Measurement of the temperature dependence of quartz refractive indices

We present and discuss a technique to measure concurrently the temperature dependence of quartz refractive indices in the thermal range 25–300° C. The magnitude of both indices is found to decrease slightly with increasing temperature in the thermal range considered.     

Anomalous temperature dependence of the Casimir force for thin metal films

Within the framework of the Drude dispersive model, we predict an unusual nonmonotonic temperature dependence of the Casimir force for thin metal films. For certain conditions, this force decreases with temperature due to the decrease of the metallic conductivity, whereas the force increases at high temperatures due to the increase of the thermal radiation pressure. We consider the attraction of a film to: either (i) a bulk ideal metal with a planar boundary, or (ii) a bulk metal sphere (lens). The experimental observation of the predicted decreasing temperature dependence of the Casimir force can put an end to the long-standing discussion on the role of the electron relaxation in the Casimir effect.     

Atoms near magnetodielectric bodies: van der Waals energy and the Casimir-Polder force

Based on macroscopic QED in linear, causal media, a consistent theory for the Casimir-Polder force acting on an atom positioned near dispersing and absorbing magnetodielectric bodies is presented. The perturbative result for the van der Waals energy is shown to exhibit interesting new features in the presence of magnetodielectric bodies. To go beyond perturbation theory, we start with the center-of-mass equation of motion and derive a dynamical expression for the Casimir-Polder force acting on an atom prepared in an arbitrary electronic state. For a nondriven atom in the weak coupling regime, the force as a function of time is shown to be a superposition of force components that are related to the electronic density matrix elements at a chosen time. These force components depend on the position-dependent polarizability of the atom, which correctly accounts for the body-induced level shifts and broadenings.     

The dynamical Casimir-Polder force in relativistic atomic motion near the surface of a thick plate

The dynamical Casimir-Polder force between a neutral atom (in the ground state) and a thick plate in relativistic motion of the atom in the direction parallel to the surface has been calculated. The material properties have been considered in the framework of the oscillator model of the atom and the Drude dielectric function for a plate. The limiting cases of the nonrelativistic velocity and perfectly conducting material of the plate have been discussed. A complex dependence of the force on the velocity (energy), the distance, and the material properties of the surface has been found.     

Measurement of improved pressure dependence of superconducting transition temperature

We describe a technique for making electrical transport measurements in a diamond anvil cell at liquid helium temperature having in situ pressure measurement option, permitting accurate pressure determination at any low temperature during the resistance measurement scan. In general, for four-probe resistivity measurements on a polycrystalline sample, four fine gold wires are kept in contact with the sample with the help of the compression from the soft solid (usually alkali halides such as NaCl, KCl, etc.) acting as a pressure-transmitting medium. The actual pressure on the sample is underestimated if not measured from a ruby sphere placed adjacent to the sample and at that very low temperature. Here, we demonstrate the technique with a quasi-four-probe resistance measurement on an Fe-based superconductor in the temperature range 1.2–300 K and pressures up to 8 GPa to find an improved pressure dependence of the superconducting transition temperature.     

Casimir-Polder力对左手材料板附近的原子的动力学作用

本文研究了初始处于激发态的两能级原子在左手材料附近运动时Casimir-Polder力对原子动力学的影响. 左手材料有两个的作用: 一是在距离界面波长区域内提供了较强的Casimir-Polder共振力, 二是在这一范围原子的自发辐射受到抑制, 延长了作用时间. 这两种效应使得依靠原子自发辐射这一过程中的Casimir-Polder力能对原子的运动学产生影响, 并将一定初速度的原子排斥远离界面. 由于原子偶极矩的取向会影响Casimir-Polder力的性质, 因此对于某些初始条件(初速度和初始位置), 不同偶极矩取向的原子有不同的运动学结果, 会被吸引到界面或反射出去, 从而对具有不同偶极矩方向的原子进行筛选. 当然由于Casimir-Polder力很小, 能够反射的初速度也很小, 但是已经可以反抗极低温的热涨落, 我们的理论预估值约为15 μupK. 如果和其他约束手段同时作用, 便能对原子的动力学产生更为有利的控制.     

Angular momentum and temperature dependence of fission barriers with a realistic force

Angular distributions and excitation functions were measured for 30 2⁺ resonances in the³⁹K(p,p₀) and₃₉K(p, α⁰) reactions. Partial reduced widths have been extracted for three proton channels; the relative signs of the reduced width amplitudes for two of these channels were also determined. Reduced widths are generally consistent with a Gaussian distribution for the reduced width amplitudes, but the amplitudes themselves are not. These data represent the first measurement of correlation coefficients in an entrance channel and suggest that the large correlations previously observed in exit channels are generic features of this mass region.     

Isotopic dependence of the Casimir force

We calculate the dependence of the Casimir force on the isotopic composition of the interacting objects. This dependence arises from the subtle influence of the nuclear masses on the electronic properties of the bodies. We discuss the relevance of these results to current experiments utilizing the isoelectronic effect to search at very short separations for new weak forces suggested by various unification theories.     

Casimir-Polder interaction of excited media

The potential of long-range interaction between two dissimilar atoms, one of which is excited, drops as 1/R ₂ with the distance for the Casimir-Polder limit of large distances in comparison with the wave-length of atom transitions (E.A. Power and T. Thirunamachandran, Phys. Rev. A 51, 3660 (1995)). It is shown that such a dependence, obtained with the help of perturbation technique, results in a divergence for the interaction potential between an excited atom and a medium of dilute gas. We develop a nonperturbative method based upon quantum Green’s functions (Yu. Sherkunov, Phys. Rev. A 72, 052703 (2005)) to calculate the interaction potential for an excited atom and a ground-state atom embedded in a dielectric medium, taking into account the absorption of photons in the dielectric medium. The exponential suppression of the interaction between the atoms is demonstrated. The force acting on an excited atom near the interface of dilute gas medium is calculated. The result is no more divergent. The force between gas media in Casimir-Polder regime is calculated as well. The text was submitted by the author in English.     

Casimir-Polder forces in the presence of the cosmic photon heat bath

We study the effect of a photon background at finite temperature T on the Van der Waals interactions among neutral bodies. It turns out that the long-range Casimir-Polder force is unaffected for distances much less than T⁻¹ and strongly enhanced for distances much above T⁻¹.     

Casimir-Polder interaction of atoms with magnetodielectric bodies

A general theory of the Casimir-Polder interaction of single atoms with dispersing and absorbing magnetodielectric bodies is presented, which is based on QED in linear, causal media. Both ground-state and excited atoms are considered. Whereas the Casimir-Polder force acting on a ground-state atom can conveniently be derived from a perturbative calculation of the atom-field coupling energy, an atom in an excited state is subject to transient force components that can only be fully understood by a dynamical treatment based on the body-assisted vacuum Lorentz force. The results show that the Casimir-Polder force can be influenced by the body-induced broadening and shifting of atomic transitions — an effect that is not accounted for within lowest-order perturbation theory. The theory is used to study the Casimir-Polder force of a ground-state atom placed within a magnetodielectric multilayer system, with special emphasis on thick and thin plates as well as a planar cavity consisting of two thick plates. It is shown how the competing attractive and repulsive force components related to the electric and magnetic properties of the medium, respectively, can — for sufficiently strong magnetic properties — lead to the formation of potential walls and wells.     

On the shape dependence of the tangential Casimir force

The normal and tangential Casimir force for the rack gear is calculated numerically in the case of ideal boundary conditions for the electromagnetic field—perfect reflection on the boundaries. The resulting tangential force appears to be essentially shape-dependent. Relatively small shape variations lead to the essential changes in tangential force, whereas normal force remains almost unchanged.     

Angular dependence of the critical current density and the temperature scaling of the flux pinning force in YBCO thin film

In this paper, the critical current J_c(Θ) have been investigated as a function of magnetic-field angle Θ. Θ is the angle between the c-axis and the applied magnetic field direction. This investigation concerned three temperature values (60?K, 78?K and 81?K). The normalized pinning force f_p versus the normalized magnetic field h was also studied (f_p?=?F_p / F_pmax and h?=?H / H_max). The F_p expression was determined based on the Kramer model.The studied sample was a single crystal of YBaCuO thin film deposited by the ablation laser method on the surface (100) of a SrTiO₃ substrate.The results of this work show the existence of point core pinning of the normal centers in the low field regime and the occurrence of the flux creep in high field regime.     

Nonlocal properties of dynamical three-body Casimir-Polder forces

We consider the three-body Casimir-Polder interaction between three atoms during their dynamical self-dressing. We show that the time-dependent three-body Casimir-Polder interaction energy displays nonlocal features related to quantum properties of the electromagnetic field and to the nonlocality of spatial field correlations. We discuss the measurability of this intriguing phenomenon and its relation with the usual concept of stationary three-body forces.     

On the temperature dependence of quarkonium correlators

I discuss the temperature dependence of quarkonium correlators calculated in lattice QCD. I show that the dominant source of the temperature dependence comes from the zero-mode contribution, while the temperature dependence associated with the melting of bound states is quite small. I study the zero-mode contribution quantitatively for various quark masses and show that it is well described by a quasi-particle model with temperature-dependent heavy quark mass. As a byproduct, an estimate of the medium dependence of the heavy-quark mass is obtained.