406 research outputs found
The virtual photon approximation for three-body interatomic Coulombic decay
Interatomic Coulombic decay (ICD) is a mechanism which allows microscopic
objects to rapidly exchange energy. When the two objects are distant, the
energy transfer between the donor and acceptor species takes place via the
exchange of a virtual photon. On the contrary, recent ab initio calculations
have revealed that the presence of a third passive species can significantly
enhance the ICD rate at short distances due to the effects of electronic wave
function overlap and charge transfer states [Phys. Rev. Lett. 119, 083403
(2017)]. Here, we develop a virtual photon description of three-body ICD,
showing that a mediator atom can have a significant influence at much larger
distances. In this regime, this impact is due to the scattering of virtual
photons off the mediator, allowing for simple analytical results and being
manifest in a distinct geometry-dependence which includes interference effects.
As a striking example, we show that in the retarded regime ICD can be
substantially enhanced or suppressed depending on the position of the
ICD-inactive object, even if the latter is far from both donor and acceptor
species
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
Tuning the collective decay of two entangled emitters by means of a nearby surface
We consider the radiative properties of a system of two identical correlated
atoms interacting with the electromagnetic field in its vacuum state in the
presence of a generic dielectric environment. We suppose that the two emitters
are prepared in a symmetric or antisymmetric superposition of one ground state
and one excited state and we evaluate the transition rate to the collective
ground state, showing distinctive cooperative radiative features. Using a
macroscopic quantum electrodynamics approach to describe the electromagnetic
field, we first obtain an analytical expression for the decay rate of the two
entangled two-level atoms in terms of the Green's tensor of the generic
external environment. We then investigate the emission process when both atoms
are in free space and subsequently when a perfectly reflecting mirror is
present, showing how the boundary affects the physical features of the
superradiant and subradiant emission by the two coupled emitters. The
possibility to control and tailor radiative processes is also discussed.Comment: 11 pages, 8 figure
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
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
Matter-screened Casimir force and Casimir-Polder force in planar structures
Using a recently developed theory of the Casimir force (Raabe C and Welsch
D-G 2005 Phys. Rev. A 71 013814), we calculate the force that acts on a plate
in front of a planar wall and the force that acts on the plate in the case
where the plate is part of matter that fills the space in front of the wall. We
show that in the limit of a dielectric plate whose permittivity is close to
unity, the force obtained in the former case reduces to the ordinary, i.e.,
unscreened Casimir-Polder force acting on isolated atoms. In the latter case,
the theory yields the Casimir-Polder force that is screened by the surrounding
matter.Comment: 11 pages, 1 figure -- published online at J. Opt. B on Nov 16 200
Ground-state van der Waals forces in planar multilayer magnetodielectrics
Within the frame of lowest-order perturbation theory, the van der Waals
potential of a ground-state atom placed within an arbitrary dispersing and
absorbing magnetodielectric multilayer system is given. Examples of an atom
situated in front of a magnetodielectric plate or between two such plates are
studied in detail. Special emphasis is placed on the competing attractive and
repulsive force components associated with the electric and magnetic matter
properties, respectively, and conditions for the formation of repulsive
potential walls are given. Both numerical and analytical results are presented.Comment: 16 pages, 8 figures, minor correction
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