Entropic localization in non-unitary Newtonian gravity

The localizing properties and the entropy production of the Newtonian limit of a nonunitary version of fourth order gravity are analyzed. It is argued that pure highly unlocalized states of the center of mass motion of macroscopic bodies rapidly evolve into unlocalized ensembles of highly localized states. The localization time and the final entropy are estimated

Relativistic generalizations of gravity-induced localization models

Nonunitary versions of Newtonian gravity leading to wavefunction localization admit natural special-relativistic generalizations. They include the first consistent relativistic localization models. At variance with the unified model of localization and gravity, the purely localizing version requires negative energy fields, which however are less harmful than usual and can be used to build ultraviolet-finite theories.Comment: RevTex, 10 page

Quantum Computation using Decoherence-Free States of the Physical Operator Algebra

The states of the physical algebra, namely the algebra generated by the operators involved in encoding and processing qubits, are considered instead of those of the whole system-algebra. If the physical algebra commutes with the interaction Hamiltonian, and the system Hamiltonian is the sum of arbitrary terms either commuting with or belonging to the physical algebra, then its states are decoherence free. One of the considered examples shows that, for a uniform collective coupling to the environment, the smallest number of physical qubits encoding a decoherence free logical qubit is reduced from four to three.Comment: 16 pages, LATEX/REVTEX, expanded version to appear in Phys. Rev.