Macroscopic Coherence for a Trapped Electron

We investigate the possibility of generating quantum macroscopic coherence phenomena by means of relativistic effects on a trapped electron.Comment: 6 pages, RevTex, accepted by Phys. Rev.

Measuring the Cyclotron State of a Trapped Electron

We propose the cyclotron state retrieval of an electron trapped in a Penning trap by using different measurement schemes based on suitable modifications of the applied electromagnetic fields and exploiting the axial degree of freedom as a probe. A test for matter-antimatter symmetry of the quantum state is proposed.Comment: 8 pages, RevTex, 2 figures available from the authors, accepted by Phys. Rev.

Emery vs. Hubbard model for cuprate superconductors: a Composite Operator Method study

Within the Composite Operator Method (COM), we report the solution of the Emery model (also known as p-d or three band model), which is relevant for the cuprate high-Tc superconduc- tors. We also discuss the relevance of the often-neglected direct oxygen-oxygen hopping for a more accurate, sometimes unique, description of this class of materials. The benchmark of the solution is performed by comparing our results with the available quantum Monte Carlo ones. Both single- particle and thermodynamic properties of the model are studied in detail. Our solution features a metal-insulator transition at half filling. The resulting metal-insulator phase diagram agrees qual- itatively very well with the one obtained within Dynamical Mean-Field Theory. We discuss the type of transition (Mott-Hubbard (MH) or charge-transfer (CT)) for the microscopic (ab-initio) parameter range relevant for cuprates getting, as expected a CT type. The emerging single-particle scenario clearly suggests a very close relation between the relevant sub-bands of the three- (Emery) and the single- band (Hubbard) models, thus providing an independent and non-perturbative proof of the validity of the mapping between the two models for the model parameters optimal to describe cuprates. Such a result confirms the emergence of the Zhang-Rice scenario, which has been recently questioned. We also report the behavior of the specific heat and of the entropy as functions of the temperature on varying the model parameters as these quantities, more than any other, depend on and, consequently, reveal the most relevant energy scales of the system.Comment: 20 pages, 19 figure

Different realizations of tomographic principle in quantum state measurement

We establish a general principle for the tomographic approach to quantum state reconstruction, till now based on a simple rotation transformation in the phase space, which allows us to consider other types of transformations. Then, we will present different realizations of the principle in specific examples.Comment: 17 pages, Latex file, no figures, accepted by J. of Mod. Op

Optomechanical detection of weak forces

Optomechanical systems are often used for the measurement of weak forces. Feedback loops can be used in these systems for achieving noise reduction. Here we show that even though feedback is not able to improve the signal to noise ratio of the device in stationary conditions, it is possible to design a nonstationary strategy able to improve the sensitivity.Comment: 12 pages, 6 figures, contribution to the proceedings of the SPIE Conference on Fluctuations and Nois

Hijos del desarrollo de los mass media de los ochenta. Datos sociodemográficos de una investigación sobre los periodistas italianos.

Sin resume

Stationary entanglement between macroscopic mechanical oscillators

We show that the optomechanical coupling between an optical cavity mode and the two movable cavity end mirrors is able to entangle two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present technology.Comment: 9 pages, 4 figures. To be published on the Special Issue of EPJD "Quantum fluctuations and coherence in optical and atomic structures", edited by J. Eschner, A. Gatti, A. Maitre and G. Morigi v3: an error in a parameter definition correcte

Continuous variable encoding by ponderomotive interaction

Recently it has been proposed to construct quantum error-correcting codes that embed a finite-dimensional Hilbert space in the infinite-dimensional Hilbert space of a system described by continuous quantum variables [D. Gottesman et al., Phys. Rev. A 64, 012310 (2001)]. The main difficulty of this continuous variable encoding relies on the physical generation of the quantum codewords. We show that ponderomotive interaction suffices to this end. As a matter of fact, this kind of interaction between a system and a meter causes a frequency change on the meter proportional to the position quadrature of the system. Then, a phase measurement of the meter leaves the system in an eigenstate of the stabilizer generators, provided that system and meter's initial states are suitably prepared. Here we show how to implement this interaction using trapped ions, and how the encoding can be performed on their motional degrees of freedom. The robustness of the codewords with respect to the various experimental imperfections is then analyzed.Comment: Revised version - 9 pages, 4 figure