The conventional bulk-boundary correspondence directly connects the number of topological edge states in a finite system with the topological invariant in the bulk band structure with periodic boundary condition(PBC).However,recent studies show that this principle fails in certain non-Hermitian systems with broken reciprocity,which stems from the non-Hermitian skin effect(NHSE)in the finite system where most of the eigenstates decay exponentially from the system boundary.In this work,we experimentally demonstrate a 1D non-Hermitian topological circuit with broken reciprocity by utilizing the unidirectional coupling feature of the voltage follower module.The topological edge state is observed at the boundary of an open circuit through an impedance spectra measurement between adjacent circuit nodes.We confirm the inapplicability of the conventional bulk-boundary correspondence by comparing the circuit Laplacian between the periodic boundary condition(PBC)and open boundary condition(OBC).Instead,a recently proposed non-Bloch bulk-boundary condition based on a non-Bloch winding number faithfully predicts the number of topological edge states.
A digital-coding programmable metasurface(DCPM)is a type of functional system that is composed of subwavelength-scale digital coding elements with opposite phase responses.By configuring the digital coding elements,a DCPM can construct dynamic near-field image patterns in which the intensity of each pixel of the image can be dynamically and independently modulated.Thus,a DCPM can perform both spatial and temporal modulations.Here,this advantage is used to realize multichannel direct transmissions of near-field information.Three points are selected in the near-field region to form three independent channels.By applying various digital phase codes on the DCPM,independent binary digital symbols defined by amplitude codes(namely,weak and strong amplitudes)are transmitted through the three channels.The measured near-field distributions and temporal transmissions of the system agree with numerical calculations.Compared with the conventional multichannel transmission,the proposed mechanism achieves simultaneous spatial and temporal modulations by treating DCPM as an energy radiator and information modulator,thereby enduing DCPM with high potential in near-field information processing and communications.
Xiang WanQian ZhangTian Yi ChenLei ZhangWei XuHe HuangChao Kun XiaoQiang XiaoTie Jun Cui
Because of their exceptional capability to tailor the effective medium parameters,metamaterials have been widely used to control electromagnetic waves,which has led to the observation of many interesting phenomena,for example,negative refraction,invisibility cloaking,and anomalous reflections and transmissions.However,the studies of metamaterials or metasurfaces are mainly limited to their physical features;currently,there is a lack of viewpoints on metamaterials and metasurfaces from the information perspective.Here we propose to measure the information of a coding metasurface using Shannon entropy.We establish an analytical connection between the coding pattern of an arbitrary coding metasurface and its far-field pattern.We introduce geometrical entropy to describe the information of the coding pattern(or coding sequence)and physical entropy to describe the information of the far-field pattern of the metasurface.The coding metasurface is demonstrated to enhance the information in transmitting messages,and the amount of enhanced information can be manipulated by designing the coding pattern with different information entropies.The proposed concepts and entropy control method will be helpful in new information systems(for example,communication,radar and imaging)that are based on the coding metasurfaces.
We present a conformal metamaterial with simultaneous optical transparency and broadband millimeter-wave absorption for a curved surface. By tailoring the reflection response of meta-atoms at oblique angles, it is possible to achieve excellent absorption performance from 26.5 to 40.0 GHz within a wide angular range from 0° to 60°for transverse-electric and transverse-magnetic waves. In the meantime, by employing transparent substrates,including polyvinyl chloride and polyethylene terephthalate, good optical transmittance(80.1%) and flexibility are obtained simultaneously. The reflectivity of a curved metallic surface coated with the proposed curved metamaterial is simulated and measured experimentally. Both results demonstrate excellent absorption performance of the metamaterial, which is highly favored for practical applications.
CHENG ZHANGJIN YANGWENKANG CAOWEI YUANJUNCHEN KELIUXI YANGQIANG CHENGTIEJUN CUI
The terahertz region is a special region of the electromagnetic spectrum that incorporates the advantages of both microwaves and infrared light waves.In the past decade,metamaterials with effective medium parameters or gradient phases have been studied to control terahertz waves and realize functional devices.Here,we present a new approach to manipulate terahertz waves by using coding metasurfaces that are composed of digital coding elements.We propose a general coding unit based on a Minkowski closed-loop particle that is capable of generating 1-bit coding(with two phase states of 0 and 180°),2-bit coding(with four phase states of 0,90°,180°,and 270°),and multi-bit coding elements in the terahertz frequencies by using different geometric scales.We show that multi-bit coding metasurfaces have strong abilities to control terahertz waves by designing-specific coding sequences.As an application,we demonstrate a new scattering strategy of terahertz waves—broadband and wide-angle diffusion—using a 2-bit coding metasurface with a special coding design and verify it by both numerical simulations and experiments.The presented method opens a new route to reducing the scattering of terahertz waves.
Electromagnetic(EM)metamaterials are artificially engineered materials with extraordinary EM properties beyond the limit of existing nat-ural materials;thus,they have been widely used to manipulate the amplitude,phase,polarization,frequency,wave vector,waveform,and other degrees of freedom of EM waves in many practical applications.In this review,we will summarize recent advances in this flourishing field of EM metamateri-als,first from the perspectives of the classical regime and then the quantum regime.More specifically,in the classical regime,traditional EM metamate-rials are based on effective medium theory,and they have limitations of fixed functionalities and an inability to control EM waves in real time.To over-come these restrictions,information metamaterials,including digital coding and field-programmable metamaterials,have recently been proposed to en-able real-time manipulation of EM waves based on the theory of information science.By taking advantage of information metamaterials and artificial in-telligence,another crucial milestone of intelligent metamaterials has been achieved in the development of classical metamaterials.After overviewing EM metamaterials in the classical regime,we discuss cutting-edge studies of EM metamaterials in the quantum regime,namely,topological metamaterials and quantum metamaterials.These nonclassical metamaterials show excellent ability to flexibly manipulate the quantum states,and they extend the clas-sical information metamaterials into the field of quantum information science.At the end of this review,we will give some conclusions and perspectives on this fast-evolving field.
Jianwei YouQian MaLei ZhangChe LiuJianan ZhangShuo LiuTiejun Cui
In this review article, a brief introduction on the theory, experiments and applications of metamaterials is presented. The main focuses are concentrated on the composing meta-atoms, the method of transformation optics, the experimental demonstration of negative refraction, and the realizations of invisibility cloaks and electromagnetic black hole. At the end of this review, some typical applications of metamaterials, including high-performance antennas made of zero-refractive-index materials, inhomogeneous metamaterial lenses, and planar metasurfaces, are introduced in details.
Higher-order topological insulators(HOTIs)represent a new family of topological materials featuring quantized bulk polarizations and zero-dimensional corner states.In recent years,zero-dimensional corner states have been demonstrated in two-dimensional systems in the form of quadrupole modes or dipole modes.Due to the challenges in designing and constructing three-dimensional systems,octupole corner modes in 3D have not been observed.In this work,we experimentally investigate octupole topological phases in a three-dimensional electrical circuit,which can be viewed as a cubic lattice version of the Hofstadter model with aπ-flux threading each plaquette.We experimentally observe in our higher-order topological circuit a 0D corner state manifested as a localized impedance peak.The observed corner state in the electrical circuit is induced by the octupole moment of the bulk circuit and is topologically protected by anticommuting spatial symmetries of the circuit lattice.Our work provides a platform for investigating higher-order topological effects in three-dimensional electrical circuits.
Perfect lenses,superlenses and time-reversal mirrors can support and spatially separate evanescent waves,which is the basis for detecting subwavelength information in the far field.However,the inherent limitations of these methods have prevented the development of systems to dynamically distinguish subdiffraction-limited signals.Utilizing the physical merits of spoof surface plasmon polaritons(SPPs),we demonstrate that subdiffraction-limited signals can be transmitted on planar integrated SPP channels with low loss,low channel interference,and high gain and can be radiated with a very low environmental sensitivity.Furthermore,we show how deep subdiffraction-limited signals that are spatially coupled can be distinguished after line-of-sight wireless transmission.For a visualized demonstration,we realize the high-quality wireless communication of two movies on subwavelength channels over the line of sight in real time using our plasmonic scheme,showing significant advantages over the conventional methods.
Hao Chi ZhangLe Peng ZhangPei Hang HeJie XuCheng QianFrancisco J.Garcia-VidalTie Jun Cui
