Hanan Herzig Sheinfux

Quantum Čerenkov Radiation: Spectral Cutoffs and the Role of Spin and Orbital Angular Momentum

We show that the well-known Cerenkov effect contains new phenomena arising from the quantum nature of charged particles. The Cerenkov transition amplitudes allow coupling between the charged particle and the emitted photon through their orbital angular momentum and spin, by scattering into preferred angles and polarizations. Importantly, the spectral response reveals a discontinuity immediately below a frequency cutoff that can occur in the optical region. Near this cutoff, the intensity of the conventional Cerenkov radiation (CR) is very small but still finite, while our quantum calculation predicts exactly zero intensity above the cutoff. Below that cutoff, with proper shaping of electron beams (ebeams), we predict that the traditional CR angle splits into two distinctive cones of photonic shockwaves. One of the shockwaves can move along a backward cone, otherwise considered impossible for conventional CR in ordinary matter. Our findings are observable for ebeams with realistic parameters, offering new applications including novel quantum optics sources, and opening a new realm for Cerenkov detectors involving the spin and orbital angular momentum of charged particles.

Observation of Anderson localization in disordered nanophotonic structures

Localizing light at the nanometer scale Waves will propagate through a medium until scattering processes result in the excitation gradually dying away. Introducing disorder can affect that propagation by increasing the scattering, potentially reaching a point where transport is stopped. Typically, the length scale of the disorder is larger than the propagating waves. Herzig Sheinfux et al. now show that a stack of several-nanometer-thick layers of alternating high- and low-refractive- index material can result in the localization of light. Such deep-subwavelength structures could provide a route to manipulating light on the nanometer scale. Science, this issue p. 953 Anderson localization of light is observed for deep subwavelength structures. Anderson localization is an interference effect crucial to the understanding of waves in disordered media. However, localization is expected to become negligible when the features of the disordered structure are much smaller than the wavelength. Here we experimentally demonstrate the localization of light in a disordered dielectric multilayer with an average layer thickness of 15 nanometers, deep into the subwavelength regime. We observe strong disorder-induced reflections that show that the interplay of localization and evanescence can lead to a substantial decrease in transmission, or the opposite feature of enhanced transmission. This deep-subwavelength Anderson localization exhibits extreme sensitivity: Varying the thickness of a single layer by 2 nanometers changes the reflection appreciably. This sensitivity, approaching the atomic scale, holds the promise of extreme subwavelength sensing.

Interplay between evanescence and disorder in deep subwavelength photonic structures

Deep subwavelength features are expected to have minimal impact on wave transport. Here we show that in contrast to this common understanding, disorder can have a dramatic effect in a one-dimensional disordered optical system with spatial features a thousand times smaller than the wavelength. We examine a unique regime of Anderson localization where the localization length is shown to scale linearly with the wavelength instead of diverging, because of the role of evanescent waves. In addition, we demonstrate an unusual order of magnitude enhancement of transmission induced due to localization. These results are described for electromagnetic waves, but are directly relevant to other wave systems such as electrons in multi-quantum-well structures.

Author Correction: Interplay between evanescence and disorder in deep subwavelength photonic structures

This corrects the article DOI: 10.1038/ncomms12927.

Dynamic localization by curved space

We present the first study on the interplay between lattice wave dynamics and curved space. We demonstrate Bloch oscillations and dynamic localization induced by space curvature, for configurations which in flat-space show only discrete diffraction.

Experimental demonstration of waveguiding by artificial gauge field

We experimentally demonstrate, for the first time, waveguiding using artificial gauge fields. We use a system of waveguide arrays where the gauge field, arising by tilting the waveguides, affects transversal dynamics and generates guided modes.

Total internal reflection in gain media

We resolve the controversy around total internal reflection from gain media, propose new effects of (extremely) amplified reflection from a single interface, and snow sensitivity to subwavelength features.

Enhanced evanescent transport and Goos-Hanchen localization in a disordered dielectric multilayer

We show that disorder in dielectric structures made of multiple layers of deep subwavelength thickness can induce extremely short-ranged localization. Additionally, the disorder can convert evanescent waves into bulk localized modes, enhancing transport dramatically (*10,000).

Shaping Light in Complex Settings

My thesis presents new classes of accelerating beams in nonlinear optics and electromagnetism. These ideas apply to any wave system, recently leading to accelerating wavepackets of Diracs fermions, revealing intriguing phenomena in relativistic quantum mechanics.