21 research outputs found
Nonequilibrium thermal Casimir-Polder forces
We study the nonequilibrium Casimir-Polder force on an atom prepared in an
incoherent superposition of internal energy-eigenstates, which is placed in a
magnetoelectric environment of nonuniform temperature. After solving the
coupled atom--field dynamics within the framework of macroscopic quantum
electrodynamics, we derive a general expression for the thermal Casimir-Polder
force.Comment: 5 page
Casimir forces from a loop integral formulation
We reformulate the Casimir force in the presence of a non-trivial background.
The force may be written in terms of loop variables, the loop being a curve
around the scattering sites. A natural path ordering of exponentials take place
when a particular representation of the scattering centres is given. The basic
object to be evaluated is a reduced (or abbreviated) classical pseudo-action
that can be operator valued.Comment: references added, text clarified in place
Surface-induced heating of cold polar molecules
We study the rotational and vibrational heating of diatomic molecules placed
near a surface at finite temperature on the basis of macroscopic quantum
electrodynamics. The internal molecular evolution is governed by transition
rates that depend on both temperature and position. Analytical and numerical
methods are used to investigate the heating of several relevant molecules near
various surfaces. We determine the critical distances at which the surface
itself becomes the dominant source of heating and we investigate the transition
between the long-range and short-range behaviour of the heating rates. A simple
formula is presented that can be used to estimate the surface-induced heating
rates of other molecules of interest. We also consider how the heating depends
on the thickness and composition of the surface.Comment: 17 pages, 7 figure
Casimir force on amplifying bodies
Based on a unified approach to macroscopic QED that allows for the inclusion
of amplification in a limited space and frequency range, we study the Casimir
force as a Lorentz force on an arbitrary partially amplifying system of
linearly locally responding (isotropic) magnetoelectric bodies. We demonstrate
that the force on a weakly polarisable/magnetisable amplifying object in the
presence of a purely absorbing environment can be expressed as a sum over the
Casimir--Polder forces on the excited atoms inside the body. As an example, the
resonant force between a plate consisting of a dilute gas of excited atoms and
a perfect mirror is calculated
Non-equilibrium Casimir forces: Spheres and sphere-plate
We discuss non-equilibrium extensions of the Casimir force (due to
electromagnetic fluctuations), where the objects as well as the environment are
held at different temperatures. While the formalism we develop is quite
general, we focus on a sphere in front of a plate, as well as two spheres, when
the radius is small compared to separation and thermal wavelengths. In this
limit the forces can be expressed analytically in terms of the lowest order
multipoles, and corroborated with results obtained by diluting parallel plates
of vanishing thickness. Non-equilibrium forces are generally stronger than
their equilibrium counterpart, and may oscillate with separation (at a scale
set by material resonances). For both geometries we obtain stable points of
zero net force, while two spheres may have equal forces in magnitude and
direction resulting in a self-propelling state.Comment: 6 pages, 6 figure
Fluctuations, dissipation and the dynamical Casimir effect
Vacuum fluctuations provide a fundamental source of dissipation for systems
coupled to quantum fields by radiation pressure. In the dynamical Casimir
effect, accelerating neutral bodies in free space give rise to the emission of
real photons while experiencing a damping force which plays the role of a
radiation reaction force. Analog models where non-stationary conditions for the
electromagnetic field simulate the presence of moving plates are currently
under experimental investigation. A dissipative force might also appear in the
case of uniform relative motion between two bodies, thus leading to a new kind
of friction mechanism without mechanical contact. In this paper, we review
recent advances on the dynamical Casimir and non-contact friction effects,
highlighting their common physical origin.Comment: 39 pages, 4 figures. Review paper to appear in Lecture Notes in
Physics, Volume on Casimir Physics, edited by Diego Dalvit, Peter Milonni,
David Roberts, and Felipe da Rosa. Minor changes, a reference adde