Su una rappresentazione piana dei complessi lineari

Sunto Studio della rappresentazione piana dei sistemi lineari di complessi lineari a una e due dimensioni secondo il metodo delMayor.     

A Generalization of Entanglement to Convex Operational Theories: Entanglement Relative to a Subspace of Observables

We define what it means for a state in a convex cone of states on a space of observables to be generalized-entangled relative to a subspace of the observables, in a general ordered linear spaces framework for operational theories. This extends the notion of ordinary entanglement in quantum information theory to a much more general framework. Some important special cases are described, in which the distinguished observables are subspaces of the observables of a quantum system, leading to results like the identification of generalized unentangled states with Lie-group-theoretic coherent states when the special observables form an irreducibly represented Lie algebra. Some open problems, including that of generalizing the semigroup of local operations with classical communication to the convex cones case, are discussed. PACS: 03.65.Ud.     

Dynamical suppression of 1/f noise processes in qubit systems

We investigate the capability of dynamical decoupling techniques to reduce decoherence from a realistic environment generating 1/f noise. The predominance of low frequency modes in the noise profile allows for decoherence scenarios where relatively slow control rates suffice for a drastic improvement. However, the actual figure of merit is very sensitive to the details of the dynamics, with decoupling performance which may deteriorate for non-Gaussian noise and/or high frequency working points. Our results are promising for robust solid-state qubits and beyond.     

Random decoupling schemes for quantum dynamical control and error suppression

We present a general control-theoretic framework for constructing and analyzing random decoupling schemes, applicable to quantum dynamical control of arbitrary finite-dimensional composite systems. The basic idea is to design the control propagator according to a random rather than deterministic path on a group. We characterize the performance of random decoupling protocols, and identify control scenarios where they can significantly weaken time scale requirements as compared to cyclic counterparts. Implications for reliable quantum computation are discussed.     

Observation of soft-modes in a single crystal of Rb2ZnBr4 by Raman scattering

The Raman spectra of an oriented single crystal of Rb₂ZnBr₄ shows three soft modes. One of them is interpreted as the amplitude mode of the incommensurate phase. The second one, seen well below the lock-in transition temperature appears as the phase mode. Moreover, an additional soft mode is observed between T=120 K and T=20 K, in the b(c, c)a scattering geometry. By extrapolation it is found that its frequency would vanish around T₃=140 K ± 10 K. This soft mode is likely to be related to a new phase transition.     

Dissipation,mass exchange and the microscopic time scale of heavy-ion collisions

The time scale provided by the nucleon exchange mechanism in heavy-ion reactions is employed to study kinetic energy damping. The experimental kinetic energy lost per nucleon exchanged in Kr- and Xe-induced reactions is observed to decrease linearly with the total kinetic energy loss. These results, which are consistent with energy dissipation and nucleon exchange occuring on a similar time scale, are compared with the predictions of a one-body dissipation mechanism and a diffusion model.