arXiv subjects
Publications and source records attributed to B. Carazza.
We propose a phenomenological Hamiltonian for the interaction of neutral macroscopic bodies with the electromagnetic field. Subsequently we revisit the assumption according to which the retarded interactions between neutral macroscopic bodies can be obtained through an additive principle i.e. summing the volume elements defined by the macroscopic bodies.
This note looks at the possibility of a system of free particles presenting decoherence in the total momentum when tracing upon their relative momenta if we take into account a relativistic correction to the expression of the kinetic energy.
This article examines the decoherence of a macroscopic body using a simple model of the environment and following the evolution of the pure state for the whole system. We found that decoherence occurs for very general initial conditions and were able to confirm a number of widely accepted features of the process.
We examine the reduced density matrix of the centre of mass on position basis considering a one-dimensional system of $N$ non-interacting distinguishable particles in a infinitely deep square potential well. We find a class of pure states of the system for which the off-diagonal elements of the matrix above go to zero as $N$ increases. This property holds too for the state vectors which are factorized in the single particle wave functions. In this last case, if the average energy of each particle is less than a common bound, the diagonal elements are distributed according to the normal law with a mean square deviation which becomes smaller and smaller as $N$ increases towards infinity. Therefore when the state vectors are of the type considered we cannot experience spatial superpositions of the centre of mass and we may conclude that position is a preferred basis for the collective variable.
Position holds a very special role in understanding the classical behaviour of macroscopic bodies on the basis of quantum principles. This lead us to examine the localised states of a large condensed object in the context of a realistic model. Following the argument that an isolated macroscopic body is usually described by a linear superposition of low-lying energy eigenstates, it has been found that localised states of this type correspond to a nearly minimum-uncertainty state for the center of mass. An indication is also given of the dependence of the center of mass position spread on the number of constituent particles. This paper is not offered as an answer to the intriguing question of the preferred role played by the position basis, but will hopefully provide some contribution to the quantum modelling of multi-particle systems.
We present here a modified hydrodynamical model for the collective electronic excitations of spherical atomic clusters. The model is applied to the giant-dipole plasmon mode of the free fullerene molecule.