The Casimir effect is a well-known macroscopic consequence of quantum vacuum fluctuations, but whereas the static effect (Casimir force) has long been observed experimentally, the dynamic Casimir effect is up to now undetected. From an experimental viewpoint a possible detection would imply the vibration of a mirror at gigahertz frequencies. Mechanical motions at such frequencies turn out to be technically unfeasible. Here we present a different experimental scheme where mechanical motions are avoided, and the results of laboratory tests showing that the scheme is practically feasible. We think that at present this approach gives the only possibility of detecting this phenomenon. PACS numbers: 12.20.Fv, 42.50.Dv, For any quantum field, the vacuum is defined as its ground state. Differently than in the classic case, this ground state, due to the uncertainty principle, is not empty, but filled with field fluctuations around a zero mean value. Moreover this vacuum state depends on the field boundary conditions : if they change, there will be a correspondingly different vacuum (whose fluctuations will have a different wavelength spectrum). Thus a quantum vacuum state may be equivalent to real particles of a new vacuum after a change in boundary conditions.If we consider the electromagnetic field, the peculiar nature of the quantum vacuum has experimentally observable consequences in the realm of microscopic physics, such as natural widths of spectral lines, Lamb shift, anomalous magnetic moment of the electron and many more. It is perhaps even more striking that there exist also observable effects at a macroscopic level. The Casimir force (static Casimir effect [1,2]) is one of these macroscopic effects which has been observed experimentally. A dynamic Casimir effect is also predicted to occur when one boundary is accelerated in a nonuniform way, as for instance when a metal surface undergoes harmonic oscillations. In this case a number of virtual photons from the vacuum are converted into real photons ("Casimir radiation"), while the moving metal surface loses energy [3,4,5].It is worth notice that, whereas the static Casimir effect has been observed by several experiments [6], the Casimir radiation is to date unobserved, in spite of the abundant theoretical work done in this field [7,8,9,10,11] (see [8] for a historical review and a bibliography of the relevant studies). We argue that this lack of experimental activity stems from the rooted idea of using mechanical oscillations. We shall show that this is unfeasible with present-day techniques.Here we shall present a new experimental approach where an effective motion is generated by the excitation of a plasma in a semiconductor. In terms of power this effective motion is much more convenient than a mechanical motion, since in a metal mirror only the conduction electrons reflect the electromagnetic waves, whereas a great amount of power would be wasted in the acceleration of the much heavier nuclei. Some authors [12,13,14] have made use of our idea in order to cons...

We study the proximity effect within a junction made of an unconventional superconductor (US) and a ferromagnet (F) in the clean limit with high barrier transparency. Superconductivity in the US side is described by an extended Hubbard model with intersite attractive interaction, while metallic ferromagnetism in the F side is assumed to be originated by a relative change in the bandwidths of electrons with opposite spin. The effect of this mass-split mechanism is analyzed in conjunction with the usual Stoner-like one, where one band is rigidly shifted with respect to the other, due to the presence of a constant exchange field. Starting from the numerical solution of the Bogoliubov-de Gennes equations, we show that the two above mentioned mechanisms for ferromagnetism lead to different features as concerns the formation at the interface of dominant and subdominant superconducting components, as well as their propagation in the ferromagnetic side. This considerably affects the opening of gaplike structures in the local density of states for majority and minority spin electrons, leading to distinct effects as one moves toward the half-metallic regime, where the density of the minority carriers becomes vanishing

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An approach to the calculation of FranckCondon factors in curvilinear coordinates is outlined. The approach is based on curvilinear normal coordinates, which allows for an easy extension of Duschinsky's transformation to the case of curvilinear coordinates, and on the power series expansion of the kinetic energy operator. Its usefulness in the case of molecules undergoing large displacements of their equilibrium nuclear configurations upon excitation is then demonstrated by an application to the vibrational structure of the photoelectron spectrum of ammonia, using an anharmonic potential only for the symmetric stretching and bending coordinates of the radical cation.

We study the dynamical, momentum dependent two-and four-spin response functions in doped and undoped 1D cuprates, as probed by resonant inelastic x-ray scattering, using an exact numerical diagonalization procedure. In the undoped t − J system the four-spin response vanishes at π, whereas the two-spin correlator is peaked around π/2, with generally larger spectral weight. Upon doping spectra tend to soften and broaden, with a transfer of spectral weight towards higher energy. However, the total spectral weight and average peak position of either response are only weakly affected by doping up to a concentration of 1/8. Only the two-spin response at π changes strongly, with a large reduction of spectral weight and enhancement of excitation energy. At other momenta the higher-energy, generic features of the magnetic response are robust against doping. It signals the presence of strong short-range antiferromagnetic correlations, even after doping mobile holes into the system. We expect this to hold also in higher dimensions.