Search results for "Quantum Fluctuation"

Towards quantum phase slip based standard of electric current

2019

An accurate standard of electric current is a long-standing challenge of modern metrology. It has been predicted that a superconducting nanowire in the regime of quantum fluctuations can be considered as the dynamic equivalent of a chain of conventional Josephson junctions. In full analogy with the quantum standard of electric voltage based on the Josephson effect, the quantum phase slip phenomenon in ultrathin superconducting nanowires could be used for building the quantum standard of electric current. This work presents advances toward this ultimate goal.

Electromagnetic field fluctuations near a dielectric half-space and appearance of surface divergences in the ideal conductor limit

2012

The electromagnetic field fluctuations in the vacuum state are considered in the region external to a half-space filled with a homogeneous non-dissipative dielectric. We discuss the appropriate limits to a real and an ideal metal, focusing on the renormalized field fluctuations (equivalent to energy densities) in the proximity of the dielectric-vacuum interface. We show that, whereas in presence of a real conductor the renormalized field fluctuations are finite in any point of space, surface divergences appear at the interface in the ideal conductor limit. The main features of such divergences are discussed in detail. We point out that the behavior of field fluctuations close to the interfa…

Causality and Localization Operators

2005

The evolution of the expectation values of one and two points scalar field operators and of positive localization operators, generated by an istantaneous point source is non local. Non locality is attributed either to zero point vacuum fluctuations, or to non local operations or to the microcausality principle being no satisfied.

Lamb shift of a uniformly accelerated hydrogen atom in the presence of a conducting plate

2009

We investigate the effects of acceleration on the energy-level shifts of a hydrogen atom interacting with the electromagnetic field and in the presence of an infinite perfectly conducting plate. We consider the contributions of vacuum fluctuations and of the radiation reaction field to the Lamb shift, and we discuss their dependence from the acceleration of the atom. We show that, because of the presence of the boundary, both vacuum field fluctuations and radiation reaction field contributions are affected by atomic acceleration. In particular, the effect of the vacuum field fluctuations on the energy-level shifts is not equivalent to that of a thermal field. We also discuss the dependence …

Dielectric relaxation and conductivity in ferroelectric perovskites

1996

Abstract Ferroelectric ABO3 perovskites are usually well known for their high dielectric susceptibility. Under selected impurity substitutions their conductivity may be strongly increased. The interaction between electronic conductivity and lattice polarizability may take place over different length scales. At high temperatures (T > 300 K), this interaction length is macroscopic leading to space charges. At low temperatures (T < 50 K), the polaronic interaction is restricted to a few unit cells. In the special case of SrTiO3, these polaronic excitons are sensitive to the quantum fluctuations which lead to the new concept of quantum polarons.

Dynamical mean-field theory versus second-order perturbation theory for the trapped two-dimensional Hubbard antiferromagnet

2011

In recent literature on trapped ultracold atomic gases, calculations for two-dimensional (2D) systems are often done within the dynamical mean-field theory (DMFT) approximation. In this paper, we compare DMFT to a fully 2D, self-consistent second-order perturbation theory for weak interactions in a repulsive Fermi-Hubbard model. We investigate the role of quantum and of spatial fluctuations when the system is in the antiferromagnetic phase, and find that, while quantum fluctuations decrease drastically the order parameter and critical temperatures, spatial fluctuations only play a noticeable role when the system undergoes a phase transition, or at phase boundaries in the trap. We conclude f…

Dynamical atom-wall Casimir-Polder forces

2013

Fluctuations of the Casimir-Polder force between an atom and a conducting wall

2007

We consider the quantum fluctuations of the Casimir-Polder force between a neutral atom and a perfectly conducting wall in the ground state of the system. In order to obtain the atom-wall force fluctuation we first define an operator directly associated to the force experienced by the atom considered as a polarizable body in an electromagnetic field, and we use a time-averaged force operator in order to avoid ultraviolet divergences appearing in the fluctuation of the force. This time-averaged force operator takes into account that any measurement involves a finite time. We also calculate the Casimir-Polder force fluctuation for an atom between two conducting walls. Experimental observabili…

Resonance Dipole-Dipole Interaction Between Two Accelerated Atoms in the Presence of a Reflecting Plane Boundary

2018

We study the resonant dipole-dipole interaction energy between two uniformly accelerated identical atoms, one excited and the other in the ground state, prepared in a correlated {\em Bell-type} state, and interacting with the scalar field or the electromagnetic field nearby a perfectly reflecting plate. We suppose the two atoms moving with the same uniform acceleration, parallel to the plane boundary, and that their separation is constant during the motion. We separate the contributions of vacuum fluctuations and radiation reaction field to the resonance energy shift of the two-atom system, and show that Unruh thermal fluctuations do not affect the resonance interaction, which is exclusivel…

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…