scholarly journals Nonlinear tuning of PT symmetry and non-Hermitian topological states

Science ◽  
2021 ◽  
Vol 372 (6537) ◽  
pp. 72-76
Author(s):  
Shiqi Xia ◽  
Dimitrios Kaltsas ◽  
Daohong Song ◽  
Ioannis Komis ◽  
Jingjun Xu ◽  
...  
Keyword(s):  
Single Channel ◽  
Topological Defect ◽  
Pt Symmetry ◽  
Zero Modes ◽  
Light Manipulation ◽  
And Topology ◽  
Topological States ◽  
Device Applications ◽  
Local Nonlinearity ◽  
Channel Control

Topology, parity-time (PT) symmetry, and nonlinearity are at the origin of many fundamental phenomena in complex systems across the natural sciences, but their mutual interplay remains unexplored. We established a nonlinear non-Hermitian topological platform for active tuning of PT symmetry and topological states. We found that the loss in a topological defect potential in a non-Hermitian photonic lattice can be tuned solely by nonlinearity, enabling the transition between PT-symmetric and non–PT-symmetric regimes and the maneuvering of topological zero modes. The interaction between two apparently antagonistic effects is revealed: the sensitivity close to exceptional points and the robustness of non-Hermitian topological states. Our scheme using single-channel control of global PT symmetry and topology via local nonlinearity may provide opportunities for unconventional light manipulation and device applications.

Implementation of a single-channel active noise control system with multiple reference sensors

2020 ◽  
Vol 68 (5) ◽  
pp. 358-366
Author(s):  
H.E. Oh ◽  
W.B. Jeong ◽  
C. Hong
Keyword(s):  
Single Channel ◽  
Control Method ◽  
Reference Signal ◽  
Active Noise Control ◽  
Multiple Source ◽  
Weighted Sum ◽  
Reference Signals ◽  
Feedforward Controller ◽  
Channel Control ◽  
Source Signals

When multiple sources contribute competitively to the noise level, multi-channel control architecture is needed, leading to more cost and time for control computation. We, hence, are concerned with a single-channel control method with a single-reference signal obtained from a linear combination of the multiple source signals. First, we selected 3 source signal sensors for the reference signals and the error sensor, selected a proper actuator and designed the controllers: 3 cases of single-channel feedforward controllers with a single-reference signal respectively from the source signals, a multi-channel feedforward controller with the reference signals from the source signals, and the proposed controller with the reference signal from weighted sum of the source signals. The weighting factors and the filter coefficients of the controller were determined by the FxLMS algorithm. An experiment was then performed to confirm the effectiveness of the proposed method comparing the control performance with other methods for a tower air conditioner. The overall sound pressure level (SPL) detected by the error sensor is compared to evaluate their performance. The reduction in the overall SPL was obtained by 4.74 dB, 1.96 dB and 6.62 dB, respectively, when using each of the 3 reference signals. Also, the overall SPL was reduced by 7.12 dB when using the multi-reference controller and by 7.66 dB when using the proposed controller. Conclusively, under the multiple source contribution, a single-channel feed forward controller with the reference signal from a weighted sum of the source signals works well with lower cost than multi-channel feedforward controller.

scholarly journals Topologically protected optical signal processing using parity–time-symmetric oscillation quenching

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sunkyu Yu ◽  
Xianji Piao ◽  
Namkyoo Park
Keyword(s):  
Signal Processing ◽  
Degrees Of Freedom ◽  
Quantum Hall ◽  
Optical Signal ◽  
Pt Symmetry ◽  
Coupled Systems ◽  
Fermi Surfaces ◽  
Topological States ◽  
Topological Geometry ◽  
Quenching Mechanisms

Abstract The concept of topology is universally observed in various physical objects when the objects can be described by geometric structures. Although a representative example is the knotted geometry of wavefunctions in reciprocal space for quantum Hall family and topological insulators, topological states have also been defined for other physical quantities, such as topologically distinct Fermi surfaces and enhanced lattice degrees of freedom in hyperbolic geometry. Here, we investigate a different class of topological states – topological geometry of dynamical state trajectories – in non-Hermitian and nonlinear optical dynamics, revealing topologically protected oscillation quenching mechanisms determined by parity–time (PT) symmetry. For coupled systems composed of nonlinear gain and loss elements, we classify the topology of equilibria separately for unbroken and broken PT symmetry, which result in distinct oscillation quenching mechanisms: amplitude death and oscillation death. We then show that these PT-symmetric quenching mechanisms lead to immunity against temporal perturbations, enabling the applications of topologically protected laser modulation and rectification. The observed connection between the topological geometry of dynamical states, oscillation quenching phenomena in dynamical systems theory, and PT symmetry provides a powerful toolkit for noise-immune signal processing.

Nonlinear Control of PT-symmetry and Topological States

2021 ◽  
Author(s):  
Shiqi Xia ◽  
Dimitrios Kaltsas ◽  
Daohong Song ◽  
Ioannis Komis ◽  
Jingjun Xu ◽  
...  
Keyword(s):  
Nonlinear Control ◽  
Pt Symmetry ◽  
Topological States

scholarly journals The effect of moiré superstructures on topological edge states in twisted bismuthene homojunctions

2020 ◽  
Vol 6 (23) ◽  
pp. eaba2773 ◽  
Author(s):  
Jian Gou ◽  
Longjuan Kong ◽  
Xiaoyue He ◽  
Yu Li Huang ◽  
Jiatao Sun ◽  
...  
Keyword(s):  
Single Layer ◽  
Scanning Tunneling ◽  
Edge States ◽  
First Principles Calculations ◽  
Tunneling Microscopy ◽  
Force Microscopy ◽  
Atomic Force ◽  
Spatially Distributed ◽  
Topological States ◽  
Device Applications

Creating and controlling the topological properties of two-dimensional topological insulators is essential for spintronic device applications. Here, we report the successful growth of bismuth homostructure consisting of monolayer bismuthene and single-layer black phosphorus–like Bi (BP-Bi) on the HOPG surface. Combining scanning tunneling microscopy/spectroscopy with noncontact atomic force microscopy, moiré superstructures with twist angles in the bismuth homostructure and the modulation of topological edge states of bismuthene were observed and studied. First-principles calculations reproduced the moiré superlattice and indicated that the structure fluctuation is ascribed to the stacking modes between bismuthene and BP-Bi, which induce spatially distributed interface interactions in the bismuth homostructure. The modulation of topological edge states is directly related to the variation of interlayer interactions. Our results suggest a promising pathway to tailor the topological states through interfacial interactions.

scholarly journals Symmetry-protected hierarchy of anomalous multipole topological band gaps in nonsymmorphic metacrystals

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Xiujuan Zhang ◽  
Zhi-Kang Lin ◽  
Hai-Xiao Wang ◽  
Zhan Xiong ◽  
Yuan Tian ◽  
...  
Keyword(s):  
Band Gap ◽  
Topological States Of Matter ◽  
Quantum Spin ◽  
Band Gaps ◽  
Quantum Spin Hall Effect ◽  
Classical Systems ◽  
Topological Materials ◽  
And Topology ◽  
Topological States ◽  
Symmetry Protected

AbstractSymmetry and topology are two fundamental aspects of many quantum states of matter. Recently new topological materials, higher-order topological insulators, were discovered, featuring bulk–edge–corner correspondence that goes beyond the conventional topological paradigms. Here we discover experimentally that the nonsymmorphic p4g acoustic metacrystals host a symmetry-protected hierarchy of topological multipoles: the lowest band gap has a quantized Wannier dipole and can mimic the quantum spin Hall effect, whereas the second band gap exhibits quadrupole topology with anomalous Wannier bands. Such a topological hierarchy allows us to observe experimentally distinct, multiplexed topological phenomena and to reveal a topological transition triggered by the geometry transition from the p4g group to the C4v group, which demonstrates elegantly the fundamental interplay between symmetry and topology. Our study demonstrates that classical systems with controllable geometry can serve as powerful simulators for the discovery of novel topological states of matter and their phase transitions.

Single-channel control of a two-channel system

1979 ◽  
Vol 24 (3) ◽  
pp. 491-492 ◽  
Author(s):  
J. Potter ◽  
B. Anderson ◽  
A. Morse
Keyword(s):  
Single Channel ◽  
Channel System ◽  
Channel Control

PT-symmetry breaking of topological defect-states in SSH micro-ring laser arrays

2017 ◽  
Author(s):  
S. Wittek ◽  
M. Parto ◽  
H. Hodaei ◽  
G. Harari ◽  
M. Bandres ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Ring Laser ◽  
Topological Defect ◽  
Pt Symmetry ◽  
Defect States ◽  
Laser Arrays

scholarly journals Decoherence and relaxation of topological states in extended quantum Ising models

2019 ◽  
Vol 6 (3) ◽  
Author(s):  
Hannes Weisbrich ◽  
Wolfgang Belzig ◽  
Gianluca Rastelli
Keyword(s):  
Ising Models ◽  
Transverse Magnetic ◽  
Topological Phase ◽  
Relaxation Dynamics ◽  
Many Body ◽  
Lindblad Equation ◽  
And Topology ◽  
Local Fluctuations ◽  
Topological States ◽  
The Many

We study the decoherence and the relaxation dynamics of topological states in an extended class of quantum Ising chains which can present a multidimensional ground state subspace. The leading interaction of the spins with the environment is assumed to be the local fluctuations of the transverse magnetic field. By deriving the Lindblad equation using the many-body states, we investigate the relation between decoherence, energy relaxation and topology. In particular, in the topological phase and at low temperature, we analyze the dephasing rates between the different degenerate ground states.

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