On the basis of a quantum microscopic approach we study the cooperative effects induced by the dipole-dipole interaction in an ensemble of pointlike impurity centers located near a charged perfectly conducting surface. We analyze the simultaneous influence of the modified spatial structure of field modes near the conductive surface and the electric field on the transition spectrum of an excited atom inside an ensemble and on the radiation trapping. We show that the electric field modifies the cooperative Lamb shift, as well as the character of sub- and super-radiant decay. We also demonstrate that electro-optical effects in the presence of a surface are essentially different in comparison with those in free space. The nonmonotonic behavior of electro-optical effects in the presence of a surface with increasing of the electric field has been shown.
We investigate theoretically nonmagnetic impurity scattering in a one-dimensional atomic topological superfluid in harmonic traps by solving self-consistently the microscopic Bogoliubov-de Gennes equation. In sharp contrast to topologically trivial Bardeen-Cooper-Schrieffer
s-wave superfluid, topological superfluid can host a midgap state that is bound to localized nonmagnetic impurity. For strong impurity scattering, the bound state becomes universal, with nearly zero energy and a wave function that closely follows the symmetry of that of Majorana fermions. We propose that the observation of such a universal bound state could be useful evidence for characterizing the topological nature of topological superfluids. Our prediction is applicable to an ultracold, resonantly interacting Fermi gas of
40K atoms with spin-orbit coupling confined in a two-dimensional optical lattice.
In CsCdBr3 the trivalent Rare-Earth (RE) ions substitute for the divalent Cd ions. For reasons of charge compensation and the specific crystal structure, RE centers of the form RE3+ - (Cd vacancy) - RE3+ are preferentially formed. These symmetric pair centers are very suitable for studying cooperative effects of RE ions. These include processes between the ions of the pair as well as processes between the coupled pair and the electronic excitations of the host lattice. Experiments will be shown and discussed on: (i) cross relaxation and up-conversion by direct ion-ion interaction; (ii) cooperative cross relaxation of the Pr3+ pairs with the host lattice; and (iii) cooperative vibronic emission of the Pr3+ pairs with high phonon progressions.