1,916 research outputs found
Nonlocal properties of dynamical three-body Casimir-Polder forces
We consider the three-body Casimir-Polder interaction between three atoms
during their dynamical self-dressing. We show that the time-dependent
three-body Casimir-Polder interaction energy displays nonlocal features related
to quantum properties of the electromagnetic field and to the nonlocality of
spatial field correlations. We discuss the measurability of this intriguing
phenomenon and its relation with the usual concept of stationary three-body
forces.Comment: 4 page
Spontaneous emission of an atom near an oscillating mirror
We investigate the spontaneous emission of one atom placed near an oscillating reflecting plate. We consider the atom modeled as a two-level system, interacting with the quantum electromagnetic field in the vacuum state, in the presence of the oscillating mirror. We suppose that the plate oscillates adiabatically, so that the time-dependence of the interaction Hamiltonian is entirely enclosed in the time-dependent mode functions, satisfying the boundary conditions at the plate surface, at any given time. Using time-dependent perturbation theory, we evaluate the transition rate to the ground-state of the atom, and show that it depends on the time-dependent atom-plate distance. We also show that the presence of the oscillating mirror significantly affects the physical features of the spontaneous emission of the atom, in particular the spectrum of the emitted radiation. Specifically, we find the appearance of two symmetric lateral peaks in the spectrum, not present in the case of a static mirror, due to the modulated environment. The two lateral peaks are separated from the central peak by the modulation frequency, and we discuss the possibility to observe them with actual experimental techniques of dynamical mirrors and atomic trapping. Our results indicate that a dynamical (i.e., time-modulated) environment can give new possibilities to control and manipulate also other radiative processes of two or more atoms or molecules nearby, for example their cooperative decay or the resonant energy transfer
Vacuum field correlations and three-body Casimir-Polder potential with one excited atom
The three-body Casimir-Polder potential between one excited and two
ground-state atoms is evaluated. A physical model based on the dressed field
correlations of vacuum fluctuations is used, generalizing a model previously
introduced for three ground-state atoms. Although the three-body potential with
one excited atom is already known in the literature, our model gives new
insights on the nature of non-additive Casimir-Polder forces with one or more
excited atoms.Comment: 9 page
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
Dynamical Casimir-Polder energy between an excited and a ground-state atom
We consider the Casimir-Polder interaction between two atoms, one in the
ground state and the other in its excited state. The interaction is
time-dependent for this system, because of the dynamical self-dressing and the
spontaneous decay of the excited atom. We calculate the dynamical
Casimir-Polder potential between the two atoms using an effective Hamiltonian
approach. The results obtained and their physical meaning are discussed and
compared with previous results based on a time-independent approach which uses
a non-normalizable dressed state for the excited atom.Comment: 11 page
Dynamical Casimir-Polder force between an excited atom and a conducting wall
We consider the dynamical atom-surface Casimir-Polder force in the nonequilibrium configuration of an atom near a perfectly conducting wall, initially prepared in an excited state with the field in its vacuum state. We evaluate the time-dependent Casimir-Polder force on the atom and find that it shows an oscillatory behavior from attractive to repulsive both in time and in space. We also investigate the asymptotic behavior in time of the dynamical force and of related local field quantities, showing that the static value of the force, as obtained by a time-independent approach, is recovered for times much longer than the time scale of the atomic self-dressing but shorter than the atomic decay time. We then discuss the evolution of global quantities such as atomic and field energies and their asymptotic behavior. We also compare our results for the dynamical force on the excited atom with analogous results recently obtained for an initially bare ground-state atom. We show that new relevant features are obtained in the case of an initially excited atom, for example, much larger values of the dynamical force with respect to the static one, allowing for an easier way to single out and observe the dynamical Casimir-Polder effect
Effective hamiltonians in nonrelativistic quantum electrodynamics
In this paper, we consider some second-order effective Hamiltonians describing the interaction of the quantum electromagnetic field with atoms or molecules in the nonrelativistic limit. Our procedure is valid only for off-energy-shell processes, specifically virtual processes such as those relevant for ground-state energy shifts and dispersion van der Waals and Casimir-Polder interactions, while on-energy-shell processes are excluded. These effective Hamiltonians allow for a considerable simplification of the calculation of radiative energy shifts, dispersion, and Casimir-Polder inter-actions, including in the presence of boundary conditions. They can also provide clear physical insights into the processes involved. We clarify that the form of the effective Hamiltonian depends on the field states considered, and consequently different expressions can be obtained, each of them with a well-defined range of validity and possible applications. We also apply our results to some specific cases, mainly the Lamb shift, the Casimir-Polder atom-surface interaction, and the dispersion interactions between atoms, molecules, or, in general, polarizable bodies
Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms
In this paper we discuss and review several aspects of the effect of boundary
conditions and structured environments on dispersion and resonance interactions
involving atoms or molecules, as well as on vacuum field fluctuations. We first
consider the case of a perfect mirror, which is free to move around an
equilibrium position and whose mechanical degrees of freedom are treated
quantum mechanically. We investigate how the quantum fluctuations of the
mirror's position affect vacuum field fluctuations for both a one-dimensional
scalar and electromagnetic field, showing that the effect is particularly
significant in the proximity of the moving mirror. This result can be also
relevant for possible gravitational effects, since the field energy density
couples to gravity. We stress that this interaction-induced modification of the
vacuum field fluctuations can be probed through the Casimir-Polder interaction
with a polarizable body, thus allowing to detect the effect of the mirror's
quantum position fluctuations. We then consider the effect of an environment
such as an isotropic photonic crystal or a metallic waveguide, on the resonance
interaction between two entangled identical atoms, one excited and the other in
the ground state. We discuss the strong dependence of the resonance interaction
with the relative position of the atomic transition frequency with the gap of
the photonic crystal in the former case, and with the cut-off frequency of
waveguide in the latter.Comment: 8 pages, 2 figures, Proceedings of the Eighth International Workshop
DICE 2016 Spacetime - Matter - Quantum Mechanic
Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect
We discuss different physical effects related to the uniform acceleration of
atoms in vacuum, in the framework of quantum electrodynamics. We first
investigate the van der Waals/Casimir-Polder dispersion and resonance
interactions between two uniformly accelerated atoms in vacuum. We show that
the atomic acceleration significantly affects the van der Waals force, yielding
a different scaling of the interaction with the interatomic distance and an
explicit time dependence of the interaction energy. We argue how these results
could allow for an indirect detection of the Unruh effect through dispersion
interactions between atoms. We then consider the resonance interaction between
two accelerated atoms, prepared in a correlated Bell-type state, and
interacting with the electromagnetic field in the vacuum state, separating
vacuum fluctuations and radiation reaction contributions, both in the
free-space and in the presence of a perfectly reflecting plate. We show that
nonthermal effects of acceleration manifest in the resonance interaction,
yielding a change of the distance dependence of the resonance interaction
energy. This suggests that the equivalence between temperature and acceleration
does not apply to all radiative properties of accelerated atoms. To further
explore this aspect, we evaluate the resonance interaction between two atoms in
non inertial motion in the coaccelerated (Rindler) frame and show that in this
case the assumption of an Unruh temperature for the field is not required for a
complete equivalence of locally inertial and coaccelerated points of views.Comment: 8 pages, Proceedings of the Eighth International Workshop DICE 2016
Spacetime - Matter - Quantum Mechanic
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