599 research outputs found
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
Selecting molecules in the vibrational and rotational ground state by deflection
A beam of diatomic molecules scattered off a standing wave laser mode splits
according to the rovibrational quantum state of the molecules. Our numerical
calculation shows that single state resolution can be achieved by properly
tuned, monochromatic light. The proposed scheme allows for selecting
non-vibrating and non-rotating molecules from a thermal beam, implementing a
laser Maxwell's demon to prepare a rovibrationally cold molecular ensemble.Comment: 11 pages, LaTeX. To appear in the European Physical Journal
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
Cooling trapped atoms in optical resonators
We derive an equation for the cooling dynamics of the quantum motion of an
atom trapped by an external potential inside an optical resonator. This
equation has broad validity and allows us to identify novel regimes where the
motion can be efficiently cooled to the potential ground state. Our result
shows that the motion is critically affected by quantum correlations induced by
the mechanical coupling with the resonator, which may lead to selective
suppression of certain transitions for the appropriate parameters regimes,
thereby increasing the cooling efficiency.Comment: 4 pages, 3 figures; version published in PR
How river rocks round: resolving the shape-size paradox
River-bed sediments display two universal downstream trends: fining, in which
particle size decreases; and rounding, where pebble shapes evolve toward
ellipsoids. Rounding is known to result from transport-induced abrasion;
however many researchers argue that the contribution of abrasion to downstream
fining is negligible. This presents a paradox: downstream shape change
indicates substantial abrasion, while size change apparently rules it out. Here
we use laboratory experiments and numerical modeling to show quantitatively
that pebble abrasion is a curvature-driven flow problem. As a consequence,
abrasion occurs in two well-separated phases: first, pebble edges rapidly round
without any change in axis dimensions until the shape becomes entirely convex;
and second, axis dimensions are then slowly reduced while the particle remains
convex. Explicit study of pebble shape evolution helps resolve the shape-size
paradox by reconciling discrepancies between laboratory and field studies, and
enhances our ability to decipher the transport history of a river rock.Comment: 11 pages, 5 figure
Parametric amplification of the mechanical vibrations of a suspended nanowire by magnetic coupling to a Bose-Einstein condensate
We consider the possibility of parametric amplification of a mechanical
vibration mode of a nanowire due to its interaction with a Bose-Einstein
condensate (BEC) of ultracold atoms. The magneto-mechanical coupling is
mediated by the vibrationally modulated magnetic field around the
current-carrying nanowire, which can induce atomic transitions between
different hyperfine sublevels. We theoretically analyze the limitations arising
from the fact that the spin inverted atomic medium which feeds the mechanical
oscillation has a finite bandwidth in the range of the chemical potential of
the condensate
A quantum homogeneous space of nilpotent matrices
A quantum deformation of the adjoint action of the special linear group on
the variety of nilpotent matrices is introduced. New non-embedded quantum
homogeneous spaces are obtained related to certain maximal coadjoint orbits,
and known quantum homogeneous spaces are revisited.Comment: 12 page
- âŚ