Sensors play a crucial role in advanced apparatuses and it is persistently pursued to improve their sensitivities. Recently, the singularity of a non-Hermitian system, known as the exceptional point (EP), has drawn much attention for this goal. Response of the eigenfrequency shift to a perturbation $\epsilon$ follows the $\epsilon^{1/n}$-dependence at an $n$th-order EP, leading to significantly enhanced sensitivity via a high-order EP. However, due to the requirement of increasingly complicated systems, great difficulties will occur along the path of increasing the EP order to enhance the sensitivity. Here we report that by utilizing the spectral anomaly of the coherent perfect absorption (CPA), the sensitivity at a third-order EP can be further enhanced owing to the cooperative effects of both CPA and EP. We realize this synthetically enhanced sensor using a pseudo-Hermitian cavity magnonic system composed of two yttrium iron garnet spheres and a microwave cavity. The detectable minimum change of the magnetic field reaches $4.2\times10^{-21}$T. It opens a new avenue to design novel sensors using hybrid non-Hermitian quantum systems.

Different from traditional organic luminescent materials based on covalent delocalization, clusteroluminescence from nonconjugated luminogens relies on noncovalent through-space conjugation of electrons. However, such spatial electron delocalization is usually weak, resulting in low luminescent efficiency and board emission peak due to multiple vibrational energy levels. Herein, several nonconjugated luminogens are constructed by employing biphenyl as the building unit to reveal the structure-property relationship and solve current challenges. The intramolecular through-space conjugation can be gradually strengthened by introducing building units and stabilized by rigid molecular skeleton and multiple intermolecular interactions. Surprisingly, narrowband clusteroluminescence with full width at half-maximum of 40 nm and 100% efficiency is successfully achieved via an asymmetric conformation, exhibiting comparable performance to the traditional conjugated luminogens. This work realizes highly efficient and narrowband clusteroluminescence from nonconjugated luminogens and highlights the essential role of structural conformation in manipulating the photophysical properties of unconventional luminescent materials. Clusteroluminescence from nonconjugated luminogens relies on noncovalent through-space conjugation of electrons resulting in low luminescent efficiency and broad emission. Here the authors construct several nonconjugated luminogens to reveal the structure property relationship and demonstrate narrowband clusteroluminescence with high emission efficiency.

Synchronization and asynchronization are ubiquitous occurrences in a wide range of natural and artificial systems. The underlying mechanisms responsible for these events are typically complex, presenting a considerable difficulty to grasp the crucial elements that cause synchronization or asynchronization. Moreover, real-world systems frequently encounter energy exchanges with their surrounding environment; synchronization and asynchronization in such non-Hermitian systems have not been fully understood. In this work, we study the synchronization and asynchronization phenomena in a simple non-Hermitian system that involves two coupled bosonic modes. We find that such an open system evolves towards a state of lower dissipation as it synchronizes, whereby the existence of particular symmetries, such as anti-parity-time (anti-PT) symmetry and PT symmetry, impact synchronization. Peculiarly, we show that when the anti-PT symmetry is broken or the PT symmetry is unbroken, a state of asynchronization occurs as the result of the degeneracy of imaginary parts of the eigenvalues. We designate this occurrence as "degeneracy-induced asynchronization." Our findings shed light on generating and controlling synchronization and asynchronization in non-Hermitian systems.

Entanglement is a fundamental property in quantum mechanics that systems share inseparable quantum correlation regardless of their mutual distances. Owing to the fundamental significance and versatile applications, the generation of quantum entanglement between macroscopic systems has been a focus of current research. Here we report on the deterministic generation and tomography of the macroscopically entangled Bell state in a hybrid quantum system containing a millimeter-sized spin system (∼ 1×10^19 atoms) and a micrometer-sized superconducting qubit. The deterministic generation is realized by coupling the macroscopic spin system and the qubit via a microwave cavity. Also, we develop a joint tomography approach to confirming the deterministic generation of the Bell state, which gives a generation fidelity of 0.90±0.01. Our work makes the macroscopic spin system the largest system (in the sense of atom number) capable of generating the maximally entangled quantum state.

Quantum computing, quantum communication, and quantum networks rely on hybrid quantum systems operating in different frequency ranges. For instance, the superconducting qubits work in the gigahertz range, while the optical photons used in communication are in the range of hundreds of terahertz. Due to the large frequency mismatch, achieving the direct coupling and information exchange between different information carriers is generally difficult. Accordingly, a quantum interface is demanded, which serves as a bridge to establish information linkage between different quantum systems operating at distinct frequencies. Recently, the magnon mode in ferromagnetic spin systems has received significant attention. While the inherent weak optomagnonic coupling strength restricts the microwave-to-optical photon conversion efficiency using magnons, the versatility of the magnon modes, together with their readily achievable strong coupling with other quantum systems, endow them with many distinct advantages. Here, the magnon-based microwave-light interface is realized by adopting an optical cavity with adjustable free spectrum range and different kinds of magnetostatic modes in two microwave cavity configurations. By optimizing the parameters, a conversion efficiency of 1.75x10-8$1.75\times 10<^>{-8}$ with bandwidth of 24 MHz is achieved. The impact of various parameters on the microwave-to-optics conversion is analyzed. The study provides useful guidance and insights to further enhancing the microwave-to-optics conversion efficiency using magnons. This work explores microwave-to-optics conversion using spin-wave modes coupled with a tunable free spectral range Fabry-P & eacute;rot cavity. By leveraging magnon-induced Brillouin scattering and the adjustable cavity, the system enables efficient transduction between telecom photons and microwaves across a tunable frequency range. This approach holds promise for advancing quantum information processing, bridging microwave and optical domains for hybrid quantum technologies. image

Time-varying media break the temporal translation symmetry of wave propagation in materials, enabling advanced wave manipulations. However, this novel phenomenon has been rarely explored in magnonic systems due to the significant challenge of achieving a sudden and prominent change in magnon dispersion within materials. Here, we construct a time-varying strong coupling between two magnon modes, and observe a change in the beats of Rabi-like oscillations near the pulse edges. Using a frequency-comb spectroscopy technique developed in this work, we characterize the frequency conversion of magnon modes induced by the time-varying strong-coupling effect. Moreover, we construct time slits with adjacent time interfaces and demonstrate, for the first time, the double-slit time diffraction of magnon modes, analogous to the well-known Young's double-slit experiment. These findings rely solely on the time-varying strong magnon coupling, independent of device reconfiguration. Our results open avenues for applications such as all-magnetic mixers or on-chip GHz sources.

Light-matter interaction is crucial to both understanding fundamental phenomena and developing versatile applications. Strong coupling, robustness, and controllability are the three most important aspects in realizing light-matter interactions. Topological and non-Hermitian photonics have provided frameworks for robustness and control flexibility, respectively. How to engineer the properties of the edge state such as photonic density of state by using non-Hermiticity while ensuring topological protection has not been fully studied. Here we construct a parity-time-symmetric dimerized photonic lattice and probe the spontaneous $PT$-symmetry breaking of the edge states by utilizing the strong coupling between the photonic mode and a spin ensemble. Our Letter presents an accurate and almost noninvasive approach for investigating non-Hermitian topological states, while also offering methodologies for the implementation and manipulation of topological light-matter interactions.

With their incomparable time-frequency accuracy, frequency combs have significantly advanced precision spectroscopy, ultra-sensitive detection, and atomic clocks. Traditional methods to create photonic, phononic, and magnonic frequency combs hinge on material nonlinearities which are often weak, necessitating high power densities to surpass their initiation thresholds, which subsequently limits their applications. Here, we introduce a novel nonlinear process to efficiently generate magnonic frequency combs (MFCs) by exploiting exceptional points (EPs) in a coupled system comprising a pump-induced magnon mode and a Kittel mode. Even without any cavity, our method greatly improves the efficiency of nonlinear frequency conversion and achieves optimal MFCs at low pump power. Additionally, our novel nonlinear process enables excellent tunability of EPs using the polarization and power of the pump, simplifying MFC generation and manipulation. Our work establishes a synergistic relationship between non-Hermitian physics and MFCs, which is advantages for coherent/quantum information processing and ultra-sensitive detection.

AbstractThrough‐space interaction (TSI) has been proven to play an important role in the newly emerging clusteroluminescence (CL) phenomenon. However, it is still a big challenge to manipulate the TSI at the molecular level due to the unclear relationship between the non‐conjugated structure and TSI properties. Herein, the TSI in diphenylmethane is manipulated by breaking its symmetric structures and changing the isolated subunits. Finally, the CL wavelength and efficiency of diphenylmethane are successfully regulated at the aggregate state.

Nonlinear magnonics studies the nonlinear interaction between magnons and other physical platforms (phonon, photon, qubit, spin texture) to generate novel magnon states for information processing. In this Tutorial, we first introduce the nonlinear interactions of magnons in pure magnetic systems and hybrid magnon–phonon and magnon–photon systems. Then, we show how these nonlinear interactions can generate exotic magnonic phenomena. In the classical regime, we will cover the parametric excitation of magnons, bistability and multistability, and magnonic frequency comb. In the quantum regime, we will discuss the single-magnon state, Schrödinger cat state, and the entanglement and quantum steering among magnons, photons, and phonons. The applications of the hybrid magnonics systems in quantum transducer and sensing will also be presented. Finally, we look at the future development direction of nonlinear magnonics.

Nonclassical quantum states are the pivotal features of a quantum system that differs from its classical counterpart. However, the generation and coherent control of quantum states in a macroscopic spin system remain an outstanding challenge. Here we experimentally demonstrate the quantum control of a single magnon in a macroscopic spin system (i.e., 1 mm-diameter yttrium-iron-garnet sphere) coupled to a superconducting qubit via a microwave cavity. By tuning the qubit frequency in situ via the Autler-Townes effect, we manipulate this single magnon to generate its nonclassical quantum states, including the single-magnon state and the superposition of single-magnon state and vacuum (zero magnon) state. Moreover, we confirm the deterministic generation of these nonclassical states by Wigner tomography. Our experiment offers the first reported deterministic generation of the nonclassical quantum states in a macroscopic spin system and paves a way to explore its promising applications in quantum engineering.

Light-matter interaction is crucial to both understanding fundamental phenomena and developing versatile applications. Strong coupling, robustness, and controllability are the three most important aspects in realizing light-matter interactions. Topological and non-Hermitian photonics, have provided frameworks for robustness and extensive control freedom, respectively. How to engineer the properties of the edge state such as photonic density of state, scattering parameters by using non-Hermitian engineering while ensuring topological protection has not been fully studied. Here we construct a parity-time-symmetric dimerized photonic lattice and generate complex-valued edge states via spontaneous PT-symmetry breaking. The enhanced strong coupling between the topological photonic edge mode and magnon mode in a ferromagnetic spin ensemble is demonstrated. Our research reveals the subtle non-Hermitian topological edge states and provides strategies for realizing and engineering topological light-matter interactions.

We experimentally demonstrate the nonreciprocal microwave amplification using a cavity magnonic system, consisting of a passive cavity (i.e., the split-ring resonator), an active feedback circuit integrated with an amplifier, and a ferromagnetic spin ensemble (i.e., a yttrium-iron-garnet sphere). Combining the amplification provided by the active circuit and the nonreciprocity supported by the cavity magnonics, we implement a nonreciprocal amplifier with the functions of both unidirectional amplification and reverse isolation. The microwave signal is amplified by 11.5 dB in the forward propagating direction and attenuated in the reverse direction by -34.7 dB, giving an isolation ratio of 46.2 dB. Such a unidirectional amplifier can be readily employed in quantum technologies, where the device can simultaneously amplify the weak signal output by the quantum system and isolate the sensitive quantum system from the backscattered external noise. Also, it is promising to explore more functions and applications using a cavity magnonic system with real gain.

Building hybrid quantum systems is a crucial step for realizing multifunctional quantum technologies, quantum information processing, and hybrid quantum networks. A functional hybrid quantum system requires strong coupling among its components. However, couplings between distinct physical systems are typically very weak. Experimental realization of strong coupling in a hybrid system remains a long-standing challenge, especially when it has multiple components and the components are of different nature. Here we demonstrate the realization of triple strong coupling in a novel polaromechanical hybrid system, where polaritons, formed by strongly coupled ferromagnetic magnons and microwave photons, are further strongly coupled to phonons. The corresponding polaromechanical normal-mode splitting is observed. A high polaromechanical cooperativity of 9.4×10^3 is achieved by significantly reducing the polariton decay rate via exploiting coherent perfect absorption. The quantum cooperativity much greater than unity is achievable if placing the system at cryogenic temperatures, which would enable various quantum applications. Our results pave the way towards coherent quantum control of photons, magnons and phonons, and are a crucial step for building functional hybrid quantum systems based on magnons.

Nonconjugated clusteroluminogens (CLgens) become increasingly important in photophysics and advanced bioelectronic applications. Most CLgens show ultraviolet emission, and it remains an enormous challenge to change the electronic structures of CLgens to improve their photophysical properties by precisely regulating the intramolecular through-space interactions (TSI). Herein we propose a general strategy to construct a higher-level intramolecular TSI in multiaryl-substituted alkanes, namely the secondary through-space interaction (2nd TSI), which is constructed by the primary through-space interaction (1st TSI) and TSI linker. By introducing methyl and phenyl into 1,1,3,3-tetraphenylpropane (TPP) respectively, butane-1,1,3,3-tetrayltetrabenzene (Me-TPP) and propane-1,1,1,3,3-pentaylpentabenzene (Ph-TPP) both show bright visible clusteroluminescence (CL), whose fluorescence quantum yield is up to ~40% and the emission wavelength extends to 530 nm. Advanced theoretical studies relating to their emission mechanism are quantitatively performed to analyze the photophysical properties of these CLgens in different states. It is found that molecular rigidity and proper conformation both play pivotal roles in improving the 1st TSI, enhancing the TSI linker and constructing 2nd TSI. Experimental and calculation results prove that the hierarchical TSIs and CL have been successfully regulated in these multiaryl-substituted alkanes (MAAs). This work not only provides a feasible strategy to achieve controllable manipulation of TSI and CL but also paves the way to the in-depth mechanistic understanding of CL.

Coherent and dissipative couplings are discovered in hybrid systems, which are frequently shown as the level repulsion and level attraction between the coupled modes, respectively. The coherent coupling can come from the direct dipole–dipole interaction or resonance‐mediated virtual photon exchange. The dissipative coupling originates from the bath‐induced cooperative damping effect. The interplay between these two couplings gives rise to complex coupling, contributing to novel phenomena and applications. In this work, it is studied how coherent and complex couplings can be readily realized and manipulated in a three‐mode cavity magnonic system. The three‐mode system consists of a two‐port cavity, a yttrium iron garnet (YIG) sphere (magnon mode), and a split‐ring resonator (auxiliary mode). A tunable split‐ring resonator mediates the coupling between the cavity mode and magnon mode. The coupling effect is theoretically analyzed by solving the steady‐state equation combined with numerical simulation. By adjusting several system parameters, the coherent and complex couplings mediated by the auxiliary mode are revealed. The study paves the way toward exploiting resonance‐ and dissipation‐induced couplings in hybrid systems.

For solid-state spin systems, the collective spin motion in a single crystal embodies multiple magnetostatic modes. Recently, it was found that the cross-Kerr interaction between the higher-order magnetostatic mode and the Kittel mode introduces a new operable degree of freedom. In this work we propose a scheme to entangle two magnon modes via the cross-Kerr nonlinearity when the bias field is inhomogeneous and the system is driven. Quantum entanglement persists at the steady state, as demonstrated by numerical results using experimentally feasible parameters. Furthermore, we also demonstrate that entangled states can survive better in the system where self-Kerr and cross-Kerr nonlinearities coexist. Our work provides insights and guidance for designing experiments to observe entanglement between different degrees of freedom within a single ferrimagnetic crystal. Additionally, it may stimulate potential applications in quantum information processing using spintronic devices.

The cooperation of coherent and dissipative coupling produces nonreciprocity in cavity magnonic devices, in which the isolation ratio can theoretically be infinite at a matching condition (zero-damping condition). In this article, we report the design of such a prototype, where a yttrium–iron–garnet sphere is strongly coupled to a planar microwave cavity resonator. Three different microwave isolator design schemes have been constructed according to the latest developed theory, resulting in considerable isolation, design flexibility, and device size reduction. Fabricated devices achieved the isolation of 65.8, 40.5, and 31.0 dB and the corresponding insertion loss of 23.6, 0.7, and 0.7 dB, respectively. These devices promise to be useful in microwave range applications that demand miniature, low cost, and narrowband. Furthermore, our magnonic device may open a promising way for signal processing through the manipulation of coherent and dissipative coupling.

We experimentally demonstrate the strong coupling between the ferromagnetic magnons in an yttrium-iron-garnet (YIG) sphere and the drive-field-induced dressed states of a superconducting qubit, which gives rise to the double dressing of the superconducting qubit. The YIG sphere and the superconducting qubit are embedded in a microwave cavity, and are coupled to the magnetic and electrical fields of the cavity \begin{document}$\mathrm{TE}_{102}$\end{document} mode, respectively. The effective coupling between them is mediated by the virtual cavity photons of cavity \begin{document}$\mathrm{TE}_{102}$\end{document} mode. Our experimental results indicate that as the power for driving the qubit increases, an additional split of the qubit-magnon polariton occurs. These supplemental splittings indicate a double-dressed state. We theoretically analyze the experimental results by using a particle-hole symmetric model. The theoretical results fit the experimental observations well in a broad range of drive-field power parameters, revealing that the driven qubit-magnon hybrid quantum system can be used to emulate a particle-hole symmetric pair coupled to a bosonic mode. Our hybrid quantum system holds great promise for quantum simulations of composite quasiparticles consisting of fermions and bosons.

Squeezed light finds many important applications in quantum information science and quantum metrology,and has been produced in a variety of physical systems involving optical non-linear processes.Here,we show how a non-linear magnetostrictive interaction in a ferrimagnet in cavity magnomechanics can be used to reduce quantum noise of the electromagnetic field.We show optimal parameter regimes where a substantial and stationary squeezing of the microwave output field can be achieved.Realization of the scheme is within reach of current technology in cavity electromagnonics and magnomechanics.Our work provides a new and practicable approach for producing squeezed vacuum states of electromagnetic fields,and may find promising applications in quantum information processing and quantum metrology.