Abstract The synergy between topology and non-Hermiticity in photonics holds immense potential for next-generation optical devices that are robust against defects. However, most demonstrations of non-Hermitian and topological photonics have been limited to super-wavelength scales due to increased radiative losses at the deep-subwavelength scale. By carefully designing radiative losses at the nanoscale, we demonstrate a non-Hermitian plasmonic–dielectric metasurface in the visible with non-trivial topology. The metasurface is based on a fourth order passive parity-time symmetric system. The designed device exhibits an exceptional concentric ring in its momentum space and is described by a Hamiltonian with a non-Hermitian Z 3 ${\mathbb{Z}}_{3}$ topological invariant of V = −1. Fabricated devices are characterized using Fourier-space imaging for single-shot k -space measurements. Our results demonstrate a way to combine topology and non-Hermitian nanophotonics for designing robust devices with novel functionalities.
more »
« less
Non-Hermitian topological photonics
Recent years have witnessed a flurry of research activities in topological photonics, predominantly driven by the prospect for topological protection–a property that endows such systems with robustness against local defects, disorder, and perturbations. This field emerged in fermionic environments and primarily evolved within the framework of quantum mechanics which is by nature a Hermitian theory. However, in light of the ubiquitous presence of non-Hermiticity in a host of natural and artificial settings, one of the most pressing questions today is how non-Hermiticity may affect some of the predominant features of topological arrangements and whether or not novel topological phases may arise in non-conservative and out of equilibrium systems that are open to the environment. Here, we provide a brief overview of recent developments and ongoing efforts in this field and present our perspective on future directions and potential challenges. Special attention will be given to the interplay of topology and non-Hermiticity–an aspect that could open up new frontiers in physical sciences and could lead to promising opportunities in terms of applications in various disciplines of photonics.
more » « less- NSF-PAR ID:
- 10400503
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optical Materials Express
- Volume:
- 13
- Issue:
- 4
- ISSN:
- 2159-3930
- Page Range / eLocation ID:
- Article No. 870
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)Abstract In the past few years, concepts from non-Hermitian (NH) physics, originally developed within the context of quantum field theories, have been successfully deployed over a wide range of physical settings where wave dynamics are known to play a key role. In optics, a special class of NH Hamiltonians – which respects parity-time symmetry – has been intensely pursued along several fronts. What makes this family of systems so intriguing is the prospect of phase transitions and NH singularities that can in turn lead to a plethora of counterintuitive phenomena. Quite recently, these ideas have permeated several other fields of science and technology in a quest to achieve new behaviors and functionalities in nonconservative environments that would have otherwise been impossible in standard Hermitian arrangements. Here, we provide an overview of recent advancements in these emerging fields, with emphasis on photonic NH platforms, exceptional point dynamics, and the very promising interplay between non-Hermiticity and topological physics.more » « less
-
Non-Hermitian exceptional points (EPs) represent a special type of degeneracy where not only the eigenvalues coalesce, but also the eigenstates tend to collapse on each other. Recent studies have shown that in the presence of an EP, light-matter interactions are profoundly modified, leading to a host of novel optical phenomena ranging from enhanced sensitivity to chiral light transport. As of now, however, in order to stabilize a system at the vicinity of an exceptional point, its related parameters must be carefully tuned and/or continuously controlled. To overcome this limitation, here we introduce a new family of broadband exceptional points based on unidirectional coupling, implemented by incorporating an Sshaped waveguide in a microring cavity. In active settings, the resulting unidirectionality exhibits unprecedented resilience to perturbations, thus providing a robust and tunable approach for directly generating beams with distinct orbital angular momentum (OAM). This work could open up new possibilities for manipulating OAM degrees of freedom in applications pertaining to telecommunications and quantum computing, while at the same time may expand the notions of non-Hermiticity in the orbital angular momentum space.more » « less
-
more » « less
Abstract Synthetic dimensions, wherein dynamics occurs in a set of internal states, have found great success in recent years in exploring topological effects in cold atoms and photonics. However, the phenomena thus far explored have largely been restricted to the non-interacting or weakly interacting regimes. Here, we extend the synthetic dimensions playbook to strongly interacting systems of Rydberg atoms prepared in optical tweezer arrays. We use precise control over driving microwave fields to introduce a tunable
U (1) flux in a four-site lattice of coupled Rydberg levels. We find highly coherent dynamics, in good agreement with theory. Single atoms show oscillatory dynamics controllable by the gauge field. Small arrays of interacting atoms exhibit behavior suggestive of the emergence of ergodic and arrested dynamics in the regimes of intermediate and strong interactions, respectively. These demonstrations pave the way for future explorations of strongly interacting dynamics and many-body phases in Rydberg synthetic lattices. -
In this paper, we introduce a non-rigid registration pipeline for unorganized point clouds that may be topologically different. Standard warp field estimation algorithms, even under robust, discontinuity-preserving regularization, produce erratic motion estimates on boundaries associated with ‘close-to-open’ topology changes. We overcome this limitation by exploiting backward motion: in the opposite direction, a ‘close-to-open’ event becomes ‘open-to-close’, which is by default handled correctly. Our approach relies on a general, topology-agnostic warp field estimation algorithm, similar to those employed in recent dynamic reconstruction systems from RGB-D input. We improve motion estimation on boundaries associated with topology changes in an efficient post-processing phase. Based on both forward and (inverted) backward warp hypotheses, we explicitly detect regions of the deformed geometry that undergo topological changes by means of local deformation criteria and broadly classify them as ‘contacts’ or ‘separations’. Subsequently, the two motion hypotheses are seamlessly blended on a local basis, according to the type and proximity of detected events. Our method achieves state-of-the-art motion estimation accuracy on the MPI Sintel dataset. Experiments on a custom dataset with topological event annotations demonstrate the effectiveness of our pipeline in estimating motion on event boundaries, as well as promising performance in explicit topological event detection.more » « less
