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Efficient and stable wireless power transfer based on the non-hermitian physics

Chinese physics B 2022年第1期31卷 37-44页

作者：曾超郭志伟祝可嘉范才富李果江俊李云辉江海涛羊亚平孙勇陈鸿 MOE Key Laboratory of Advanced Micro-structured Materials School of Physics Sciences and EngineeringTongji UniversityShanghai 200092China Department of Electrical Engineering Tongji UniversityShanghai 201804China School of Automotive Studies Tongji UniversityShanghai 210804China

As one of the most attractive non-radiative power transfer mechanisms without cables,efficient magnetic resonance wireless power transfer(WPT)in the near field has been extensively developed in recent years,and promoted a variety of practical applications,such as mobile phones,medical implant devices and electric vehicles.However,the physical mechanism behind some key limitations of the resonance WPT,such as frequency splitting and size-dependent efficiency,is not very clear under the widely used circuit model.Here,we review the recently developed efficient and stable resonance WPT based on non-hermitian physics,which starts from a completely different avenue(utilizing loss and gain)to introduce novel functionalities to the resonance WPT.From the perspective of non-hermitian photonics,the coherent and incoherent effects compete and coexist in the WPT system,and the weak stable of energy transfer mainly comes from the broken phase associated with the phase transition of parity-time symmetry.Based on this basic physical framework,some optimization schemes are proposed,including using nonlinear effect,using bound states in the continuum,or resorting to the system with high-order parity-time symmetry.Moreover,the combination of non-hermitian physics and topological photonics in multi-coil system also provides a versatile platform for long-range robust WPT with topological protection.Therefore,the non-hermitian physics can not only exactly predict the main results of current WPT systems,but also provide new ways to solve the difficulties of previous designs.

关键词： wireless power transfer non-hermitian physics topological edge states

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Dynamical localization in a non-hermitian Floquet synthetic system

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Chinese physics B 2024年第5期33卷 147-151页

作者：可汗张嘉明霍良赵文垒 School of Science Jiangxi University of Science and TechnologyGanzhou 341000China School of Information Engineering Jiangxi University of Science and TechnologyGanzhou 341000China

We investigate the non-hermitian effects on quantum diffusion in a kicked rotor model where the complex kicking potential is quasi-periodically modulated in the time domain.The synthetic space with arbitrary dimension can be created by incorporating incommensurate frequencies in the quasi-periodical modulation.In the hermitian case,strong kicking induces the chaotic diffusion in the four-dimension momentum space characterized by linear growth of mean energy.We find that the quantum coherence in deep non-hermitian regime can effectively suppress the chaotic diffusion and hence result in the emergence of dynamical localization.Moreover,the extent of dynamical localization is dramatically enhanced by increasing the non-hermitian parameter.Interestingly,the quasi-energies become complex when the non-hermitian parameter exceeds a certain threshold value.The quantum state will finally evolve to a quasi-eigenstate for which the imaginary part of its quasi-energy is large most.The exponential localization length decreases with the increase of the non-hermitian parameter,unveiling the underlying mechanism of the enhancement of the dynamical localization by nonHermiticity.

关键词： Floquet system non-hermitian physics dynamical localization

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Topological bound state in the continuum induced unidirectional acoustic perfect absorption

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Science China(physics,Mechanics & Astronomy) 2023年第8期66卷 75-82页

作者： Haiyan Zhang Shanshan Liu Zhiwei Guo Shengyu Hu Yuguang Chen Yunhui Li Yong Li Hong Chen MOE Key Laboratory of Advanced Micro-structured Materials School of Physics Sciences and EngineeringTongji UniversityShanghai 200092China Institute of Acoustics Tongji UniversityShanghai 200092China Department of Electrical Engineering Tongji UniversityShanghai 201804China

The interaction between cavity field and atoms plays an important role in exploring the abundant non-hermitian physics and constructing powerful wave function devices.In this work,we propose theoretically and realize experimentally unidirectional perfect absorption in a non-hermitian acoustic system with the help of the topological bound state in the continuum(BIC),which is established by the hybrid interaction between one trivial BIC and another conventional resonant state.In the 2D parameter space spanned by frequency and distance between the two resonators,the topological scattering singularities appear in pairs and are associated with topological distinguished charges.Meanwhile,we reveal the origin of topological charges and their continuous evolution with the loss factor.At a specific loss factor,two topological charges just annihilate together,and acoustic perfect absorption induced by topological BIC is realized at the left incidence,while there is no phase singularity and near-total reflection is observed at the right incidence,hence the system presents extreme asymmetry.Our work bridges the gap between scattering characteristics of non-hermitian acoustic systems and topological scattering singularities,which may contribute to the research of novel non-hermitian physics and the practical applications of advanced absorbers and sensors.

关键词： non-hermitian physics topological scattering singularities bound state in the continuum unidirectional perfect absorption exceptional points

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Experimental realization of non-Abelian permutations in a three-state non-hermitian system

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National Science Review 2022年第11期9卷 79-86页

作者： Weiyuan Tang Kun Ding Guancong Ma Department of physics Hong Kong Baptist University Department of physics State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures(Ministry of Education) Fudan University

Eigenstates of a non-hermitian system exist on complex Riemannian manifolds, with multiple sheets connecting at branch cuts and exceptional points(EPs). These eigenstates can evolve across different sheets—a process that naturally corresponds to state permutation. Here, we report the first experimental realization of non-Abelian permutations in a three-state non-hermitian system. Our approach relies on the stroboscopic encircling of two different exceptional arcs(EAs), which are smooth trajectories of order-2EPs appearing from the coalescence of two adjacent states. The non-Abelian characteristics are confirmed by encircling the EAs in opposite sequences. A total of five non-trivial permutations are experimentally realized, which together comprise a non-Abelian group. Our approach provides a reliable way of investigating non-Abelian state permutations and the related exotic winding effects in non-hermitian systems.

关键词： non-Abelian permutation non-hermitian physics topological physics acoustics

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Interplay of nonreciprocity and nonlinearity on mean-field energy and dynamics of a Bose–Einstein condensate in a double-well potential

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Frontiers of physics 2022年第4期17卷 163-172页

作者： Yi-Piao Wu Guo-Qing Zhang Cai-Xia Zhang Jian Xu Dan-Wei Zhang Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials School of Physics and Telecommunication EngineeringSouth China Normal UniversityGuangzhou 510006China Guangdong–Hong Kong Joint Laboratory of Quantum Matter Frontier Research Institute for PhysicsSouth China Normal UniversityGuangzhou 510006China College of Electronics and Information Engineering Guangdong Ocean UniversityZhanjiang 524088China

We investigate the mean-field energy spectrum and dynamics in a Bose–Einstein condensate in a double-well potential with non-Hermiticity from the nonreciprocal hopping,and show that the interplay of nonreciprocity and nonlinearity leads to exotic properties.Under the two-mode and mean-field approximations,the nonreciprocal generalization of the nonlinear Schrödinger equation and Bloch equations of motion for this system are obtained.We analyze the PT phase diagram and the dynamical stability of fixed points.The reentrance of PT-symmetric phase and the reformation of stable fixed points with increasing the nonreciprocity parameter are found.Besides,we uncover a linear selftrapping effect induced by the nonreciprocity.In the nonlinear case,the self-trapping oscillation is enhanced by the nonreciprocity and then collapses in the PT-broken phase,and can finally be recovered in the reentrant PT-symmetric phase.

关键词： Bose–Einstein condensate non-hermitian physics nonlinear dynamics parity–time symmetry

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Exact solutions of non-hermitian chains with asymmetric long-range hopping under specific boundary conditions

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Chinese physics B 2022年第1期31卷 81-86页

作者：郭翠仙陈澍 Beijing National Laboratory for Condensed Matter physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Yangtze River Delta physics Research Center Liyang 213300China

We study the one-dimensional general non-hermitian models with asymmetric long-range hopping and explore how to analytically solve the systems under some specific boundary conditions.Although the introduction of long-range hopping terms prevents us from finding analytical solutions for arbitrary boundary parameters,we identify the existence of exact solutions when the boundary parameters fulfill some constraint relations,which give the specific boundary conditions.Our analytical results show that the wave functions take simple forms and are independent of hopping range,while the eigenvalue spectra display rich model-dependent structures.Particularly,we find the existence of a special point coined as pseudo-periodic boundary condition,for which the eigenvalues are the same as those of the periodical system when the hopping parameters fulfill certain conditions,whereas the eigenstates display the non-hermitian skin effect.

关键词： non-hermitian physics exact solution topological physics long-range hopping

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Real non-hermitian energy spectra without any symmetry

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Chinese physics B 2022年第7期31卷 1-7页

作者：张博学李青铔张笑李庆华 School of physics Sun Yat-sen UniversityGuangzhou 510275China Department of physics National University of SingaporeSingapore 117542Singapore

non-hermitian models with real eigenenergies are highly desirable for their stability.Yet,most of the currently known ones are constrained by symmetries such as PT-symmetry,which is incompatible with realizing some of the most exotic non-hermitian phenomena.In this work,we investigate how the non-hermitian skin effect provides an alternative route towards enforcing real spectra and system stability.We showcase,for different classes of energy dispersions,various ansatz models that possess large parameter space regions with real spectra,despite not having any obvious symmetry.These minimal local models can be quickly implemented in non-reciprocal experimental setups such as electrical circuits with operational amplifiers.

关键词： non-hermitian physics real energy spectra non-hermitian skin effect

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Two-body exceptional points in open dissipative systems

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Chinese physics B 2022年第1期31卷 51-55页

作者：丁霈泽易为 CAS Key Laboratory of Quantum Information University of Science and Technology of ChinaHefei 230026China CAS Center For Excellence in Quantum Information and Quantum physics Hefei 230026China

We study two-body non-hermitian physics in the context of an open dissipative system depicted by the Lindblad master equation.Adopting a minimal lattice model of a handful of interacting fermions with single-particle dissipation,we show that the non-hermitian effective Hamiltonian of the master equation gives rise to two-body scattering states with state-and interaction-dependent parity-time transition.The resulting two-body exceptional points can be extracted from the trace-preserving density-matrix dynamics of the same dissipative system with three atoms.Our results not only demonstrate the interplay of parity-time symmetry and interaction on the exact few-body level,but also serve as a minimal illustration on how key features of non-hermitian few-body physics can be probed in an open dissipative many-body system.

关键词： non-hermitian physics parity-time symmetry open system Lindblad equation

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Topological properties of non-hermitian Creutz ladders

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Chinese physics B 2022年第1期31卷 56-68页

作者：梁辉强李林虎 Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing&School of physics and Astronomy Sun Yat-Sen University(Zhuhai Campus)Zhuhai 519082China

We study topological properties of the one-dimensional Creutz ladder model with different non-hermitian asymmetric hoppings and on-site imaginary potentials,and obtain phase diagrams regarding the presence and absence of an energy gap and in-gap edge modes.The non-hermitian skin effect(NHSE),which is known to break the bulk-boundary correspondence(BBC),emerges in the system only when the non-Hermiticity induces certain unbalanced non-reciprocity along the ladder.The topological properties of the model are found to be more sophisticated than that of its hermitian counterpart,whether with or without the NHSE.In one scenario without the NHSE,the topological winding is found to exist in a two-dimensional plane embedded in a four-dimensional space of the complex Hamiltonian vector.The NHSE itself also possesses some unusual behaviors in this system,including a high spectral winding without the presence of long-range hoppings,and a competition between two types of the NHSE,with the same and opposite inverse localization lengths for the two bands,respectively.Furthermore,it is found that the NHSE in this model does not always break the conventional BBC,which is also associated with whether the band gap closes at exceptional points under the periodic boundary condition.

关键词： topological phases bulk-boundary correspondence non-hermitian physics Creutz ladders

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non-hermitian Kitaev chain with complex periodic and quasiperiodic potentials

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Chinese physics B 2021年第7期30卷 439-443页

作者：蒋相平乔艺曹俊鹏 Beijing National Laboratory for Condensed Matter physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical Sciences University of Chinese Academy of SciencesBeijing 100049China Songshan Lake Materials Laboratory Dongguan 523808China Peng Huanwu Center for Fundamental Theory Xian 710127China

We study the topological properties of the one-dimensional non-hermitian Kitaev model with complex either periodic or quasiperiodic potentials.We obtain the energy spectrum and the phase diagrams of the system by using the transfer matrix method as well as the topological invariant.The phase transition points are given analytically.The Majorana zero modes in the topological nontrivial regimes are obtained.Focusing on the quasiperiodic potential,we obtain the phase transition from the topological superconducting phase to the Anderson localization,which is accompanied with the Anderson localization–delocalization transition in this non-hermitian system.We also find that the topological regime can be reduced by increasing the non-Hermiticity.

关键词： non-hermitian physics Majorana zero modes transfer matrix

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