Quantum superposition demonstrated higher-order topological bound states in the continuum

Abstract

Higher-order topological insulators, as newly found non-trivial materials and structures, possess topological phases beyond the conventional bulk-boundary correspondence. In previous studies, in-gap boundary states such as the corner states were regarded as conclusive evidence for the emergence of higher-order topological insulators. Here, we present an experimental observation of a photonic higher-order topological insulator with corner states embedded into the bulk spectrum, denoted as the higher-order topological bound states in the continuum. Especially, we propose and experimentally demonstrate a new way to identify topological corner states by exciting them separately from the bulk states with photonic quantum superposition states. Our results extend the topological bound states in the continuum into higher-order cases, providing an unprecedented mechanism to achieve robust and localized states in a bulk spectrum. More importantly, our experiments exhibit the advantage of using the time evolution of quantum superposition states to identify topological corner modes, which may shed light on future exploration between quantum dynamics and higher-order topological photonics.

Progress in Topological Mechanics

“…In 2018, Schindler et al [13] proposed the notion of HOTIs. So far, the HO-TIs have been realized experimentally in photonics [91][92][93][94][95][96][97][98], acoustics [99][100][101][102][103][104], mechanical systems [105][106][107][108][109][110][111][112] and other classical waves systems [113][114][115] owing to their advantages in manufacturing, spectral analysis and local signal detection [15]. Next, we try to summarize the achievements in elastic systems from two categories of quantized multipole insulators and n C -symmetric HOTIs without quantized multipole moments.…”

Organic Higher-Order Topological Insulators: Heterotriangulene-Based Covalent Organic Frameworks

“…Higher-order TIs exhibit an exotic bulk-boundary correspondence principle since a second-order TI supports robust in-gap boundary states; this can lead to nontrivial fractional quasiparticles and provide a new architecture for quantum information processing and quantum computing. 33−36 The 2D higher-order TI phase has been experimentally realized in phononic, 37−39 photonic, 40,41 microwave circuit, 42 and electrical circuit 43,44 systems. In spite of their theoretical predictions in several 2D materials, 45−48 e.g., graphyne, 49 graphdiyne, 50,51 or twisted bilayer graphene, 52−54 higher-order TIs have been experimentally characterized to date in electronic systems limited to 3D materials, 55−57 calls for the further exploration of material candidates for 2D higher-order TIs.…”

“…, zero-dimensional corners in 2D materials or 1D hinges in 3D materials. Higher-order TIs exhibit an exotic bulk-boundary correspondence principle since a second-order TI supports robust in-gap boundary states; this can lead to nontrivial fractional quasiparticles and provide a new architecture for quantum information processing and quantum computing. − The 2D higher-order TI phase has been experimentally realized in phononic, − photonic, , microwave circuit, and electrical circuit , systems. In spite of their theoretical predictions in several 2D materials, − e.g.…”

Probing Phase Transition of Band Topology via Radiation Topology

“…For example, topological states merge with trivial bulk states when there is no full bandgap. [21][22][23][24] In this case, spectral measurements alone are not enough, the near-field distribution of the mode is needed to determine whether the state is topological. Thus, it is necessary and interesting to find new methods that investigates the band topology.…”