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

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Yao Wang ◽  
Bi-Ye Xie ◽  
Yong-Heng Lu ◽  
Yi-Jun Chang ◽  
Hong-Fei Wang ◽  
...  
Keyword(s):  
Quantum Dynamics ◽  
Bound States ◽  
Topological Insulators ◽  
Higher Order ◽  
Conclusive Evidence ◽  
Localized States ◽  
Quantum Superposition ◽  
Boundary States ◽  
Superposition States ◽  
The Continuum

AbstractHigher-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.

scholarly journals Non-Abelian Bloch oscillations in higher-order topological insulators

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Di Liberto ◽  
N. Goldman ◽  
G. Palumbo
Keyword(s):  
Quantum Dynamics ◽  
Topological Insulators ◽  
Berry Phase ◽  
Center Of Mass ◽  
Higher Order ◽  
Topological Properties ◽  
Bloch Oscillations ◽  
Abelian Gauge ◽  
Synchronization Mechanism ◽  
Wide Range

AbstractBloch oscillations (BOs) are a fundamental phenomenon by which a wave packet undergoes a periodic motion in a lattice when subjected to a force. Observed in a wide range of synthetic systems, BOs are intrinsically related to geometric and topological properties of the underlying band structure. This has established BOs as a prominent tool for the detection of Berry-phase effects, including those described by non-Abelian gauge fields. In this work, we unveil a unique topological effect that manifests in the BOs of higher-order topological insulators through the interplay of non-Abelian Berry curvature and quantized Wilson loops. It is characterized by an oscillating Hall drift synchronized with a topologically-protected inter-band beating and a multiplied Bloch period. We elucidate that the origin of this synchronization mechanism relies on the periodic quantum dynamics of Wannier centers. Our work paves the way to the experimental detection of non-Abelian topological properties through the measurement of Berry phases and center-of-mass displacements.

scholarly journals Geometry symmetry-free and higher-order optical bound states in the continuum

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qingjia Zhou ◽  
Yangyang Fu ◽  
Lujun Huang ◽  
Qiannan Wu ◽  
Andrey Miroshnichenko ◽  
...  
Keyword(s):  
Significant Role ◽  
Bound States ◽  
Higher Order ◽  
Multiple Objects ◽  
Material Parameters ◽  
Geometrical Symmetry ◽  
Geometric Symmetry ◽  
Symmetry Protected ◽  
Zero Index ◽  
The Continuum

AbstractGeometrical symmetry plays a significant role in implementing robust, symmetry-protected, bound states in the continuum (BICs). However, this benefit is only theoretical in many cases since fabricated samples’ unavoidable imperfections may easily break the stringent geometrical requirements. Here we propose an approach by introducing the concept of geometrical-symmetry-free but symmetry-protected BICs, realized using the static-like environment induced by a zero-index metamaterial (ZIM). We find that robust BICs exist and are protected from the disordered distribution of multiple objects inside the ZIM host by its physical symmetries rather than geometrical ones. The geometric-symmetry-free BICs are robust, regardless of the objects’ external shapes and material parameters in the ZIM host. We further show theoretically and numerically that the existence of those higher-order BICs depends only on the number of objects. By practically designing a structural ZIM waveguide, the existence of BICs is numerically confirmed, as well as their independence on the presence of geometrical symmetry. Our findings provide a way of realizing higher-order BICs and link their properties to the disorder of photonic systems.

scholarly journals Geometry symmetry-free and Higher-order Optical Bound States in the Continuum

2021 ◽  
Author(s):  
Qingjia Zhou ◽  
Yangyang Fu ◽  
Lujun Huang ◽  
Qiannan Wu ◽  
Andrey Miroshnichenko ◽  
...  
Keyword(s):  
Significant Role ◽  
Bound States ◽  
Higher Order ◽  
Multiple Objects ◽  
New Approach ◽  
Geometrical Symmetry ◽  
Symmetry Protected ◽  
Zero Index ◽  
The Continuum

Abstract Geometrical symmetry plays a significant role in realizing robust, symmetry-protected, bound states in the continuum (BICs). However, this benefit is only theoretical in many cases since the unavoidable imperfections of fabricated samples may easily break the stringent geometrical requirements. Here we propose an essentially new approach by introducing the concept of geometrical-symmetry-free but symmetry-protected BICs, realized using the static-like environment induced by a zero-index metamaterial (ZIM). We find that robust BICs exist and are protected from the disordered distribution of multiple objects inside ZIM host by its physical symmetries rather than geometrical ones. We further show theoretically and numerically that the existence of those higher-order BICs depends only on the number of objects. By practically designing a structural ZIM waveguide, the existence of BICs is numerically confirmed, as well as their independence on the presence of geometrical symmetry. Our findings provide a new way of realizing higher-order BICs and link their properties to disorder of photonic systems.

Bound States in the Continuum of Higher-Order Topological Photonic Systems

2020 ◽  
Author(s):  
Alexander Cerjan ◽  
Marius Jürgensen ◽  
Wladimir A. Benalcazar ◽  
Sebabrata Mukherjee ◽  
Mikael C. Rechtsman
Keyword(s):  
Bound States ◽  
Higher Order ◽  
The Continuum

scholarly journals Nonlinear control of photonic higher-order topological bound states in the continuum

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Zhichan Hu ◽  
Domenico Bongiovanni ◽  
Dario Jukić ◽  
Ema Jajtić ◽  
Shiqi Xia ◽  
...  
Keyword(s):  
Bound States ◽  
Higher Order ◽  
Eigenvalue Spectrum ◽  
Proper Action ◽  
Continuum States ◽  
System A ◽  
Self Focusing ◽  
Topological Lattice ◽  
Symmetry Protected ◽  
The Continuum

AbstractHigher-order topological insulators (HOTIs) are recently discovered topological phases, possessing symmetry-protected corner states with fractional charges. An unexpected connection between these states and the seemingly unrelated phenomenon of bound states in the continuum (BICs) was recently unveiled. When nonlinearity is added to the HOTI system, a number of fundamentally important questions arise. For example, how does nonlinearity couple higher-order topological BICs with the rest of the system, including continuum states? In fact, thus far BICs in nonlinear HOTIs have remained unexplored. Here we unveil the interplay of nonlinearity, higher-order topology, and BICs in a photonic platform. We observe topological corner states that are also BICs in a laser-written second-order topological lattice and further demonstrate their nonlinear coupling with edge (but not bulk) modes under the proper action of both self-focusing and defocusing nonlinearities. Theoretically, we calculate the eigenvalue spectrum and analog of the Zak phase in the nonlinear regime, illustrating that a topological BIC can be actively tuned by nonlinearity in such a photonic HOTI. Our studies are applicable to other nonlinear HOTI systems, with promising applications in emerging topology-driven devices.

scholarly journals Discovery of higher-order topological insulators using the spin Hall conductivity as a topology signature

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Marcio Costa ◽  
Gabriel R. Schleder ◽  
Carlos Mera Acosta ◽  
Antonio C. M. Padilha ◽  
Frank Cerasoli ◽  
...  
Keyword(s):  
Density Functional ◽  
Topological Insulators ◽  
Tight Binding ◽  
Density Functional Theory Calculations ◽  
Higher Order ◽  
Hall Conductivity ◽  
Two Dimensional ◽  
Boundary States ◽  
Potential Applications ◽  
Spin Hall Conductivity

AbstractThe discovery and realization of topological insulators, a phase of matter which hosts metallic boundary states when the d-dimension insulating bulk is confined to (d − 1)-dimensions, led to several potential applications. Recently, it was shown that protected topological states can manifest in (d − 2)-dimensions, such as hinge and corner states for three- and two-dimensional systems, respectively. These nontrivial materials are named higher-order topological insulators (HOTIs). Here we show a connection between spin Hall effect and HOTIs using a combination of ab initio calculations and tight-binding modeling. The model demonstrates how a non-zero bulk midgap spin Hall conductivity (SHC) emerges within the HOTI phase. Following this, we performed high-throughput density functional theory calculations to find unknown HOTIs, using the SHC as a criterion. We calculated the SHC of 693 insulators resulting in seven stable two-dimensional HOTIs. Our work guides novel experimental and theoretical advances towards higher-order topological insulator realization and applications.

scholarly journals Displacement-mediated bound states in the continuum in all-dielectric superlattice metasurfaces

PhotoniX ◽  
2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Tan Shi ◽  
Zi-Lan Deng ◽  
Qing-An Tu ◽  
Yaoyu Cao ◽  
Xiangping Li
Keyword(s):  
Bound States ◽  
Relative Displacement ◽  
Localized States ◽  
Practical Applications ◽  
High Q ◽  
Magnetic Mode ◽  
Toroidal Mode ◽  
Resonance Coupling ◽  
Field Symmetry ◽  
The Continuum

AbstractBound states in the continuum (BICs) are localized states coexisting with extended waves inside the continuous spectrum range, which have infinite lifetimes without any radiation. To extract high-Q quasi-BIC resonances from the symmetry-protected BIC for practical applications, symmetry-breaking approaches are usually exploited, either by slightly breaking the excitation field symmetry or structure symmetry. Here, we introduce an all-dielectric superlattice metasurface that can symmetry-compatibly convert BIC states into high-Q quasi-BIC modes based on the guided-mode resonance coupling by relative displacement tuning. The metasurface is composed of a superlattice of multiple nanobeams, supporting both magnetic mode and toroidal mode with large tunability. Both modes can interact with the incident continuum by mediating the displacement between nanobeams, which empowers dual asymmetric Fano resonances with high Q-factors. The bandwidth of the toroidal mode under y-polarized incidences and that of the magnetic mode under x-polarized incidences can be readily tuned by the local displacement between nanobeams in each unit cell. Such displacement-mediated BIC resonance is promising for various applications such as bio-molecule sensing and low threshold lasing.

scholarly journals Displacement-mediated bound states in the continuum in all-dielectric superlattice metasurfaces

2021 ◽  
Author(s):  
Tan Shi ◽  
Zilan Deng ◽  
Qing-An Tu ◽  
Yaoyu Cao ◽  
Xiangping Li
Keyword(s):  
Bound States ◽  
Relative Displacement ◽  
Localized States ◽  
Practical Applications ◽  
High Q ◽  
Magnetic Mode ◽  
Toroidal Mode ◽  
Resonance Coupling ◽  
Field Symmetry ◽  
The Continuum

Abstract Bound states in the continuum (BICs) are localized states coexisting with extended waves inside the continuous spectrum range, which have infinite lifetimes without any radiation. To extract high-Q quasi-BIC resonances from the symmetry-protected BIC for practical applications, symmetry-breaking approaches are usually exploited, either by slightly breaking the excitation field symmetry or structure symmetry. Here, we introduce an all-dielectric superlattice metasurface that can symmetry-compatibly convert BIC states into high-Q quasi-BIC modes based on the guided-mode resonance coupling by relative displacement tuning. The metasurface is composed of a superlattice of multiple nanobeams, supporting both magnetic mode and toroidal mode with large tunability. Both modes can interact with the incident continuum by mediating the displacement between nanobeams, which empowers dual asymmetric Fano resonances with high Q-factors. The bandwidth of the toroidal mode under TE-polarized incidences and that of the magnetic mode under TM-polarized incidences can be readily tuned by the local displacement between nanobeams in each unit cell. Such displacement-mediated BIC resonance is promising for various applications such as bio-molecule sensing and low threshold lasing.

Sign in / Sign up

Export Citation Format

Share Document