We consider an atom in interaction with a massless scalar quantum field. We discuss the structure of the rate of variation of the atomic energy for an arbitrary stationary motion of the atom through the quantum vacuum. Our main intention is to identify and to analyze quantitatively the distinct contributions of vacuum fluctuations and radiation reaction to the spontaneous excitation of a uniformly accelerated atom in its ground state. This gives an understanding of the role of the different physical processes underlying the Unruh effect. The atom's evolution into equilibrium and the Einstein coefficients for spontaneous excitation and spontaneous emission are calculated.

We present a new research-based course on quantum mechanics in which the conceptual issues of quantum mechanics are taught at an introductory level. In the context of virtual laboratories, the students discover from the very beginning how quantum phenomena deviate from our classical everyday experience. The results of the evaluation of the course show that most of the students acquired appropriate quantum mechanical conceptions, and that many of the common misconceptions encountered in traditional instruction have been avoided.

We consider the influence of acceleration on the radiative energy shifts of atoms in Minkowski space. We study a two-level atom coupled to a scalar quantum field. Using a Heisenberg picture approach, we are able to separate the contributions of vacuum fluctuations and radiation reaction to the Lamb shift of the two-level atom. The resulting energy shifts for the special case of a uniformly accelerated atom are then compared with those of an atom at rest.

We consider the computation of the entanglement entropy in curved backgrounds with event horizons. We use a Hamiltonian approach to the problem and perform numerical computations on a spherical lattice of spacing a. We study the cosmological case and make explicit computations for the Friedmann-Robertson-Walker universe. Our results for a massless, minimally coupled scalar field can be summarized by S ent = 0.30r 2 H /a 2 , which resembles the flat space formula, although here the horizon radius, r H , is timedependent.

We study how the decay properties of particles are changed by acceleration. It is shown that under the influence of acceleration (1) the lifetime of particles is modified and (2) new processes (like the decay of the proton) become possible. This is illustrated by considering scalar models for the decay of muons, pions, and protons. We discuss the close conceptual relation between these processes and the Unruh effect.

We study the spontaneous de-excitation and excitation of accelerated atoms on arbitrary stationary trajectories ("generalized Unruh effect"). We consider the effects of vacuum fluctuations and radiation reaction separately. We show that radiation reaction is generally not altered by stationary acceleration, whereas the contribution of vacuum fluctuations differs for all stationary accelerated trajectories from its inertial value. Spontaneous excitation from the ground state occurs for all accelerated stationary trajectories and is therefore the "normal case". We furthermore show that the radiative energy shift ("Lamb shift") of a two-level atom is modified by acceleration for all stationary trajectories. Again only vacuum fluctuations give rise to the shift. Our results are illustrated for the special case of an atom in circular motion, which may be experimentally relevant.

We investigat,? the implicat,ions of the presence of Minkowski part,icles on the Rindler particle content in the accelerated frame as well as on the excitation and deexcitat,ion of an accelerated particle detector. To obtaiii localized statements, the field quantization is based on wave packets. For bosonic particles, nonempty Minkowski modes imply an amplification of the number of Kindler. particles in specific modes. The ilnrlerlying processes reflect a nonlocal pair strlicture: specific pairs of modes with trajectories of the wave packet maxima passing different Rindler wedges are correlated. An elementary object of quantum optics in noninertial situations is the accelerated detector. The richer structure of the physics of its excitation and deexcitation is studied in detail. In addition to the generalizations of the inert,ially known excitation and deexcitation processes thew are structurally new processes that are inertially forbidden. These processes reflect the nonlocal pair correlations.

No abstract