Roadmap on structured light

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.Peer ReviewedPostprint (published version

Magnetism in curved geometries

Curvature impacts physical properties across multiple length scales, ranging from the macroscopic scale, where the shape and size vary drastically with the curvature, to the nanoscale at interfaces and inhomogeneities in materials with structural, chemical, electronic, and magnetic short-range order. In quantum materials, where correlations, entanglement, and topology dominate, the curvature opens the path to novel characteristics and phenomena that have recently emerged and could have a dramatic impact on future fundamental and applied studies of materials. Particularly, magnetic systems hosting non-collinear and topological states and 3D magnetic nanostructures strongly benefit from treating curvature as a new design parameter to explore prospective applications in the magnetic field and stress sensing, microrobotics, and information processing and storage. This Perspective gives an overview of recent progress in synthesis, theory, and characterization studies and discusses future directions, challenges, and application potential of the harnessing curvature for 3D nanomagnetism

Nnanoscale light-matter interactions: fundamentals and applications

Novel phenomena and promising applications have been emerging from nanoscience and nanotechnology research over recent decades. Particularly, people pursue a better understanding of how light and matter interact with each other at the nanoscale. This dissertation will present our work on the relevant topics, including ultrafast optical generation and manipulation of nanoscale phonons, metamaterials for thermal management, and cooperative chirality in inorganic nano-systems. Through an acoustically mismatched nanoscale interface, interfacial phonon coupling may lead to a coherently modulated phonon spectrum, which however has been less studied. We have demonstrated unambiguous experimental evidences of coherent interfacial phonon coupling between the core and shell constituents by employing a well-designed nanoscale core-shell structure with a precisely tunable interface as a model system. Furthermore, the observed phonon modes can be selectively tailored in a highly controllable manner by different ultrafast pulse control schemes. This study represents an important step towards nanoscale phonon engineering with rationally tailored nanostructures as building blocks. Metamaterials, which are artificially patterned micro/nano-structures, are studied for thermal management. For this purpose, we propose patterned arrays in different forms, including micropillar arrays and fiber arrays. We have discovered the structural dependence of the arrays’ characteristic resonance and emission properties, and how the properties are impacted in imperfect patterns which are common in real life. This study provides new perspectives on metamaterials for thermal management and the textile industry. Lastly, chiral light-matter interaction is studied in a novel type of inorganic nanocrystals, consisting of both crystallographic and geometric chirality. We build up a general model for simulating electromagnetic response of chiral objects and extract the materials parameters from experimental data of the achiral-shape nanocrystals. By simulating nanocrystal of different geometries and comparing with experimental circular dichroism spectra, the unique spectral features from the nanocrystals’ intrinsic crystallographic chirality, geometric chirality and their interplay are identified. Besides, an excellent agreement is achieved between the simulation and the experiment. This result opens up the opportunities for new chiroptical devices and chiral discrimination technology

Vector field patterning of light: methods and applications

Light (electromagnetic field in general) is a main form of energy in nature. Thanks to centuries of scientific investigations, we nowadays possess a fairly complete knowledge of its properties and behavior. In particular, conserved quantities, such as energy and momentum of light, have been the subject of experimental and theoretical activities leading to a great advancement of science and technology. The momentum of light can be distinguished in two different kinds, that is, linear momentum and angular momentum. The main focus of this work is on the angular momentum of light and its manipulation in order to control the vectorial pattern of the light field. The angular momentum of the electromagnetic field expresses two different forms of rotation called spin angular momentum and orbital angular momentum. We focus on the cases in which these two rotations can be considered independent. The first is related to the state of the polarization, and the second to the spatial distribution of the beam. Since they are independent, each of these two rotations can be studied separately and used in different applications. The interaction between them, however, attracts great attention, since a beam may possess both at the same time. The device called q-plate is one possible technique which results in spin-orbit coupling. In this work, we present the importance of the interaction of spin and orbital angular momentum for certain applications. For this purpose, we have designed devices (e.g., q-plates) that combine both forms of angular momentum. This thesis consists of four chapters as follows: • Chapter 1: In this chapter, we give an introduction about light angular momentum, in particular orbital angular momentum. Various methods for generating helical modes, in particular q-plates, are discussed. • Chapter 2: In this chapter, we discuss the optical fibers and the coupling efficiency in the fundamental mode of a single-mode step-index fiber. The main focus of this chapter is on amplitude matching to increase the coupling efficiency. • Chapter 3: Reaching the highest possible coupling efficiency cannot be achieved by amplitude matching alone. Another important factor is polarization matching, which is the interest of this chapter. We present a novel application for q plates to improve the coupling efficiency by manipulating the polarization structure of the input beam. • Chapter 4: In this last chapter, we investigate the possibility of beam tailoring and polarization singularity generation using Spatially Varying Axes retardation wave Plates (SVAPs), devices which generalize the q-plates. Finally, we conclude this work by presenting the results and possible prospects for future work

Synthetic dimensions for topological and quantum phases: Perspective

In this Perspective article we report on recent progress on studies of synthetic dimensions, mostly, but not only, based on the research realized around the Barcelona groups (ICFO, UAB), Donostia (DIPC), Pozna\'n (UAM), Krak\'ow (UJ), and Allahabad (HRI). The concept of synthetic dimensions works particularly well in atomic physics, quantum optics, and photonics, where the internal degrees of freedom (Zeeman sublevels of the ground state, metastable excited states, or motional states for atoms, and angular momentum states or transverse modes for photons) provide the synthetic space. We describe our attempts to design quantum simulators with synthetic dimensions, to mimic curved spaces, artificial gauge fields, lattice gauge theories, twistronics, quantum random walks, and more

Discovery of enhanced lattice dynamics in a single-layered hybrid perovskite

Layered hybrid perovskites have attracted much attention in recent years due to their emergent physical properties and exceptional functional performances, but the coexistence of lattice order and structural disorder severely hinders our understanding of these materials. One unsolved problem regards how the lattice dynamics are affected by the dimensional engineering of the inorganic frameworks and the interaction with the molecular moieties. Here, we address this question by using a combination of high-resolution spontaneous Raman scattering, high-field terahertz spectroscopy, and molecular dynamics simulations. This approach enables us to reveal the structural vibrations and disorder in and out of equilibrium and provides surprising observables that differentiate single- and double-layered perovskites. While no distinct vibrational coherence is observed in double-layer perovskites, we discover that an off-resonant terahertz pulse can selectively drive a long-lived coherent phonon mode through a two-photon process in the single-layered system. This difference highlights the dramatic change in the lattice environment as the dimension is reduced. The present findings pave the way for the ultrafast structural engineering of hybrid lattices as well as for developing high-speed optical modulators based on layered perovskites

Towards chiral polaritons

Coupling between light and material excitations underlies a wide range of optical phenomena. Polaritons are eigenstates of a coupled system with hybridized wave function. Owing to their hybrid composition, polaritons exhibit at the same time properties typical for photonic and electronic excitations, thus offering new ways for controlling electronic transport and even chemical kinetics. While most theoretical and experimental efforts have been focused on polaritons with electric-dipole coupling between light and matter, in chiral quantum emitters, electronic transitions are characterized by simultaneously nonzero electric and magnetic dipole moments. Geometrical chirality affects the optical properties of materials in a profound way and enables phenomena that underlie our ability to discriminate enantiomers of chiral molecules. Thus, it is natural to wonder what kinds of novel effects chirality may enable in the realm of strong light-matter coupling. Right now, this field located at the intersection of nanophotonics, quantum optics, and chemistry is in its infancy. In this Perspective, we offer our view towards chiral polaritons. We review basic physical concepts underlying chirality of matter and electromagnetic field, discuss the main theoretical and experimental challenges that need to be solved, and consider novel effects that could be enabled by strong coupling between chiral light and matter