Huanan Li

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Verified

Huanan verified their affiliation via an institutional email.

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• PhD
• Professor at Nankai University

Periodic structures with Bloch dispersion relation supporting a stationary inflection point (SIP) can display a unique scattering feature, the frozen mode regime (FMR). The FMR is much more robust than common cavity resonances; it is much less sensitive to the boundary conditions, structural imperfections, and losses. Using perturbation theory, we...

Wave absorption in time-invariant, passive thin films is fundamentally limited by a trade-off between bandwidth and overall thickness. In this work, we investigate the use of temporal switching to reduce signal reflections from a thin grounded slab over broader bandwidths. We extend quasi-normal mode theory to time switching, developing an ab initi...

Parity-time (PT) symmetry, satisfied when a system commutes under combined parity and time-reversal operations, enables extreme optical responses in non-Hermitian systems with balanced distributions of gain and loss. In this Letter, we propose a different path for PT symmetry utilizing the evanescent field excitation of anti-PT-symmetric structures...

Nonreciprocity is critically important in modern wave technologies, yet its general principles and practical implementations continue to raise intense research interest, in particular in the context of broken reciprocity based on spatiotemporal modulation. Abrupt changes in time of the electromagnetic properties of a material have also been shown t...

Time metamaterials offer a great potential for wave manipulation, drawing increasing attention in recent years. Here, we explore the exotic wave dynamics of an anisotropic photonic time crystal (APTC) formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix formalis...

Laser pulse compression serves as a pivotal technique in nonlinear optics and light-matter interactions. Traditional methods, including Q-switching, mode-locking techniques, and chirped pulse amplification, are employed to generate high-intensity fields. However, these methods pose challenges when applied to topological lasers. In this study, we ex...

Parity-time (PT) symmetry has enabled the demonstration of fascinating wave phenomena in non-Hermitian systems characterized by precisely balanced gain and loss. Until now, the exploration and observation of PT symmetry in scattering settings have largely been limited to propagating waves. Here, we demonstrate a versatile coupled-resonator acoustic...

Lorentzian-type media support optical phonons that oscillate with longitudinal polarization parallel to the wave direction, at a wave-vector-independent frequency at which the permittivity becomes zero. Here, we study the interactions between the longitudinal optical phonons and Lorentzian medium-based dispersive photonic time crystals (PTCs). We d...

By leveraging time interfaces and their combinations, time-switched metamaterials facilitate efficient wave manipulation in a uniform medium, circumventing energy conservation during propagation. Here, by merging time interfaces with magnetized Lorentz material dispersion, we demonstrate that a time-switched magneto-optical medium can enable the ge...

Lorentzian-type media support optical phonons that oscillate with longitudinal polarization parallel to the wave direction, at a wave vector-independent frequency at which the permittivity becomes zero. Here, we study the interactions between the longitudinal optical phonons and Lorentzian medium-based dispersive photonic time crystals (PTCs). We d...

Photonic time crystals (PTCs) host momentum bandgaps enabling intriguing non-resonant light amplification in propagating waves, but opening substantial bandgaps demands refractive index changes too extreme for conventional nonlinear optics. Here, we introduce momentum bandgaps for non-uniform waves, including evanescent and ghost types, by extendin...

Double-slit experiments, wherein light passes through a thin subwavelength or near-wavelength double slit, have confirmed the wave-particle duality of many quantum entities. Recently, it has been reported that the double-slit time diffraction of light upon twice gated in time produces the frequency diffraction. Here, we present a collinear intermod...

Double-slit experiments, wherein light passes through a thin subwavelength or near-wavelength double slit, have confirmed the wave-particle duality of many quantum entities. Recently, it has been reported that the double-slit time diffraction of light upon twice gated in time produces the frequency diffraction. Here, we present a collinear intermod...

Spectral singularities (SSs) emerge at isolated real frequencies when the scattering coefficients of a system diverge, producing scattering anomalies in non-Hermitian systems. Here, based on parity-time symmetry, we introduce SSs for evanescent waves, and explore their exotic features. We show that evanescent wave SSs can realize highly reconfigura...

Non-Hermitian wave engineering has attracted a surge of interest in photonics in recent years. Prominent non-Hermitian phenomena include coherent perfect absorption and its generalization, reflectionless scattering modes, in which electromagnetic scattering at the input ports is suppressed due to critical coupling with the power leaked to output po...

Faraday rotation is one of the most classical ways to realize nonreciprocal photonic devices like optical isolators. Recently, the temporal analog of Faraday rotation, achieved through time-interfaces, was introduced [H. Li, S. Yin, and A. Alù, Phys. Rev. Lett. 128, 173901 (2022)]. Here, we extend this concept to the periodic switching regime by in...

We experimentally demonstrate chaotic coherent perfect absorption states, as well as their non-Hermitian degeneracies in a chaotic optical microresonator supporting more than 1000 optical modes.

Non-Hermitian wave engineering has attracted a surge of interest in photonics in recent years. One of the prominent phenomena is coherent perfect absorption (CPA), in which the annihilation of electromagnetic scattering occurs by destructive interference of multiple incident waves. This concept has been implemented in various platforms to demonstra...

Time metamaterials exhibit a great potential for wave manipulation, drawing increasing attention in recent years. Here, we explore the exotic wave dynamics in an anisotropic photonic time crystal (APTC), formed by an anisotropic medium whose optical properties are uniformly and periodically changed in time. Based on a temporal transfer matrix forma...

Coupled resonances in non‐Hermitian systems can lead to exotic optical features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been recently emerged as powerful tools to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineer spatial wavefronts have remained elu...

Time-varying media have recently emerged as a new paradigm for wave manipulation, due to the synergy between the discovery of highly nonlinear materials, such as epsilon-near-zero materials, and the quest for wave applications, such as magnet-free nonreciprocity, multimode light shaping, and ultrafast switching. In this review, we provide a compreh...

Time-varying media have recently emerged as a new paradigm for wave manipulation, thanks to thesynergy between the discovery of novel, highly nonlinear materials, such as epsilon-near-zero materials, and the questfor novel wave applications, such as magnet-free nonreciprocity, multi-mode light shaping, and ultrafast switching. Inthis review we prov...

Temporal interfaces introduced by abrupt switching of the constitutive parameters of unbounded media enable unusual wave phenomena. So far, their explorations have been mostly limited to lossless media. Yet, non-Hermitian phenomena leveraging material loss and gain, and their balanced combination in parity-time (PT)-symmetric systems, have been ope...

Resonance coupling in non-Hermitian systems can lead to exotic features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been widely employed to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineering spatial wavefronts have remained elusive. Here, we show that...

Temporal interfaces introduced by abrupt switching of the constitutive parameters of unbounded media enable unusual wave phenomena. So far, their explorations have been mostly limited to lossless media. Yet, non-Hermitian phenomena leveraging material loss and gain, and their balanced combination in parity-time (PT)-symmetric systems, have been ope...

We numerically implement the concept of thermal radiation pumps in realistic photonic circuits and demonstrate their efficiency to control the radiation current, emitted between two reservoirs with equal temperature. The proposed pumping scheme involves a cyclic adiabatic modulation of two parameters that control the spectral characteristics of the...

Electrically small antennas are characterized by large quality factors, which yield limited gain-bandwidth products, as a result of the Bode-Fano limit. This bound implies a trade-off between the antenna’s footprint and radiation features, hindering wireless applications that require compact, broadband, and efficient antennas. Here, building on a p...

By using Floquet driving protocols and interlacing them with a judicious reservoir emission engineering, we achieve extreme nonreciprocal thermal radiation. We show that the latter is rooted in an interplay between a direct radiation process occurring due to temperature bias between two thermal baths and the modulation process that is responsible f...

Subwavelength nanostructures with tunable compositions and geometries show favorable optical functionalities for the implementation of nanophotonic systems. Precise and versatile control of structural configurations on solid substrates is essential for their applications in on-chip devices. Here, we report all-solid-phase reconfigurable chiral nano...

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Wave absorption in time-invariant, passive thin films is fundamentally limited by a trade-off between bandwidth and overall thickness. In this work, we investigate the use of temporal switching to reduce signal reflections from a thin grounded slab over broader bandwidths. We extend quasi-normal mode theory to time switching, developing an ab initi...

We leverage aperiodic temporal modulations and nonreciprocity to realize PT-symmetric phenomena without the need for gain and loss provided by external mechanisms. We develop our approach using a general coupled-mode framework, and verify our results via detailed simulations in a conservative electronic circuit, demonstrating wave phenomena such as...

We develop, within a near-field thermal radiation framework, a Floquet scattering approach that establishes a reconfigurable control of the direction of thermal radiation between reservoirs. The method promotes a connection with Floquet engineering -- originally developed in many-body physics -- thus allowing us to design periodically driven photon...

Integrating multiple functionalities into a single metasurface is becoming of great interest for future intelligent communication systems. While such devices have been extensively explored for reciprocal functionalities, in this work, we integrate a wide variety of nonreciprocal applications into a single platform. The proposed structure is based o...

Scattering processes are typically sensitive to the incident wave properties and to interference effects generated via wave-matter interactions with the target. We challenge this general belief in the case of targets that undergo time-periodic modulations encircling quasiadiabatically an exceptional point in a given parameter space. When the scatte...

The scattering of electromagnetic waves lies at the heart of most experimental techniques over nearly the entire electromagnetic spectrum, ranging from radio waves to optics and x rays. Hence, deep insight into the basics of scattering theory and an understanding of the peculiar features of electromagnetic scattering are necessary for the correct i...

Parity-time (PT) symmetry has been opening exciting opportunities in optics, yet the required careful balance of loss and gain has been hindering its practical implementations. Here, we propose a gain-free route to PT-symmetry based on non-monochromatic excitations that mimic loss and gain in passive systems. Based on the concept of virtual absorpt...

Parity-time (PT) symmetry has been opening exciting opportunities in optics, yet the required careful balance of loss and gain has been hindering its practical implementations. Here, we propose a gain-free route to PT-symmetry based on non-monochromatic excitations that mimic loss and gain in passive systems. Based on the concept of virtual absorpt...

Scattering of electromagnetic waves lies at the heart of most experimental techniques over nearly the entire electromagnetic spectrum, ranging from radio waves to optics and X-rays. Hence, deep insight into the basics of scattering theory and understanding the peculiar features of electromagnetic scattering is necessary for the correct interpretati...

Integrating multiple functionalities into a single metasurface is becoming of great interest for future intelligent communication systems. While such devices have been extensively explored for reciprocal functionalities, in this work, we integrate a wide variety of nonreciprocal applications into a single platform. The proposed structure is based o...

An exceptional point (EP) is a non-Hermitian degeneracy where both eigenvalues and their corresponding eigenvectors coalesce. It was recently proposed and demonstrated that such spectral singularity can be utilized for enhanced sensing. Potential drawbacks of EP sensing include both fundamental resolution limit and noise effects that might mask the...

Chu’s limit determines the minimum radiation quality factor Q of an electrically small resonator, and hence its maximum operational bandwidth, which is inversely proportional to its volume. This bound imposes severe restrictions in several areas of technology, from wireless communications to nanophotonics and metamaterials. We show that a suitably...

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an instantaneous scattering matrix approach to unveil the critical role of wave in...

Scattering of electromagnetic waves lies at the heart of most experimental techniques over nearly the entire electromagnetic spectrum, ranging from radio waves to optics and X-rays. Hence, deep insight into the basics of scattering theory and understanding the peculiar features of electromagnetic scattering is necessary for the correct interpretati...

We control the direction and magnitude of thermal radiation, between two bodies at equal temperature (in thermal equilibrium), by invoking the concept of adiabatic pumping. Specifically, within a resonant near-field electromagnetic heat transfer framework, we utilize an {\it instantaneous} scattering matrix approach to unveil the critical role of w...

We employ renormalization ideas in order to describe the interplay between a frozen mode regime—a scattering feature associated with the presence of stationary inflection point (SIP) singularities—and disorder in photonic systems. Specifically, we demonstrate the existence of a -function for a (rescaled) Wigner delay time at SIP frequencies which d...

We utilize an effective Hamiltonian formalism, within the Floquet scattering framework, to design a class of driving-induced nonreciprocal components with minimal complexity. In the high-driving-frequency limit, where our scheme is formally applicable, these designs demonstrate a leading-order nonreciprocal performance that is inversely proportiona...

We introduce the concept of multichannel dynamically modulated perfect absorbers (DMPAs), which are periodically modulated lossy interferometric traps that completely absorb incident monochromatic waves. The proposed DMPA protocols utilize a Floquet engineering approach which produces a variety of emerging phenomena and features: reconfigurability...

We analyze coherent wave transport in a new physical setting associated with multimode wave systems where reflection is completely suppressed and mode-dependent losses together with mode mixing are dictating the wave propagation. An additional physical constraint is the fact that in realistic circumstances the access to the scattering (or transmiss...

We utilize an effective Hamiltonian formalism, within the Floquet scattering framework, to design a class of driving-induced non-reciprocal components with {\it minimal} complexity. In the high driving-frequency limit, where our scheme is formally applicable, these designs demonstrate a leading order non-reciprocal performance which is inverse prop...

The design of time-independent effective Hamiltonians that describe periodically modulated systems, provides a promising approach to realize new forms of matter. This, so-called, Floquet engineering approach is currently limited to the description of wavepacket dynamics. Here, we utilize the notion of effective Hamiltonians and develop a Floquet en...

The design of time-independent effective Hamiltonians that describe periodically modulated systems provides a promising approach to realize new forms of matter. This so-called Floquet engineering approach is currently limited to the description of wave-packet dynamics. Here, we utilize the notion of effective Hamiltonians and develop a Floquet engi...

We introduce the concept of multichannel Floquet Perfect Absorbers (FPAs) which are periodically modulated lossy interferometric traps that completely absorb incident monochromatic waves. The proposed FPA protocols utilize a Floquet engineering approach which inflicts a variety of emerging phenomena and features: reconfigurability of perfect absorp...

We develop a statistical theory of waveform shaping of incident waves that aims to efficiently deliver energy at weakly lossy targets which are embedded inside chaotic or weakly disordered enclosures such as body cavities, buildings, vessels, etc. Our approach utilizes the universal features of chaotic scattering, thus minimizing the use of informa...

We analyze coherent wave transport in a new physical setting associated with multimode wave systems where reflection is completely suppressed and mode-dependent losses together with mode-mixing are dictating the wave propagation. An additional physical constraint is the fact that in realistic circumstances the access to the scattering (or transmiss...

We develop a theoretical framework that lays out the fundamental rules under which a periodic (Floquet) driving scheme can induce nonreciprocal transport. Our approach utilizes an extended Hilbert space where a Floquet network with an extra (frequency) dimension naturally arises. The properties of this network (its on-site potential and the intersi...

Many novel concepts in \(\mathcal {PT}\)-symmetric wave transport were initially explored and demonstrated in the conceptually simpler and experimentally more accessible framework of active electronic circuits. These include eigenmode analysis and spatio-temporal dynamics of the stored energy in static and in periodically driven (Floquet) \(\mathca...

We develop a statistical theory of waveform shaping of incident waves that aim to efficiently deliver energy at weakly lossy targets which are embedded inside chaotic enclosures. Our approach utilizes the universal features of chaotic scattering -- thus minimizing the use of information related to the exact characteristics of the chaotic enclosure....

We introduce the notion of adiabatic state-flip of a Floquet Hamiltonian associated with a non-Hermitian system that it is subjected to two driving schemes with clear separation of time scales. The fast (Floquet) modulation scheme is utilized to re-allocate the exceptional points in the parameter space of the system and re-define the topological fe...

We introduce the notion of adiabatic state-flip of a Floquet Hamiltonian associated with a non-Hermitian system that it is subjected to two driving schemes with clear separation of time scales. The fast (Floquet) modulation scheme is utilized to re-allocate the exceptional points in the parameter space of the system and re-define the topological fe...

We develop a theoretical framework that lay out the fundamental rules under which a periodic (Floquet) driving scheme can induce non-reciprocal transport. Our approach relies on the formulation of the Floquet problem in the extended Hilbert space, when a Floquet lattice with an extra (frequency) dimension naturally arises. The properties of this la...

Periodic structures with Bloch dispersion relation supporting a stationary inflection point (SIP) can display a unique scattering feature, the frozen mode regime (FMR). The FMR is much more robust than common cavity resonances; it is much less sensitive to the boundary conditions, structural imperfections, and losses. Using perturbation theory, we...

We propose a new driving scheme, when different parts of a system are driven with different, generally incommensurate, frequencies. Such driving provides a flexible handle to control various properties of the system and to obtain new types of effective (static) Hamiltonians with arbitrary static on-site potential, be it deterministic or random. Thi...

We propose a new driving scheme, when different parts of a system are driven with different, generally incommensurate, frequencies. Such driving provides a flexible handle to control various properties of the system and to obtain new types of effective (static) Hamiltonians with arbitrary static on-site potential, be it deterministic or random. Thi...

We provide an experimental framework where periodically driven PT-symmetric systems can be investigated. The set-up, consisting of two UHF oscillators coupled by a time-dependent capacitance, demonstrates a cascade of PT-symmetric broken domains bounded by exceptional point degeneracies. These domains are analyzed and understood using an equivalent...

We provide an experimental framework where periodically driven PT-symmetric systems can be investigated. The set-up, consisting of two UHF oscillators coupled by a time-dependent capacitance, demonstrates a cascade of PT-symmetric broken domains bounded by exceptional point degeneracies. These domains are analyzed and understood using an equivalent...

We show that gyrotropic structures with balanced gain and loss that respect anti-linear symmetries exhibit a giant non-reciprocity at the so-called exact phase where the eigenfrequencies of the isolated non-Hermitian set-up are real. The effect occurs in a parameter domain near an exceptional point (EP) degeneracy, where mode-orthogonality collapse...

We employ Random Matrix Theory in order to investigate coherent perfect absorption (CPA) in lossy systems with complex internal dynamics. The loss strength $\gamma_{\rm CPA}$ and energy $E_{\rm CPA}$, for which a CPA occurs are expressed in terms of the eigenmodes of the isolated cavity -- thus carrying over the information about the chaotic nature...

We employ Random Matrix Theory in order to investigate coherent perfect absorption (CPA) in lossy systems with complex internal dynamics. The loss strength $\gamma_{\rm CPA}$ and energy $E_{\rm CPA}$, for which a CPA occurs are expressed in terms of the eigenmodes of the isolated cavity -- thus carrying over the information about the chaotic nature...

We show that gyrotropic structures with balanced gain and loss that respect antilinear symmetries exhibit a giant nonreciprocity at the so-called exact phase where the eigenfrequencies of the isolated non-Hermitian setup are real. The effect occurs in a parameter domain near an exceptional- point (EP) degeneracy, where mode orthogonality collapses....

There exists an analogy between Maxwell equations in a rotating frame and Schr\"odinger equation for a charged particle in the presence of a magnetic field. We exploit this analogy to point out that electromagnetic phenomena in the rotating frame, under appropriate conditions, can exhibit periodicity with respect to the angular velocity of rotation...

There exists an analogy between Maxwell equations in a rotating frame and Schr\"odinger equation for a charged particle in the presence of a magnetic field. We exploit this analogy to point out that electromagnetic phenomena in the rotating frame, under appropriate conditions, can exhibit periodicity with respect to the angular velocity of rotation...

We investigate the transport characteristics of a four-port gyrotropic photonic structure with mirror-time reversal symmetry. The structure consists of two coupled cavities with balanced amplification and attenuation. The cavities are placed on top of a gyrotropic substrate and are coupled to two bus waveguides. Using detail simulations in the micr...

We demonstrate that a three-terminal harmonic symmetric chain in the presence of a Coriolis force, produced by a rotating platform which is used to place the chain, can produce thermal rectification. The direction of heat flow is reconfigurable and controlled by the angular velocity $\Omega$ of the rotating platform. A simple three terminal triangu...

We demonstrate that a three-terminal harmonic symmetric chain in the presence of a Coriolis force, produced by a rotating platform which is used to place the chain, can produce thermal rectification. The direction of heat flow is reconfigurable and controlled by the angular velocity $\Omega$ of the rotating platform. A simple three terminal triangu...

We propose a family of {\it local} $\cal{PT}$-symmetric photonic lattices with transverse index gradient $\omega$, where the emergence of {\it stable} Bloch-Zener oscillations are controlled by the degree of non-Hermiticity $\gamma$ of the lattice. In the exact $\cal{PT}$-symmetric phase we identify a condition between $\omega$ and $\gamma$ for whi...

We investigate sound propagation in a moving fluid confined in a randomly corrugated tube. For weak randomness and small fluid velocities $v^{(0)}$, the localization length $\xi$ shows extreme sensitivity to the variation of $v^{(0)}$. In the opposite limit of large fluid velocities, $\xi$ acquires a constant value which is independent of the frequ...

We analytically investigate the heat current $I$ and its thermal fluctuations $\Delta$ in a branching network without loops (Cayley tree). The network consists of two type of harmonic masses: vertex masses $M$ placed at the branching points where phononic scattering occurs and masses $m$ at the bonds between branching points where phonon propagatio...

We show that the presence of a Coriolis force in a rotating linear lattice imposes a non-reciprocal propagation of the phononic heat carriers. Using this effect we propose the concept of Coriolis linear thermal circulator which can control the circulation of a heat current. A simple model of three coupled harmonic masses on a rotating platform allo...

We study full counting statistics for transferred heat and entropy production between multi-terminal systems in absence of a finite junction. The systems are modelled as collections of coupled harmonic oscillators which are kept at different equilibrium temperatures and are connected via arbitrary time dependent couplings. Following consistent quan...

This review deals with the nonequilibrium Green's function (NEGF) method applied to the problems of energy transport due to atomic vibrations (phonons), primarily for small junction systems. We present a pedagogical introduction to the subject, deriving some of the well-known results such as the Laudauer-like formula for heat current in ballistic s...

We consider thermal conduction across a general nonlinear phononic junction. Based on two-time observation protocol and the field theoretical/algebraic method, the cumulants of the heat transferred in both transient and steady-state regimes are studied on an equal footing, and practical formulae for the calculation of the cumulant generating functi...

We study the transport of energy in a finite linear harmonic chain by solving the Heisenberg equation of motion, as well as by using nonequilibrium Green's functions to verify our results. The initial state of the system consists of two separate and finite linear chains that are in their respective equilibriums at different temperatures. The chains...

Based on two-time observation protocol, we consider heat transfer in a given time interval $t_{M}$ in lead-junction-lead system taking coupling between the leads into account. In view of the two-time observation, consistency conditions are carefully verified in our specific family of quantum histories. Furthermore, its implication is briefly explor...

We present a generalized transmission coefficient formula for the lead-junction-lead system, in which interaction between the leads has been taken into account. Based on it the Caroli formula could be easily recovered and a transmission coefficient formula for interface problem in the ballistic system can be obtained. The condition of validity for...