Magnon Modes Research Articles

Quantum effect in a hybrid bose-einstein condensate opto-magnomechanical system

Abstract We present a hybrid opto-magno-mechanical cavity system consisting of an optical cavity that creates an opto-mechanical cavity with a fixed mirror, a magnon mode in a ferrimagnetic crystal linked to the movable mirror and an intracavity Bose–Einstein condensate. The mechanical displacement is coupled to the magnon by the magnetostriction force and to the optical cavity by the radiation pressure, and the latter is also weakly coupled to a Bose–Einstein condensate. We provide a strategy to measure and quantify entanglement using logarithmic negativity. In addition, we study the quantum or EPR steering in order to present the stationary quantum steering. We consider that all composite modes in our model are given in a Gaussian state described by a covariance matrix. In these studies, we focus on the interaction between the Bose–Einstein condensate and the magnonic modes in a ferrimagnetic crystal. It is important to note that we use experimentally controllable realizable parameters to observe the interaction of modes at temperatures in the microkelvin range.

Spin switching in Sm0.7Er0.3FeO3 triggered by terahertz magnetic-field pulses.

Driving spin systems to states far from equilibrium is indispensable in investigations of functional nonlinearities of antiferromagnets for spintronics. So far, it has been shown that electric-field pulses in the spectral region from the visible to the terahertz range can be used to induce ultrafast switching between different spin states. Here we demonstrate that a multicycle terahertz magnetic-field pulse can be used to induce non-thermal spin switching in antiferromagnets. When a strong pulse is applied to Sm0.7Er0.3FeO3, the magnetic order parameter is first driven away from the barrier between the two potential minima of this antiferromagnet and then, in the subsequent inertial motion towards the opposite direction, it crosses the barrier. Our analysis reveals that the initial motion is driven by a dynamical modification of the magnetic potential, and this modification is enhanced through coupling between the two magnon modes.

Enhanced sensing of anharmonicities in a gain-based anti-PT symmetric system

Abstract We study the enhanced sensing of weak anharmonicities in a gain-based cavity-magnon-waveguide coupled system. By dissipatively coupling the two subsystems through a mediating waveguide, the Hamiltonian of the system is tailored to be anti-parity-time symmetric. Unique to the gain condition, the eigenvalues exhibit two singularities with linewidth suppression, distinguishing it from gain-free systems. Under the gain condition, a counter-intuitive bistable signature emerges even at low drive powers. As the effective gain approaches a certain value, this bistability yields a significantly enhanced spin-current response of the magnon mode. Consequently, the sensitivity, quantified by an enhancement factor, is enhanced remarkably compared to the linewidth suppression scenario. Moreover, the high enhancement factor can be sustained over a broad gain-bandwidth and also retains large even when the coherent coupling becomes considerably strong. Based on the integrated cavity-magnon-waveguide systems, the scheme can be used for sensing different physical quantities related to the Kerr-type nonlinearity and has potential applications in high-precision measuring microwave-signal nonlinearities.

Modulating nonreciprocal transmission in levitated magnomechanical systems

In this paper, we propose a model of a dual cavity magnomechanical system with two levitated yttrium iron garnet spheres to investigate nonreciprocal transmission of a microwave field. We use an external Coulomb force to bias the steady-state position of the sphere levitated in each microwave cavity, thereby establishing an independent and controllable effective couplings between the cavity modes and the magnon modes. This can break the symmetry of the system and serve as the basis for nonreciprocal transmission in this system. We demonstrated how to achieve the system nonreciprocity with an extremely high isolation ratio and flexible controllability by appropriately selecting the suspended positions of the levitated spheres, which are related to the external bias forces. We also analyze in detail the influence of the cavity detunings and the driving power on the bias-force-induced nonreciprocity. Our study provides an effective approach to manipulating flexibly nonreciprocal transmission of a microwave field and may have potential implications for the development of future nonreciprocal transmission devices.

Terahertz Crystal-Field Transitions and Quasi Ferromagnetic Magnon Excitations in a Noncollinear Magnet for Hybrid Spin-Wave Computation.

The complexity of interactions between the crystal-field and unusual noncollinear spin arrangement in nontrivial magnets demands novel tools to unravel the mystery underneath. In this work, we study such interaction dynamics of crystal-field excitations (CFE) and low-energy magnetic excitations in orthochromite TmCrO3 with controls of temperature and magnetic field using high-resolution magneto-terahertz (THz) time-domain spectroscopy. The THz energy spectrum spanning 0.5-10 meV possesses a low-frequency spin-excitation (magnon) mode and a multitude of CFE modes at 10 K, all of which uniquely embody a range of phenomena. For the magnon mode, a temperature dependence of peak frequency is induced by magnetic interactions between Tm and Cr subsystems. While a change from blue to red shift of peak frequency of this mode marks the magnetization reversal transition, the spin-reorientation temperature and change of magnetic anisotropy are depicted by different features of field and temperature dependent peak frequency dynamics. The modes corresponding to CFE are robust and laden with a multitude of submodes, which are attributes of nontrivial interactions across different transitions. These modes are suppressed only upon substitution of Tb3+ at the Tm3+ site, which suggests a dominant role of single-ion anisotropy in controlling entire THz excitation spectra. Overall, this remarkable range of phenomena seen through the unique lens of all-optical THz tools provides deeper insights into the origin of magnetic phases in systems with complex interactions between rare-earth and transition metal ions and provides a multitude of novel combinations of closely spaced modes for emerging hybrid spin-wave computation.

Magnon squeezing via reservoir-engineered optomagnomechanics

We show how to prepare magnonic squeezed states in an optomagnomechanical system in which magnetostriction induced mechanical displacement couples to an optical cavity via radiation pressure. We discuss two scenarios depending on whether the magnomechanical coupling is linear or dispersive. We show that in both cases the strong mechanical squeezing obtained via two-tone driving of the optical cavity can be efficiently transferred to the magnon mode. In the linear coupling case, stationary magnon squeezing is achieved, while in the dispersive coupling case, a transient magnonic squeezed state is prepared in a two-step protocol. The proposed magnonic squeezed states find promising applications in quantum information processing and quantum sensing using magnons.

Spin dynamics and possible topological magnons in the nonstoichiometric pyrochlore iridate Tb2Ir2O7 studied by RIXS

We report on a resonant inelastic x-ray scattering study on a single crystal of a nonstoichiometric pyrochlore iridate Tb2+xIr2−xO7−y (x≃0.25) that magnetically orders at TN≃50 K. We observe a propagating gapped magnon mode at low energy and model it using a Hamiltonian consisting of a Heisenberg exchange [J=16.2(9)meV] and Dzyaloshinskii-Moriya interactions [D=5.2(3)meV], which shows the robustness of interactions despite Tb stuffing at the Ir site. Strikingly, the ratio D/J=0.32(3) supports possible nontrivial topological magnon band crossing. This material may thus host coexisting fermionic and bosonic topology, with potential for manipulating electronic and magnonic topological bands thanks to the d−f interaction. Published by the American Physical Society 2024

Generation of quantum entanglement and Einstein–Podolsky–Rosen steering in a hybrid qubit-cavity optomagnonic system

We propose a scheme to generate quantum entanglement and Einstein–Podolsky–Rosen (EPR) steering in a hybrid qubit-cavity optomagnonic system. This hybrid system consists of a microwave cavity, a yttrium-iron-garnet (YIG) sphere, and a superconducting qubit. Due to the existence of the effective parametric (beamsplitter) coupling between the optical mode and the magnon mode (superconducting qubit), the quantum entanglement and EPR steering between the magnon and qubit modes can be achieved. It is found that bipartite entanglement and one-way quantum steering are limited to a narrow range of parameters, while two-way quantum steering appears in a wide range of parameters. Furthermore, we demonstrate that the entanglement between the magnon and the collective dressed modes, as well as the conversion of one-way quantum steering, can also be achieved. Our scheme may provide a feasible approach to exploring quantum information processing.

Magnetic excitation in the hyperkagome antiferromagnet Mn3RhSi

In a paramagnetic state of a hyperkagome lattice antiferromagnet Mn3RhSi, magnetic diffuse scattering by magnetic short-range order is observed over a wide temperature range of approximately 500 K above the Néel temperature of 190 K. We have studied the magnetic excitation with a single crystal in a wide energy range from 0.3 to 140 meV by inelastic neutron scattering, where the prominent inelastic neutron-scattering signal is observed at Q=(2,0,0). The inelastic scattering intensity integrated for two of twelve magnon modes leads to a localized magnetic moment of about 5 μB per Mn site, although the long-range ordered magnetic moment is only 2.61 μB at 4 K. The result suggests that a large part of the magnetic moment does not order in Mn3RhSi, possibly due to the geometrical spin frustration of the hyperkagome lattice. Published by the American Physical Society 2024

Microwave‐to‐Optics Conversion Using Magnetostatic Modes and a Tunable Optical Cavity

AbstractQuantum 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 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.

Quantum Correlation Enhanced with Quantum Coherent Feedback Control in a Cavity‐magnon Hybrid System

AbstractA scheme is proposed to enhance quantum correlation, including entanglement and steering, for two magnon modes in a cavity‐magnon hybrid system through coherent quantum feedback. The hybrid system consists of a microwave cavity and two YIG spheres, which incorporates a nonlinear flux‐driven Josephson parametric amplifier in order for the generation of two photons within the cavity simultaneously. A quantum coherent feedback loop is used for the reduction of effective dissipation. By modulating feedback parameters, optimal bipartite and tripartite entanglement, as well as quantum steering are derived. Importantly, compared with the same setup without coherent feedback, the proposed scheme significantly improves quantum correlation. Furthermore, by optimizing the feedback reflectivity and the ratio of cavity‐magnon coupling strength, the enhancement of asymmetric steering can be controlled. Notably, incorporating the feedback loop effectively increase its robustness against thermal noise, thus the scheme offer better prospect for experimental development. This study paves the way for advancements in quantum information processing and quantum entanglement within cavity‐magnonics.

Engineering and control of the entanglement for four Magnon modes inside two microwave cavities

Engineering and control of the entanglement for four Magnon modes inside two microwave cavities

Manipulating the nonreciprocal microwave transmission by using a pump-induced magnon mode

We realize the electromagnetic regulation of nonreciprocal microwave transmission by introducing a pump-induced magnon mode (PIM) into a cavity magnonic device with dissipative photon–magnon coupling. As a peculiar spin wave, the PIM's dynamic properties, including its spin number and resonant frequency, can be easily tuned by the microwave pump. Hence, it facilitates the precise control of the coupling process between the PIM and the cavity magnonic device by regulating the pump signal. Along with these manipulations, the nonreciprocal microwave transmission produced by the dissipative photon–magnon coupling is regulated without reconfiguring the system. In the experiment, we achieve a pump-controlled nonreciprocal bandwidth of 16 MHz and a pump-tunable isolation range of up to 40 dB. Our work demonstrates the control of a microwave with another microwave. It has a great potential in the design of fast microwave switches and programmable isolators for information processing.

Tailoring magnon modes by extending square, kagome, and trigonal spin ice lattices vertically via interlayer coupling of trilayer nanomagnets

In this work high-frequency magnetization dynamics and statics of artificial spin-ice lattices with different geometric nanostructure array configurations are studied where the individual nanostructures are composed of ferromagnetic/non-magnetic/ferromagnetic trilayers with different non-magnetic thicknesses. These thickness variations enable additional control over the magnetic interactions within the spin-ice lattice that directly impacts the resulting magnetization dynamics and the associated magnonic modes. Specifically the geometric arrangements studied are square, kagome and trigonal spin ice configurations, where the individual lithographically patterned nanomagnets (NMs) are trilayers, made up of two magnetic layers of Ni81Fe19 of 30 nm and 70 nm thickness respectively, separated by a non-magnetic copper layer of either 2 nm or 40 nm. We show that coupling via the magnetostatic interactions between the ferromagnetic layers of the NMs within square, kagome and trigonal spin-ice lattices offers fine-control over magnetization states and magnetic resonant modes. In particular, the kagome and trigonal lattices allow tuning of an additional mode and the spacing between multiple resonance modes, increasing functionality beyond square lattices. These results demonstrate the ability to move beyond quasi-2D single magnetic layer nanomagnetics via control of the vertical interlayer interactions in spin ice arrays. This additional control enables multi-mode magnonic programmability of the resonance spectra, which has potential for magnetic metamaterials for microwave or information processing applications.

Voltage control of multiferroic magnon torque for reconfigurable logic-in-memory

Magnons, bosonic quasiparticles carrying angular momentum, can flow through insulators for information transmission with minimal power dissipation. However, it remains challenging to develop a magnon-based logic due to the lack of efficient electrical manipulation of magnon transport. Here we show the electric excitation and control of multiferroic magnon modes in a spin-source/multiferroic/ferromagnet structure. We demonstrate that the ferroelectric polarization can electrically modulate the magnon-mediated spin-orbit torque by controlling the non-collinear antiferromagnetic structure in multiferroic bismuth ferrite thin films with coupled antiferromagnetic and ferroelectric orders. In this multiferroic magnon torque device, magnon information is encoded to ferromagnetic bits by the magnon-mediated spin torque. By manipulating the two coupled non-volatile state variables—ferroelectric polarization and magnetization—we further present reconfigurable logic operations in a single device. Our findings highlight the potential of multiferroics for controlling magnon information transport and offer a pathway towards room-temperature voltage-controlled, low-power, scalable magnonics for in-memory computing.

Magnon Excitation Modes in Ferromagnetic and Antiferromagnetic Systems

Magnons, recognized as the quanta of spin waves, offer a pathway for transmitting information without the need for electron motion, thus emerging as a leading candidate for the next generation of low-power electronics. Firstly, this study gives an overview by examining magnon modes possessing infinite wavelengths or zero wave numbers (known as ferromagnetic resonance) in classical ferromagnetic, antiferromagnetic, and synthetic antiferromagnetic systems. It delves into the dynamics of magnetization, particularly focusing on magnetic moments precession and the corresponding dispersion relationships under two distinct acoustic and optic eigenmodes. Furthermore, it elaborates on a novel hybrid quantum system termed magnon-magnon coupling. The study elucidates the mechanism behind the robust coupling between acoustic and optic magnon modes. Finally, we briefly discuss the current challenges and future research directions in this field.

Entanglement enhancement of two different magnon modes via nonlinear effect in cavity magnomechanics

Entanglement enhancement of two different magnon modes via nonlinear effect in cavity magnomechanics

Confined magnon dispersion in ferromagnetic and antiferromagnetic thin films in a second quantization approach: The case of Fe and NiO

We present a methodology based on the calculation of the inelastic scattering from magnons via the spin-scattering function in confined geometries such as thin films using a second quantization formalism, for both ferromagnetic and antiferromagnetic materials. The case studies are chosen with an aim to demonstrate the effects of film thickness and crystal orientation on magnon modes, using bcc Fe(100) and NiO with (100) and (111) crystallographic orientations as prototypical systems. Due to the quantization of the quasimomentum, we observe a granularity in the inelastic spectra in the reciprocal space path reflecting the orientation of the thin film. This approach also allows for the capture of softer modes that appear due to the partial interaction of magnetic moments close to the surface in a thin film geometry, in addition to bulk modes. The softer modes are also affected by crystallographic orientation, as illustrated by the different surface-related peaks of the NiO magnon density of states at approximately ∼65meV for (100) and ∼42meV for a (111)-oriented film. Additionally, we explore the role of anisotropy, revealing that anisotropy increases the overall hardness of the magnon modes. The introduction of a surface anisotropy produces a shift of the surface-related magnon DOS peak to higher energies with increased surface anisotropy, and in some cases leads to a surface-confined mode. Published by the American Physical Society 2024

Entropy production rate and correlations in a cavity magnomechanical system

We present the irreversibility generated by a stationary cavity magnomechanical system composed of a yttrium iron garnet (YIG) sphere with a diameter of a few hundred micrometers inside a microwave cavity. In this system, the magnons, i.e., collective spin excitations in the sphere, are coupled to the cavity photon mode via magnetic dipole interaction and to the phonon mode via magnetostrictive force (optomechanical-like). We employ the quantum phase-space formulation of the entropy change to evaluate the steady-state entropy production rate and associated quantum correlation in the system. We find that the behavior of the entropy flow between the cavity photon mode and the phonon mode is determined by the magnon-photon coupling and the cavity photon dissipation rate. Interestingly, the entropy production rate can increase/decrease depending on the strength of the magnon-photon coupling and the detuning parameters. We further show that the amount of correlations between the magnon and phonon modes is linked to the irreversibility generated in the system for small magnon-photon coupling. Our results demonstrate the possibility of exploring irreversibility in driven magnon-based hybrid quantum systems and open a promising route for quantum thermal applications. Published by the American Physical Society 2024

Dipole–dipole-interaction-induced entanglement between two-dimensional ferromagnets

We investigate the viability of dipole–dipole interaction as a means of entangling two distant ferromagnets. To this end, we make use of the Bogoliubov transformation as a symplectic transformation. We show that the coupling of the uniform magnon modes can be expressed using four squeezing parameters, which we interpret in terms of hybridization, one-mode, and two-mode squeezing. We utilize the expansion in terms of the squeezing parameters to obtain an analytic formula for the entanglement in the magnon ground state using the logarithmic negativity as entanglement measure. Our investigation predicts that for infinitely large two-dimensional ferromagnets, the dipole–dipole interaction does not lead to significant long-range entanglement. However, in the case of finite ferromagnets, finite entanglement can be expected.