386 research outputs found
Time-dependent Casimir-Polder forces and partially dressed states
A time-dependent Casimir-Polder force is shown to arise during the time
evolution of a partially dressed two-level atom. The partially dressed atom is
obtained by a rapid change of an atomic parameter such as its transition
frequency, due to the action of some external agent. The electromagnetic field
fluctuations around the atom, averaged over the solid angle for simplicity, are
calculated as a function of time, and it is shown that the interaction energy
with a second atom yields a dynamical Casimir-Polder potential between the two
atoms
Casimir-Polder forces between two accelerating atoms and the Unruh effect
The Casimir-Polder force between two atoms with equal uniform acceleration
and separated by a constant distance R is considered. We show that, in the
low-acceleration limit, while the near-zone R^{-6} behavior of the interatomic
interaction energy is not changed by the acceleration of the atoms, the
far-zone interaction energy decreases as R^{-5} instead of the well-known
R^{-7} behavior for inertial atoms. Possibility of an indirect detection of the
Unruh effect through measurements of the Casimir-Polder force between the two
accelerating atoms is also suggested. We also consider a heuristic model for
calculating the Casimir-Polder potential energy between the two atoms in the
high-acceleration limit.Comment: Contribution to the Proceedings of the QFEXT09 Conference, Norman,
Oklahoma, US
Field Fluctuations in a One-Dimensional Cavity with a Mobile Wall
We consider a scalar field in a one-dimensional cavity with a mobile wall.
The wall is assumed bounded by a harmonic potential and its mechanical degrees
of freedom are treated quantum mechanically. The possible motion of the wall
makes the cavity length variable, and yields a wall-field interaction and an
effective interaction among the modes of the cavity. We consider the ground
state of the coupled system and calculate the average number of virtual
excitations of the cavity modes induced by the wall-field interaction, as well
as the average value of the field energy density. We compare our results with
analogous quantities for a cavity with fixed walls, and show a correction to
the Casimir potential energy between the cavity walls. We also find a change of
the field energy density in the cavity, particularly relevant in the proximity
of the mobile wall, yielding a correction to the Casimir-Polder interaction
with a polarizable body placed inside the cavity. Similarities and differences
of our results with the dynamical Casimir effect are also discussed.Comment: 5 pages, 2 figure
van der Waals Interaction Energy Between Two Atoms Moving With Uniform Acceleration
We consider the interatomic van der Waals interaction energy between two
neutral ground-state atoms moving in the vacuum space with the same uniform
acceleration. We assume the acceleration orthogonal to their separation, so
that their mutual distance remains constant. Using a model for the van der
Waals dispersion interaction based on the interaction between the instantaneous
atomic dipole moments, which are induced and correlated by the zero-point field
fluctuations, we evaluate the interaction energy between the two accelerating
atoms in terms of quantities expressed in the laboratory reference frame. We
find that the dependence of the van der Waals interaction between the atoms
from the distance is different with respect to the case of atoms at rest, and
the relation of our results with the Unruh effect is discussed. We show that in
the near zone a new term proportional to adds to the usual
behavior, and in the far zone a term proportional to adds to the usual
behavior, making the interaction of a longer range. We also find that
the interaction energy is time-dependent, and the physical meaning of this
result is discussed. In particular, we find acceleration-dependent corrections
to the (far zone) and (near zone) proportional to
; this suggests that significant changes to the van der Waals
interaction between the atoms could be obtained if sufficiently long times are
taken, without necessity of the extremely high accelerations required by other
known manifestations of the Unruh effect.Comment: 9 page
Spatial correlations of vacuum fluctuations and the Casimir-Polder potential
We calculate the Casimir-Polder intermolecular potential using an effective
Hamiltonian recently introduced. We show that the potential can be expressed in
terms of the dynamical polarizabilities of the two atoms and the equal-time
spatial correlation of the electric field in the vacuum state. This gives
support to an interesting physical model recently proposed in the literature,
where the potential is obtained from the classical interaction between the
instantaneous atomic dipoles induced and correlated by the vacuum fluctuations.
Also, the results obtained suggest a more general validity of this intuitive
model, for example when external boundaries or thermal fields are present.Comment: 7 page
Thermal and non-thermal signatures of the Unruh effect in Casimir-Polder forces
We show that Casimir-Polder forces between two relativistic uniformly
accelerated atoms exhibit a transition from the short distance thermal-like
behavior predicted by the Unruh effect, to a long distance non-thermal
behavior, associated with the breakdown of a local inertial description of the
system. This phenomenology extends the Unruh thermal response detected by a
single accelerated observer to an accelerated spatially extended system of two
particles, and we identify the characteristic length scale for this crossover
with the inverse of the proper acceleration of the two atoms. Our results are
derived separating at fourth order in perturbation theory the contributions of
vacuum fluctuations and radiation reaction field to the Casimir-Polder
interaction between two atoms moving in two generic stationary trajectories
separated by a constant distance, and linearly coupled to a scalar field. The
field can be assumed in its vacuum state or at finite temperature, resulting in
a general method for the computation of Casimir-Polder forces in stationary
regimes.Comment: 6 pages, 1 figure. Revised versio
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
Resonance interaction energy between two entangled atoms in a photonic bandgap environment
We consider the resonance interaction energy between two identical entangled
atoms, where one is in the excited state and the other in the ground state.
They interact with the quantum electromagnetic field in the vacuum state and
are placed in a photonic-bandgap environment with a dispersion relation
quadratic near the gap edge and linear for low frequencies, while the atomic
transition frequency is assumed to be inside the photonic gap and near its
lower edge. This problem is strictly related to the coherent resonant energy
transfer between atoms in external environments. The analysis involves both an
isotropic three-dimensional model and the one-dimensional case. The resonance
interaction asymptotically decays faster with distance compared to the
free-space case, specifically as compared to the free-space
dependence in the three-dimensional case, and as compared to the
oscillatory dependence in free space for the one-dimensional case. Nonetheless,
the interaction energy remains significant and much stronger than dispersion
interactions between atoms. On the other hand, spontaneous emission is strongly
suppressed by the environment and the correlated state is thus preserved by the
spontaneous-decay decoherence effects. We conclude that our configuration is
suitable for observing the elusive quantum resonance interaction between
entangled atoms.Comment: 12 pages, 3 figure
Control of spontaneous emission of a single quantum emitter through a time-modulated photonic-band-gap environment
We consider the spontaneous emission of a two-level quantum emitter, such as
an atom or a quantum dot, in a modulated time-dependent environment with a
photonic band gap. An example of such an environment is a dynamical photonic
crystal or any other environment with a bandgap whose properties are modulated
in time, in the effective mass approximation. After introducing our model of
dynamical photonic crystal, we show that it allows new possibilities to control
and tailor the physical features of the emitted radiation, specifically its
frequency spectrum. In the weak coupling limit and in an adiabatic case, we
obtain the emitted spectrum and we show the appearance of two lateral peaks due
to the presence of the modulated environment, separated from the central peak
by the modulation frequency. We show that the two side peaks are not symmetric
in height, and that their height ratio can be exploited to investigate the
density of states of the environment. Our results show that a dynamical
environment can give further possibilities to modify the spontaneous emission
features, such as its spectrum and emission rate, with respect to a static one.
Observability of the phenomena we obtain is discussed, as well as relevance for
tailoring and engineering radiative processes.Comment: 9 pages, 3 figure
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