in the cavity becomes
dynamically entangled with two ground states of the atom and is transformed to
a macroscopic superposition state via a projective measurement on the atom. We
show that the resulting highly non-classical state can improve interferometric
precision measurements well beyond the shot-noise limit once combined with a
classical laser pulse at the input of a Mach-Zehnder interferometer. For a
practical implementation, we identify an efficient phase shift estimation
scheme based on the counting of photons at the interferometer output. Photon
losses and photon-counting errors deteriorate the interferometer sensitivity,
but we demonstrate that it still can be significantly better than the
shot-noise limit under realistic conditions.Comment: 9 pages, 10 figure
Collective excitations and instability of an optical lattice due to unbalanced pumping
We solve self-consistently the coupled equations of motion for trapped
particles and the field of a one-dimensional optical lattice. Optomechanical
coupling creates long-range interaction between the particles, whose nature
depends crucially on the relative power of the pump beams. For asymmetric
pumping, traveling density wave-like collective oscillations arise in the
lattice, even in the overdamped limit. Increasing the lattice size or pump
asymmetry these waves can destabilize the lattice.Comment: 5 pages, minor changes (SI units, new references
Optomechanical deformation and strain in elastic dielectrics
Light forces induced by scattering and absorption in elastic dielectrics lead
to local density modulations and deformations. These perturbations in turn
modify light propagation in the medium and generate an intricate nonlinear
response. We generalise an analytic approach where light propagation in
one-dimensional media of inhomogeneous density is modelled as a result of
multiple scattering between polarizable slices. Using the Maxwell stress tensor
formalism we compute the local optical forces and iteratively approach
self-consistent density distributions where the elastic back-action balances
gradient- and scattering forces. For an optically trapped dielectric we derive
the nonlinear dependence of trap position, stiffness and total deformation on
the object's size and field configuration. Generally trapping is enhanced by
deformation, which exhibits a periodic change between stretching and
compression. This strongly deviates from qualitative expectations based on the
change of photon momentum of light crossing the surface of a dielectric. We
conclude that optical forces have to be treated as volumetric forces and that a
description using the change of photon momentum at the surface of a medium is
inappropriate
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