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 $R^{-5}$ adds to the usual $R^{-6}$ behavior, and in the far zone a term proportional to $R^{-6}$ adds to the usual $R^{-7}$ 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 $R^{-7}$ (far zone) and $R^{-6}$ (near zone) proportional to $a^2t^2/c^2$; 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

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 $1/r^2$ compared to the $1/r$ free-space dependence in the three-dimensional case, and as $1/r$ 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

Resonance interaction energy between two accelerated identical atoms in a coaccelerated frame and the Unruh effect

We investigate the resonance interaction energy between two uniformly accelerated identical atoms, interacting with the scalar field or the electromagnetic field in the vacuum state, in the reference frame coaccelerating with the atoms. We assume that one atom is excited and the other in the ground state, and that they are prepared in their correlated symmetric or antisymmetric state. Using perturbation theory, we separate, at the second order in the atom-field coupling, the contributions of vacuum fluctuations and radiation reaction field to the energy shift of the interacting system. We show that only the radiation reaction term contributes to the resonance interaction between the two atoms, while Unruh thermal fluctuations, related to the vacuum fluctuations contribution, do not affect the resonance interatomic interaction. We also show that the resonance interaction between two uniformly accelerated atoms, recently investigated in the comoving (locally inertial) frame, can be recovered in the coaccelerated frame, without the additional assumption of the Fulling-Davies-Unruh temperature for the quantum fields (as necessary for the Lamb-shift, for example). This indicates, in the case considered, the equivalence between the coaccelerated frame and the locally inertial frame.Comment: 9 page

New Trends in Quantum Electrodynamics

Quantum electrodynamics is one of the most successful physical theories, and its predictions agree with experimental results with exceptional accuracy. Nowadays, after several decades since its introduction, quantum electrodynamics is still a very active research field from both the theoretical and experimental points of view. The aim of this Special Issue is to present recent relevant advances in quantum electrodynamics, both theoretical and experimental, and related aspects in quantum field theory and quantum optics

Van der Waals interactions between excited atoms in generic environments

We consider the the van der Waals force involving excited atoms in general environments, constituted by magnetodielectric bodies. We develop a dynamical approach studying the dynamics of the atoms and the field, mutually coupled. When only one atom is excited, our dynamical theory suggests that for large distances the van der Waals force acting on the ground-state atom is monotonic, while the force acting in the excited atom is spatially oscillating. We show how this latter force can be related to the known oscillating Casimir--Polder force on an excited atom near a (ground-state) body. Our force also reveals a population-induced dynamics: for times much larger that the atomic lifetime the atoms will decay to their ground-states leading to the van der Waals interaction between ground-state atoms.Comment: 19 pages, 4 figure

Dynamical Casimir-Polder interaction between a chiral molecule and a surface

We develop a dynamical approach to study the Casimir-Polder force between a initially bare molecule and a magnetodielectric body at finite temperature. Switching on the interaction between the molecule and the field at a particular time, we study the resulting temporal evolution of the Casimir-Polder interaction. The dynamical self-dressing of the molecule and its population-induced dynamics are accounted for and discussed. In particular, we find that the Casimir-Polder force between a chiral molecule and a perfect mirror oscillates in time with a frequency related to the molecular transition frequency, and converges to the static result for large times.Comment: 10 pages, 4 figure