Fernando C. Lombardo

Decoherence during inflation: The Generation of classical inhomogeneities

We show how the quantum-to-classical transition of the cosmological fluctuations produced during inflation can be described by means of the influence functional and the master equation. We split the inflaton field into the system field (long-wavelength modes), and the environment, represented by its own short-wavelength modes. We compute the decoherence times for the system-field modes and compare them with the other time scales of the model. We present the renormalized stochastic Langevin equation for an homogeneous system field and then we analyze the influence of the environment on the power spectrum for some modes in the system.

Coarse graining and decoherence in quantum field theory

We consider a {lambda}{phi}{sup 4} theory in Minkowski spacetime. We compute a {open_quote}{open_quote}coarse-grained effective action{close_quote}{close_quote} by integrating out the field modes with a wavelength shorter than a critical value. From this effective action we obtain the evolution equation for the reduced density matrix (master equation). We compute the diffusion coefficients of this equation and analyze the decoherence induced on the long-wavelength modes. We generalize the results to the case of a conformally coupled scalar field in de Sitter spacetime. We show that the decoherence is effective as long as the critical wavelength is taken to be not shorter than the Hubble radius. {copyright} {ital 1996 The American Physical Society.}

Geometric phases in open systems : A model to study how they are corrected by decoherence

We calculate the geometric phase for an open system (spin-boson model) which interacts with an environment (ohmic or nonohmic) at arbitrary temperature. However there have been many assumptions about the time scale at which the geometric phase can be measured, there has been no reported observation of geometric phases for mixed states under nonunitary evolution yet. We study not only how they are corrected by the presence of the different type of environments but estimate the corresponding times at which decoherence becomes effective as well. These estimations should be taken into account when planning experimental setups to study the geometric phase in the nonunitary regime, particularly important for the application of fault-tolerant quantum computation.

The proximity force approximation for the Casimir energy as a derivative expansion

The proximity force approximation (PFA) has been widely used as a tool to evaluate the Casimir force between smooth objects at small distances. In spite of being intuitively easy to grasp, it is generally believed to be an uncontrolled approximation. Indeed, its validity has only been tested in particular examples, by confronting its predictions with the next to leading order (NTLO) correction extracted from numerical or analytical solutions obtained without using the PFA. In this article we show that the PFA and its NTLO correction may be derived within a single framework, as the first two terms in a derivative expansion. To that effect, we consider the Casimir energy for a vacuum scalar field with Dirichlet conditions on a smooth curved surface described by a function

Exact Casimir interaction between eccentric cylinders

\psi

Model for resonant photon creation in a cavity with time-dependent conductivity

in front of a plane. By regarding the Casimir energy as a functional of

Exact zero-point interaction energy between cylinders

\psi

Casimir force between eccentric cylinders

, we show that the PFA is the leading term in a derivative expansion of this functional. We also obtain the general form of corresponding NTLO correction, which involves two derivatives of

Energy-momentum tensor for scalar fields coupled to the dilaton in two dimensions

\psi

Decoherence induced by zero-point fluctuations in quantum Brownian motion

. We show, by evaluating this correction term for particular geometries, that it properly reproduces the known corrections to PFA obtained from exact evaluations of the energy.