A nuclear structure model based on linear response theory (i.e., Random Phase Approximation) and which includes pairing correlations and anharmonicities (coupling with collective vibrations), has been implemented in such a way that it can be applied on the same footing to magic as well as open-shell nuclei. As applications, we have chosen to study the dipole excitations both in well-known, stable isotopes like $^{208}$Pb and $^{120}$Sn as well as in the neutron-rich, unstable $^{132}$Sn nucleus, by addressing in the latter case the question about the nature of the low-lying strength. Our results suggest that the model is reliable and predicts in all cases low-lying strength of non collective nature.Comment: 16 pages, 6 figures; submitted for publicatio

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We adopt a kinetic theory of polariton nonequilibrium Bose-Einstein condensation to describe the formation of off-diagonal long-range order. The theory accounts properly for the dominant role of quantum fluctuations in the condensate. In realistic situations with optical excitation at high energy, it predicts a significant depletion of the condensate caused by long-wavelength fluctuations. As a consequence, the one-body density matrix in space displays a partially suppressed long-range order and a pronounced dependence on the finite size of the system.

The Hartree-Fock-Popov theory of interacting Bose particles is developed, for modeling exciton-polaritons in semiconductor microcavities undergoing Bose-Einstein condensation. A self-consistent treatment of the linear exciton-photon coupling and of the exciton nonlinearity provides a thermal equilibrium description of the collective excitation spectrum, of the polariton energy shifts and of the phase diagram. Quantitative predictions support recent experimental findings.

Control of the wave function of confined microcavity polaritons is demonstrated experimentally and theoretically by means of tailored resonant optical excitation. Three dimensional confinement is achieved by etching mesas on top of the microcavity spacer layer. Resonant excitation with a continuous-wave laser locks the phase of the discrete polariton states to the phase of the laser. By tuning the energy and momentum of the laser, we achieve precise control of the momentum pattern of the polariton wave function. This is an efficient and direct way for quantum control of electronic excitations in a solid.Polaritons in semiconductor microcavities are hybrid quasiparticles consisting of a superposition of photons and excitons. Due to their photon component, polaritons are characterized by a quantum coherence length in the several micron range. Owing to their exciton content, they display sizeable interactions, both mutual and with other electronic degrees of freedom. These unique features have produced striking matter wave phenomena, such as Bose-Einstein condensation, 1,2 or parametric processes 3,4 able to generate entangled polariton states. 5,6 The key feature of polaritons with respect to confinement is their very small effective mass, which is about 10 5 times smaller than the free-electron mass. Hence, confinement within micrometer sized traps is sufficient to produce an atomlike spectrum with discrete energy levels. Recently, several paradigms for spatial confinement of polaritons in semiconductor devices have been established. 7-10 This opens the way to quantum devices in which polaritons can be used as a vector of quantum information. 11 Their electronic component can be accessed and controlled optically, through their photonic component. This holds promise for preparation of quantum states, which might then be transferred to longer lived elements of quantum storage ͑e.g., localized spins͒, or as a mechanism for mediating interactions between such elements over long distances, as proposed in Ref. 12. Precise control of the polariton wave function is then an essential requirement.In this Rapid Communication we demonstrate the manipulation of the wave function of confined zero-dimensional ͑0D͒ exciton polaritons under resonant optical excitation. The excited wave functions are monitored by collecting the coherent emission from the polariton traps. Control of the spatial and momentum probability distribution of the confined polaritons is achieved by tuning either the incidence angle or the energy of the excitation beam. Our results are supported by numerical simulations based on the coupled Gross-Pitaevskii equations for excitons and photons.The sample we used to carry out our studies consists of a single quantum well embedded in a planar microcavity with a pattern of differently sized round mesas on the spacer layer. 13 Patterning the cavity thickness results in a modulation of the photon resonance energy, which corresponds to a potential trap, with finite-energy barriers, able to confine polaritons. The con...