Diego A. R. Dalvit

Terahertz Metamaterials for Linear Polarization Conversion and Anomalous Refraction

Converting Polarization The conversion of a light signal from one polarization direction to another plays an important role in communication and metrology. The components that are presently used for polarization conversion, however, tend to be relatively large, which is an issue that can make it difficult to integrate with chip-scale optoelectronic circuits. Grady et al. (p. 1304, published online 16 May) used a metasurfaces approach involving a designed array of cut wires to manipulate the polarization state of the propagating terahertz signals. Proper design of the device structure allowed for the control of the polarization conversion state for both reflected and transmitted light over a broad frequency range. A metasurface-based design is used for polarization conversion in the terahertz regime. Polarization is one of the basic properties of electromagnetic waves conveying valuable information in signal transmission and sensitive measurements. Conventional methods for advanced polarization control impose demanding requirements on material properties and attain only limited performance. We demonstrated ultrathin, broadband, and highly efficient metamaterial-based terahertz polarization converters that are capable of rotating a linear polarization state into its orthogonal one. On the basis of these results, we created metamaterial structures capable of realizing near-perfect anomalous refraction. Our work opens new opportunities for creating high-performance photonic devices and enables emergent metamaterial functionalities for applications in the technologically difficult terahertz-frequency regime.

Observation of the thermal Casimir force

A thermal Casimir force—an attraction between two metal surfaces caused by thermal, rather than quantum, fluctuations in the electromagnetic field—has now been identified experimentally between a flat and a spherical gold plate.

Materials perspective on Casimir and van der Waals interactions

Interactions induced by electromagnetic fluctuations, such as van der Waals and Casimir forces, are of universal nature present at any length scale between any types of systems with finite dimensions. Such interactions are important not only for the fundamental science of materials behavior, but also for the design and improvement of micro- and nano-structured devices. In the past decade, many new materials have become available, which has stimulated the need of understanding their dispersive interactions. The field of van der Waals and Casimir forces has experienced an impetus in terms of developing novel theoretical and computational methods to provide new insights in related phenomena. The understanding of such forces has far reaching consequences as it bridges concepts in materials, atomic and molecular physics, condensed matter physics, high energy physics, chemistry and biology. In this review, we summarize major breakthroughs and emphasize the common origin of van der Waals and Casimir interactions. We examine progress related to novel ab initio modeling approaches and their application in various systems, interactions in materials with Dirac-like spectra, force manipulations through nontrivial boundary conditions, and applications of van der Waals forces in organic and biological matter. The outlook of the review is to give the scientific community a materials perspective of van der Waals and Casimir phenomena and stimulate the development of experimental techniques and applications.

Casimir-Lifshitz Theory and Metamaterials

Based on a generalization of the Lifshiftz theory, we calculate Casimir forces involving magnetodielectric and possibly anisotropic metamaterials, focusing on the possibility of repulsive forces. It is found that Casimir repulsion decreases with magnetic dissipation, and even a small Drude background in metallic-based metamaterials acts to make attractive a Casimir force that would otherwise be predicted to be repulsive. The sign of the force also depends sensitively on the degree of optical anisotropy of the metamaterial and on the form of the frequency dependency of the magnetic response.

Decoherence and the Loschmidt Echo

Decoherence causes entropy increase that can be quantified using, e.g., the purity sigma=Trrho(2). When the Hamiltonian of a quantum system is perturbed, its sensitivity to such perturbation can be measured by the Loschmidt echo M(t). It is given by the squared overlap between the perturbed and unperturbed state. We describe the relation between the temporal behavior of sigma(t) and the average Mmacr;(t). In this way we show that the decay of the Loschmidt echo can be analyzed using tools developed in the study of decoherence. In particular, for systems with a classically chaotic Hamiltonian the decay of sigma and Mmacr; has a regime where it is dominated by the Lyapunov exponents.

Surface Contact Potential Patches and Casimir Force Measurements

We present calculations of contact potential surface patch effects that simplify previous treatments. It is shown that, because of the linearity of Laplaces equation, the presence of patch potentials does not affect an electrostatic calibration of a two-plate Casimir measurement apparatus. Using models that include long-range variations in the contact potential across the plate surfaces, a number of experimental observations can be reproduced and explained. For these models, numerical calculations show that if a voltage is applied between the plates which minimizes the force, a residual electrostatic force persists, and that the minimizing potential varies with distance. The residual force can be described by a fit to a simple two-parameter function involving the minimizing potential and its variation with distance. We show the origin of this residual force by use of a simple parallel capacitor model. Finally, the implications of a residual force that varies in a manner different from

Anomalies in electrostatic calibrations for the measurement of the Casimir force in a sphere-plane geometry

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Measurement of the Short-Range Attractive Force between Ge Plates Using a Torsion Balance

on the accuracy of previous Casimir measurements is discussed.

Metasurface Broadband Solar Absorber

Dipartimento di Fisica “Galileo Galilei”, Universit`a di Padova, Via Marzolo 8, Padova 35131, Italy(Dated: December 1, 2008)We have performed precision electrostatic calibrations in the sphere-plane geometry, and observedanomalous behavior. Namely, the scaling exponent of the electrostatic signal with distance was foundto be smaller than expected on the basis of the pure Coulombian contribution, and the residualpotential found to be distance dependent. We argue that these findings affect the accuracy of theelectrostatic calibrations and invite reanalysis of previous determinations of the Casimir force.

Resonant photon creation in a three-dimensional oscillating cavity

We have measured the short-range attractive force between crystalline Ge plates, and found contributions from both the Casimir force and an electrical force possibly generated by surface patch potentials. Using a model of surface patch effects that generates an additional force due to a distance dependence of the apparent contact potential, the electrical force was parametrized using data at distances where the Casimir force is relatively small. Extrapolating this model, to provide a correction to the measured force at distances less than 5 microm, shows a residual force that is in agreement, within experimental uncertainty, with five models that have been used to calculate the Casimir force.