Revealing Fano Combs in Directional Mie Scattering

The constructive interference of light reflecting on the inner surface of a dielectric sphere results in a rich Mie scattering spectrum. Each resonance can be understood through a quantum-mechanical analogy, while the structure of the full spectrum is predicted to be a series of Fano resonances. However, the overlap of all the different modes results in such a complex spectrum that an intuitive understanding of the full, underlying structure is still missing. Here we present a directional Mie spectrum obtained by selecting a particular polarization and direction of the scattering of levitating water droplets. We find a significantly simplified spectrum organized in distinct, consecutive Mie Fano Combs composed of equidistant resonances that smoothly evolve from wide Lorentzians into sharp Fano profiles. We then fully explain all these characteristics by expanding on the quantum-mechanical analogy. This makes it possible to understand Mie spectra intuitively without the need for computational simulations.

Improved Superconducting Qubit State Readout by Path Interference

High fidelity single shot qubit state readout is essential for many quantum information processing protocols. In superconducting quantum circuit, the qubit state is usually determined by detecting the dispersive frequency shift of a microwave cavity from either transmission or reflection. We demonstrate the use of constructive interference between the transmitted and reflected signal to optimize the qubit state readout, with which we find a better resolved state discrimination and an improved qubit readout fidelity. As a simple and convenient approach, our scheme can be combined with other qubit readout methods based on the discrimination of cavity photon states to further improve the qubit state readout.

Interference Utilization Precoding in Multi-Cluster IoT Networks

In Internet-of-Things, downlink multi-device interference has long been considered as a harmful element deteriorating system performance, and thus the principle of the classic interference-mitigation based precoding is to suppress the multi-device interference by exploiting the spatial orthogonality. In recent years, a judicious interference utilization precoding has been developed, which is capable of exploiting multi-device interference as a beneficial element for improving device’s reception performance, thus reducing downlink communication latency. In this review paper, we aim to review the emerging interference utilization precoding techniques. We first briefly introduce the concept of constructive interference, and then we present two generic downlink interference-utilization optimizations, which utilizes the multi-device interference for enhancing system performance. Afterwards, the application of interference utilization precoding is discussed in multi-cluster scenario. Finally, some open challenges and future research topics are envisaged.

Design of Metasurface with Nanoslits on Elliptical Curves for Generation of Dual-Channel Vector Beams

The manipulations of nanoscale multi-channel vector beams (VBs) by metasurfaces hold potential applications in various important fields. In this paper, the metasurface with two sets of nanoslits arranged on elliptic curves was proposed to generate the dual-channel focused vector beams (FVBs). Each set of nanoslits was composed of the in-phase and the out-of-phase groups of nanoslits to introduce the constructive interference and destructive interference of the output light field of the nanoslits, focusing the converted spin component and eliminating the incident spin component at the focal point. The two sets of nanoslits for the channels at the two focal points were interleaved on the same ellipses, and by setting their parameters independently, the FVBs in the two channels are generated under illumination of linearly polarized light, while their orders and polarization states of FVBs were controlled independently. The generation of the FVBs with the designed metasurfaces was demonstrated by the finite-difference time domain (FDTD) simulations and by the experimental verifications. The work in this paper is of great significance for the generation of miniaturized multi-channel VBs and for broadening the applications of metasurfaces.

Temporal analog of Fabry-Pérot resonator via coherent population trapping

Ramsey spectroscopy via coherent population trapping (CPT) is essential in precision measurements. The conventional CPT-Ramsey fringes contain numbers of almost identical oscillations and so that it is difficult to identify the central fringe. Here we experimentally demonstrate a temporal analog of Fabry–Pérot resonator via double-Λ CPT of laser-cooled 87Rb atoms. By inserting a periodic CPT pulse train between the two CPT-Ramsey pulses, due to the constructive interference of spin coherence, the transmission spectrum appears as a comb of equidistant peaks in frequency domain and thus the central Ramsey fringe can be easily identified. From the five-level Bloch equations for our double-Λ system, we find that the multi-pulse CPT interference can be regarded as a temporal analog of Fabry–Pérot resonator. Because of the small amplitude difference between the two Landé g factors, each peak splits into two when the external magnetic field is not too weak. This splitting is exactly linear with the magnetic field strength and thus can be used for measuring a magnetic field without involving magneto-sensitive transitions.

Signal Enhancement in Surface Crack Detection with Gas-Coupled Laser Acoustic Detection

Ultrasonic signal enhancement resulting from constructive interference between direct Rayleigh waves and same waves reflected by a surface defect is exploited to increase crack identification capabilities of the Gas-Coupled Laser Acoustic Detection (GCLAD) non-contact detection technology. Highlights from simulations are provided regarding the interference phenomenon in the solid and its propagation in air, where GCLAD detection occurs. Experimental campaigns are preliminarily performed on a bar to evidence the effect of cracks on the GCLAD acquired signals. Then, a signal enhancement of +30% is reached on a plate, implying that defects are efficiently scanned by moving the GCLAD in proximity of the discontinuity. Since the GCLAD allows monitoring points of a piece belonging to the same line at once, its translation in one direction is sufficient to perform a two-dimensional scan, entailing reduction of inspection time and simple automation of the interrogation layout compared to other traditional or signal enhancement-based techniques.

The data reduction for different Speckle images using MATLAB and IMAGE pro-plus

When coherent light rays can be incident on an optically rough object it will scatter randomly through all directions. Interference of these scattered rays leads to the formation of a bright spots (constructive interference), and dark spots (destructive interference), these are called Laser Speckles.

Evaluating the applicability of a screen diffraction approximation to local volcano infrasound

Atmospheric acoustic waves from volcanoes at infrasonic frequencies (0.01–20 Hz) can be used to estimate source parameters for hazard modeling, but signals are often distorted by wavefield interactions with topography, even at local recording distances (<15 km). We present new developments toward a simple empirical approach to estimate attenuation by topographic diffraction at reduced computational cost. We investigate the applicability of a thin screen diffraction relationship developed by Maekawa [1968, doi: https://doi.org/10.1016/0003-682X(68)90020- 0]. We use a 2D axisymmetric finite-difference method to show that this relationship accurately predicts power losses for infrasound diffraction over an idealized kilometer-scale screen; thus validating the scaling to infrasonic wavelengths. However, the Maekawa relationship overestimates attenuation for realistic volcano topography (using Sakurajima Volcano as an example). The attenuating effect of diffraction may be counteracted by constructive interference of multiple reflections along concave volcano slopes. We conclude that the Maekawa relationship is insufficient as formulated for volcano infrasound, and suggest modifications that may improve the prediction capability.