8 research outputs found
Optical properties of atomic Mott insulators: from slow light to dynamical Casimir effects
We theoretically study the optical properties of a gas of ultracold,
coherently dressed three-level atoms in a Mott insulator phase of an optical
lattice. The vacuum state, the band dispersion and the absorption spectrum of
the polariton field can be controlled in real time by varying the amplitude and
the frequency of the dressing beam. In the weak dressing regime, the system
shows unique ultra-slow light propagation properties without absorption. In the
presence of a fast time modulation of the dressing amplitude, we predict a
significant emission of photon pairs by parametric amplification of the
polaritonic zero-point fluctuations. Quantitative considerations on the
experimental observability of such a dynamical Casimir effect are presented for
the most promising atomic species and level schemes
Thermal corrections to the Casimir effect
The Casimir effect, reflecting quantum vacuum fluctuations in the
electromagnetic field in a region with material boundaries, has been studied
both theoretically and experimentally since 1948. The forces between dielectric
and metallic surfaces both plane and curved have been measured at the 10 to 1
percent level in a variety of room-temperature experiments, and remarkable
agreement with the zero-temperature theory has been achieved. In fitting the
data various corrections due to surface roughness, patch potentials, curvature,
and temperature have been incorporated. It is the latter that is the subject of
the present article. We point out that, in fact, no temperature dependence has
yet been detected, and that the experimental situation is still too fluid to
permit conclusions about thermal corrections to the Casimir effect.
Theoretically, there are subtle issues concerning thermodynamics and
electrodynamics which have resulted in disparate predictions concerning the
nature of these corrections. However, a general consensus has seemed to emerge
that suggests that the temperature correction to the Casimir effect is
relatively large, and should be observable in future experiments involving
surfaces separated at the few micrometer scale.Comment: 21 pages, 9 eps figures, uses iopart.cls. Final version to be
published in New Journal of Physics, contains Conclusion and clarified
remark
Casimir forces and non-Newtonian gravitation
The search for non-relativistic deviations from Newtonian gravitation can
lead to new phenomena signalling the unification of gravity with the other
fundamental interactions. Various recent theoretical frameworks indicate a
possible window for non-Newtonian forces with gravitational coupling strength
in the micrometre range. The major expected background in the same range is
attributable to the Casimir force or variants of it if dielectric materials,
rather than conducting ones, are considered. Here we review the measurements of
the Casimir force performed so far in the micrometre range and how they
determine constraints on non-Newtonian gravitation, also discussing the
dominant sources of false signals. We also propose a geometry-independent
parameterization of all data in terms of the measurement of the constant c. Any
Casimir force measurement should lead, once all corrections are taken into
account, to a determination of the constant c which, in order to assess the
accuracy of the measurement, can be compared with its more precise value known
through microscopic measurements. Although the last decade of experiments has
resulted in solid demonstrations of the Casimir force, the situation is not
conclusive with respect to being able to discover new physics. Future
experiments and novel phenomenological analysis will be necessary to discover
non-Newtonian forces or to push the window for their possible existence into
regions of the parameter space which theoretically appear unnatural.Comment: Also available at http://www.iop.org/EJ/abstract/1367-2630/8/10/23