A perspective on topological nanophotonics: Current status and future challenges

Abstract

Topological photonic systems, with their ability to host states protected against disorder and perturbation, allow us to do with photons what topological insulators do with electrons. Topological photonics can refer to electronic systems coupled with light or purely photonic setups. By shrinking these systems to the nanoscale, we can harness the enhanced sensitivity observed in nanoscale structures and combine this with the protection of the topological photonic states, allowing us to design photonic local density of states and to push towards one of the ultimate goals of modern science: the precise control of photons at the nanoscale. This is paramount for both nano-technological applications and also for fundamental research in light matter problems. For purely photonic systems, we work with bosonic rather than fermionic states, so the implementation of topology in these systems requires new paradigms. Trying to face these challenges has helped in the creation of the exciting new field of topological nanophotonics, with far-reaching applications. In this prospective article we review milestones in topological photonics and discuss how they can be built upon at the nanoscale. I. OVERVIEWOne of the ultimate goals of modern science is the precise control of photons at the nanoscale. Topological nanophotonics offers a promising path towards this aim.A key feature of topological condensed matter systems is the presence of topologically protected surface states immune to disorder and impurities. These unusual properties can be transferred to nanophotonic systems, allowing us to combine the high sensitivity of nanoscale systems with the robustness of topological states. We expect that this new field of topological nanophotonics will lead to a plethora of new applications and increased physical insight.In this perspective, as presented schematically in FIG. 1, we begin (section II) by exploring topology in electronic systems. We aim this section towards readers who are new to the topic, so begin at an introductory level where no prior knowledge of topology is assumed.In section III we introduce light, first by discussing how topological electronic systems can interact with light (section III A), then move onto the topic of topological photonic analogues (section III B), in which purely photonic platforms are used to mimic the physics of topological condensed matter systems.In section IV we discuss various paths via which topological photonics can be steered into the nanoscale. Excellent and extensive reviews already exist on topological photonics [1][2][3][4], and many platforms showcasing unique strengths and limitations are currently being studied in the drive towards new applications in topological photonics such as cold atoms [5], liquid helium [6], polaritons [7], acoustic [8] and mechanical systems [9] but in this work * marie.rider16@imperial.ac.uk † www.GianniniLab.com FIG. 1. Schematic overview Schematic showing the topics covered in this perspective.we restrict ourselves to nanostructures. We discuss the effo...

Bulk-edge correspondence and long-range hopping in the topological plasmonic chain

“…Topological insulators (TIs) are often described as materials which have insulating bulks but support surface or edge states that are strongly protected from disorder or other perturbations by topology. Some time after the introduction of topological physics in the Hermitian quantum world [1][2][3][4][5][6], photonic systems were shown to also exhibit topological properties [7][8][9][10][11][12][13][14][15][16][17]. These photonic topological insulators (PTIs) have exciting applications for unidirectional waveguides [10] and lasing [18][19][20] and show interesting effects in coupling to quantum emitters [21].…”

Manipulating topological valley modes in plasmonic metasurfaces

“…These states are reliant on the fractional spin of fermions. Therefore, whilst these electronic systems have inspired research into bosonic analogues, they require alternative strategies for creating topological states [21][22][23]. Unidirectional, i.e., non-reciprocal, edge states can be obtained for photons by breaking time-reversal symmetry through the use of strong magnetic fields [24,25].…”

Topological Phases of Polaritons in a Cavity Waveguide

“…Introduction.-The utility of topology in quantum materials has been proven by the revolutions in understanding of a range of phenomena, including the integer and anomalous quantum Hall effects, and the quantum spin-liquid states of antiferromagnets [1][2][3]. Recently, a rapidly growing research field known as topological nanophotonics has emerged [4,5], which seeks to harness the power of topological physics in a new generation of highly controllable light-based structures and devices [6][7][8]. It is envisaged that this topic will lead to a deeper understanding of light-matter interactions at a fundamental level [9,10], as well as novel applications including chiral lasers [11], robust integrated quantum optical circuits [12], and nonlinear light generators [13].…”