Van der Waals interaction and spontaneous decay of an excited atom in a superlens-type geometry

Within the framework of macroscopic quantum electrodynamics, the resonant van der Waals potential experienced by an excited two-level atom near a planar magneto-electric two-layer system consisting of a slab of left-handed material and a perfect mirror is studied. It is shown that disregarding of material absorption leads to unphysical results, with divergent values for the potential away from the surface. Under appropriate conditions, the setup is found to feature a barrier near the surface which can be employed to levitate particles or used as a trapping or cooling mechanism. Finally, the problem of spontaneous decay [J. K\"{a}stel and M. Fleischhauer, Phys. Rev. A \textbf{68}, 011804(R) (2005)] is revisited. Disregarding of absorption is shown to drastically falsify the dependence on the atomic position of the decay rate.Comment: 10 Pages, 6 figure

Electromagnetic-field quantization and spontaneous decay in left-handed media

We present a quantization scheme for the electromagnetic field interacting with atomic systems in the presence of dispersing and absorbing magnetodielectric media, including left-handed material having negative real part of the refractive index. The theory is applied to the spontaneous decay of a two-level atom at the center of a spherical free-space cavity surrounded by magnetodielectric matter of overlapping band-gap zones. Results for both big and small cavities are presented, and the problem of local-field corrections within the real-cavity model is addressed.Comment: 15 pages, 5 figures, RevTe

Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating.ope

The revised Children's Communication Checklist-2 (CCC-R): factor structure and psychometric evaluation

Abstract: The Children's Communication Checklist-2 (CCC-2) is often applied to assess pragmatic language impairment which is highly prevalent in autism spectrum disorder (ASD) and several mental health conditions. We replicated previous findings on the limited applicability of the CCC-2 in clinical samples and the inconsistent findings concerning the factor structure. The aim of the present study was, thus, to develop a concise, simplified, and revised version of the CCC-2 in a large German-speaking sample. Four groups of children and adolescents aged 4 to 17 years were included: ASD (n = 195), intellectual disability (ID, n = 83), diverse mental health conditions (MHC, n = 144) and a typically developing control group (TD, n = 417). We reduced the original number of items from 70 to 39, based on item analysis, exploratory factor analysis and the exclusion of communication-unrelated items. The revised version, CCC-R (α = 0.96), consists of two empirically derived factors: a pragmatic-language (α = 0.96) and a grammatical-semantic-language factor (α = 0.93). All clinical groups (ASD, ID, and MHC) had significantly increased CCC-R total scores, with the highest scores being in the neurodevelopmental disorder groups (ASD and ID). In addition, we found group-specific patterns of elevated pragmatic-language scores in the ASD group and grammatical-semantic scores in the ID group. The CCC-R was comparable to the CCC-2 in distinguishing ASD from the other groups. The CCC-R is proposed as a simplified and easily applied, clinical questionnaire for caregivers, assessing pragmatic language impairments across neurodevelopmental disorders and mental health conditions. Lay Summary: The CCC-2 is a questionnaire designed to identify children who have problems in the social use of language, however, it is limited in its clinical application and exhibits inconsistent factors. We have created a shorter and simpler version of the CCC-2 that we have called the CCC-R which overcomes the previous limitations of the CCC-2. It consists of two subscales: pragmatic language and grammatical-semantic language. The CCC-R can be used as a short and clinically relevant caregiver questionnaire which assesses pragmatic language impairments in children and adolescents. Autism Res 2021, 14: 759–772. © 2021 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals LLC

Ray Optics at a Deep-Subwavelength Scale: A Transformation Optics Approach

We present a transformation optics approach for molding the light flow at the deep-subwavelength scale, using metamaterials with uniquely designed dispersion. By conformal transformation of the electromagnetic space, we develop a methodology for realizing subwavelength ray optics with curved ray trajectories. This enables deep-subwavelength-scale beams to flow through two- or three-dimensional spaces

Classical Analog of Electromagnetically Induced Absorption in Plasmonics

The ability to manipulate the phase shift between two resonantly coupled plasmonic oscillators in a controlled fashion has been unavailable up to now. Here we present a strategy to overcome this limitation by employing the benefits of near-field coupling on the one hand and retardation effects due to far-field coupling on the other hand. We theoretically and experimentally demonstrate that in the intermediate regime the coupling of a broad dipolar to a narrow dark quadrupolar plasmon resonance is possible while simultaneously allowing for a retardation-induced phase shift. This leads to constructive interference and enhanced absorption. The observed phenomenon can thus be termed a classical analog of electromagnetically induced absorption