Salvatore Spagnolo

Non-Hermitian Hamiltonian for a modulated Jaynes-Cummings model with PT symmetry

We consider a two-level system such as a two-level atom, interacting with a cavity field mode in the rotating wave approximation, when the atomic transition frequency or the field mode frequency is periodically driven in time. We show that in both cases, for an appropriate choice of the modulation parameters, the state amplitudes in a generic

Temperature dependence of the magnetic Casimir-Polder interaction

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Casimir-Polder interatomic potential between two atoms at finite temperature and in the presence of boundary conditions

{-}excitation subspace obey the same equations of motion that can be obtained from a \emph{static} non-Hermitian Jaynes-Cummings Hamiltonian with

Field fluctuations near a conducting plate and Casimir-Polder forces in the presence of boundary conditions

{\mathcal PT}

Nonthermal effects of acceleration in the resonance interaction between two uniformly accelerated atoms

symmetry, that is with an imaginary coupling constant. This gives further support to recent results showing the possible physical interest of

Optomechanical Rydberg-atom excitation via dynamic Casimir-Polder coupling.

{\mathcal PT}

Energy-level shifts of a uniformly accelerated atom between two reflecting plates

symmetric non-Hermitian Hamiltonians. We also generalize the well-known diagonalization of the Jaynes-Cummings Hamiltonian to the non-Hermitian case in terms of pseudo-bosons and pseudo-fermions, and discuss relevant mathematical and physical aspects.

Casimir-Polder forces, boundary conditions and fluctuations

We analyze the magnetic dipole contribution to atom-surface dispersion forces. Unlike its electrical counterpart, it involves small transition frequencies that are comparable to thermal energy scales. A significant temperature dependence is found near surfaces with a nonzero dc conductivity, leading to a strong suppression of the dispersion force at T>0. We use thermal response theory for the surface material and discuss both normal metals and superconductors. The asymptotes of the free energy of interaction and of the entropy are calculated analytically over a large range of distances. Near a superconductor, the onset of dissipation at the phase transition strongly changes the interaction, including a discontinuous entropy. We discuss the similarities with the Casimir interaction between two surfaces and suggest that precision measurements of the atom-surface interaction may shed light upon open questions around the temperature dependence of dispersion forces between lossy media.

Coordinate representation for non-Hermitian position and momentum operators

We evaluate the Casimir-Polder potential between two atoms in the presence of an infinite perfectly conducting plate and at nonzero temperature. In order to calculate the potential, we use a method based on equal-time spatial correlations of the electric field, already used to evaluate the effect of boundary conditions on interatomic potentials. This method also gives a transparent physical picture of the role of a finite temperature and boundary conditions on the Casimir-Polder potential. We obtain an analytical expression of the potential both in the near and far zones, and consider several limiting cases of interest, according to the values of the parameters involved, such as atom-atom distance, atoms-wall distance, and temperature.

Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect

We consider vacuum fluctuations of the quantum electromagnetic field in the presence of an infinite and perfectly conducting plate. We evaluate how the change of vacuum fluctuations due to the plate modifies the Casimir-Polder potential between two atoms placed near the plate. We use two different methods to evaluate the Casimir-Polder potential in the presence of the plate. They also give insights on the role of boundary conditions in the Casimir-Polder interatomic potential, as well as indications for possible generalizations to more complicated boundary conditions.