Search results for "Fluctuations"

Nanoparticles at fluid interfaces.

2017

Nanoparticles at fluid interfaces are becoming a central topic in colloid science studies. Unlike in the case of colloids in suspensions, the description of the forces determining the physical behavior of colloids at interfaces still represents an outstanding problem in the modern theory of colloidal interactions. These forces regulate the formation of complex two-dimensional structures, which can be exploited in a number of applications of technological interest; optical devices, catalysis, molecular electronics or emulsions stabilization. From a fundamental viewpoint and typical for colloidal systems, nanoparticles and microparticles at interfaces are ideal experimental and theoretical mo…

Average Structure vs. Real Structure: Molecular Dynamics Studies of Silica

2003

The microscopic structure of a crystal and thermal fluctuations of the atoms constituting the crystal are intimately connected with the macroscopic elastic properties including mechanical stability. In some cases, however, the picture is more complex than that which is drawn in text books on solid state physics. (i) The instantaneous microscopic structure can deviate in a non-Gaussian way from the average structure even when domain disorder and/or crystal defects are absent. Quasi harmonic approximations may then turn out to be meaningless. (ii) The crystal is subject to external pressures that are sufficiently large in order to render the definition of elastic constants non unique. These t…

Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources

2014

We investigate the superconducting lifetime of long current-biased Josephson junctions, in the presence of Gaussian and non-Gaussian noise sources. In particular, we analyze the dynamics of a Josephson junction as a function of the noise signal intensity, for different values of the parameters of the system and external driving currents. We find that the mean lifetime of the superconductive state is characterized by nonmonotonic behavior as a function of noise intensity, driving frequency and junction length. We observe that these nonmonotonic behaviours are connected with the dynamics of the junction phase string during the switching towards the resistive state. An important role is played…

Dynamical atom-wall Casimir-Polder forces

2013

Electroluminescence TPCs at the thermal diffusion limit

2019

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM

Dispersion Interactions between Neutral Atoms and the Quantum Electrodynamical Vacuum

2018

Dispersion interactions are long-range interactions between neutral ground-state atoms or molecules, or polarizable bodies in general, due to their common interaction with the quantum electromagnetic field. They arise from the exchange of virtual photons between the atoms, and, in the case of three or more atoms, are not additive. In this review, after having introduced the relevant coupling schemes and effective Hamiltonians, as well as properties of the vacuum fluctuations, we~outline the main properties of dispersion interactions, both in the nonretarded (van der Waals) and retarded (Casimir--Polder) regime. We then discuss their deep relation with the existence of the vacuum fluctuation…

Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect

2017

We discuss different physical effects related to the uniform acceleration of atoms in vacuum, in the framework of quantum electrodynamics. We first investigate the van der Waals/Casimir-Polder dispersion and resonance interactions between two uniformly accelerated atoms in vacuum. We show that the atomic acceleration significantly affects the van der Waals force, yielding a different scaling of the interaction with the interatomic distance and an explicit time dependence of the interaction energy. We argue how these results could allow for an indirect detection of the Unruh effect through dispersion interactions between atoms. We then consider the resonance interaction between two accelerat…

Field fluctuations near a conducting plate and Casimir-Polder forces in the presence of boundary conditions

2006

We consider vacuum fluctuations of the quantum electromagnetic field in the presence of an infinite and perfectly conducting plate. We evaluate how the change of vacuum fluctuations due to the plate modifies the Casimir-Polder potential between two atoms placed near the plate. We use two different methods to evaluate the Casimir-Polder potential in the presence of the plate. They also give new insights on the role of boundary conditions in the Casimir-Polder interatomic potential, as well as indications for possible generalizations to more complicated boundary conditions.

Dynamical Casimir-Polder force between an atom and a conducting wall

2008

The time-dependent Casimir-Polder force arising during the time evolution of an initially bare two-level atom, interacting with the radiation field and placed near a perfectly conducting wall, is considered. Initially the electromagnetic field is supposed to be in the vacuum state and the atom in its ground state. The analytical expression of the force as a function of time and atom-wall distance, is evaluated from the the time-dependent atom-field interaction energy. Physical features and limits of validity of the results are discussed in detail.

Effect of boundaries on vacuum field fluctuations and radiation-mediated interactions between atoms

2017

In this paper we discuss and review several aspects of the effect of boundary conditions and structured environments on dispersion and resonance interactions involving atoms or molecules, as well as on vacuum field fluctuations. We first consider the case of a perfect mirror, which is free to move around an equilibrium position and whose mechanical degrees of freedom are treated quantum mechanically. We investigate how the quantum fluctuations of the mirror's position affect vacuum field fluctuations for both a one-dimensional scalar and electromagnetic field, showing that the effect is particularly significant in the proximity of the moving mirror. This result can be also relevant for poss…