Tunable negative refraction without absorption via electromagnetically induced chirality

We show that negative refraction with minimal absorption can be obtained by means of quantum interference effects similar to electromagnetically induced transparency. Coupling a magnetic dipole transition coherently with an electric dipole transition leads to electromagnetically induced chirality, which can provide negative refraction without requiring negative permeability, and also suppresses absorption. This technique allows negative refraction in the optical regime at densities where the magnetic susceptibility is still small and with refraction/absorption ratios that are orders of magnitude larger than those achievable previously. Furthermore, the value of the refractive index can be fine-tuned via external laser fields, which is essential for practical realization of sub-diffraction-limit imaging.Comment: 4 pages, 5 figures (shortened version, submitted to PRL

Comparison of Quantum and Classical Local-field Effects on Two-Level Atoms in a Dielectric

The macroscopic quantum theory of the electromagnetic field in a dielectric medium interacting with a dense collection of embedded two-level atoms fails to reproduce a result that is obtained from an application of the classical Lorentz local-field condition. Specifically, macroscopic quantum electrodynamics predicts that the Lorentz redshift of the resonance frequency of the atoms will be enhanced by a factor of the refractive index n of the host medium. However, an enhancement factor of (n*n+2)/3 is derived using the Bloembergen procedure in which the classical Lorentz local-field condition is applied to the optical Bloch equations. Both derivations are short and uncomplicated and are based on well-established physical theories, yet lead to contradictory results. Microscopic quantum electrodynamics confirms the classical local-field-based results. Then the application of macroscopic quantum electrodynamic theory to embedded atoms is proved false by a specific example in which both the correspondence principle and microscopic theory of quantum electrodynamics are violated.Comment: Published version with rewritten abstract and introductio

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