Yttrium Iron Garnet Sphere Research Articles

Generation and transfer of squeezed states in a cavity magnomechanical system by two-tone microwave fields.

We propose a scheme to generate squeezed states of magnon and phonon modes and verify squeezing transfer between different modes of distinct frequencies in a cavity magnomechanical system which is composed of a microwave cavity and a yttrium iron garnet sphere. We present that by activating the magnetostrictive force in the ferrimagnet, realized by driving the magnon mode with red-detuned and blue-detuned microwave fields, the driven magnon mode can be prepared in a squeezed state. Moreover, the squeezing can be transferred to the cavity mode via the cavity-magnon beamsplitter interaction with strong magnomechanical coupling. We show that under the weak coupling regime, large mechanical squeezing of phonon mode can be achieved, which verifies that our scheme can find the existence of quantum effects at macroscopic scales. Furthermore, distinct parameter regimes for obtaining large squeezing of the magnons and phonons are given, which is the principal feature of our scheme. The considered scheme can be extended to hybrid optical systems, and can facilitate the advancement for realization of strong mechanical squeezing in cavity magnomechanical systems.

Direct excitation of the magnetisation in photon-magnon hybrid systems with an infrared laser pulse

We present experimental results concerning the direct excitation of the magnetisation in a photon-magnon hybrid system composed of a microwave cavity and an embedded yttrium iron garnet (YIG) sphere. An 11 ps ultrafast pulsed laser, with wavelength of 1064 nm outside the YIG transparence window, directly excite the magnon modes. We measure the energy deposited in the Kittel mode of magnetisation by exploiting its coupling to the TE102 mode of the rectangular microwave cavity in the strong coupling regime. Energy collection is performed by a standard rf detection chain reading an antenna matched to the cavity resonance. This technique can prove to be essential in the study of the dynamics of cavity magnon-polaritons, finding application in dark matter axion searches and future magnon based quantum information studies.

Active control of electron cyclotron emission radiometer channel frequencies for improved electron temperature measurements.

As advanced scenarios are developed for tokamak operations, the demand for flexibility of the electron cyclotron emission (ECE) channels' locations has increased. The tunable feature of yttrium iron garnet (YIG) filters provides this spatial flexibility. Here, we present a method of performing ECE measurements on fixed flux surfaces instead of fixed frequencies. This is achieved by adjusting YIG filters utilized in the intermediate frequency section to frequencies associated with flux surfaces in regions of interest during the discharge. The key components are the application of tunable YIG filters and a control program that calculates the filter settings using flux information from real-time reconstruction equilibria (EFIT). This fast procedure facilitates Te measurements in regions of interest to investigate plasma dynamic behaviors.

Fast modulating electron cyclotron emission (FMECE) diagnostic for tokamaks.

Utilizing variable-frequency channels, e.g., yttrium iron garnet (YIG) bandpass filters, in the intermediate frequency (IF) section of an electron cyclotron emission (ECE) radiometer facilitates flexibility in the volume viewed by the ECE channels as well as high resolution electron temperature and temperature fluctuation measurements in tokamaks. Fast modulating electron cyclotron emission (FMECE), a stand-alone IF section with eight channels, is a novel application of YIG filters for real-time electron temperature gradient and gradient scale length measurements. Key to FMECE is a simultaneous input/output data acquisition unit, as well as a modified type of YIG filters, which is capable of fast switching of their center (set) frequencies with a frequency slew rate of 600 µs/GHz. A new FMECE has been implemented and tested on the DIII-D tokamak, demonstrating its capability in real-time gradient measurements. The data presented here shows that FMECE can identify flattening in the electron temperature profile; the latter can be used as a sensor for real time monitoring and control of plasma instabilities. Implementation and application are planned for the EAST tokamak.

Einstein-Podolsky-Rosen entanglement and asymmetric steering between distant macroscopic mechanical and magnonic systems

We propose a deterministic scheme for establishing hybrid Einstein-Podolsky-Rosen (EPR) entanglement channel between a macroscopic mechanical oscillator and a magnon mode in a distant yttrium-iron-garnet (YIG) sphere across about ten gigahertz of frequency difference. The system consists of a driven electromechanical cavity which is unidirectionally coupled to a distant electromagnonical cavity inside which a YIG sphere is placed. We find that far beyond the sideband-resolved regime in the electromechanical subsystem, stationary phonon-magnon EPR entanglement can be achieved. This is realized by utilizing the output field of the electromechanical cavity being an intermediary which distributes the electromechanical entanglement to the magnons, thus establishing a remote phonon-magnon entanglement. The EPR entanglement is strong enough such that phonon-magnon quantum steering can be attainable in an asymmetric manner. This long-distance macroscopic hybrid EPR entanglement and steering enable potential applications not only in fundamental tests of quantum mechanics at the macro scale, but also in quantum networking and one-sided device-independent quantum cryptography based on magnonics and electromechanics.

Nonlocal magnon entanglement generation in coupled hybrid cavity systems.

We investigate dynamical generation of macroscopic nonlocal entanglements between two remote massive magnon-superconducting-circuit hybrid systems. Two fiber-coupled microwave cavities are employed to serve as an interaction channel connecting two sets of macroscopic hybrid units, each containing a magnon (hosted by an yttrium-iron-garnet sphere) and a superconducting-circuit qubit. Surprisingly, it is found that stronger coupling does not necessarily mean faster entanglement generation. The proposed hybrid system allows the existence of an optimal fiber coupling strength that requires the shortest amount of time to generate a systematic maximal entanglement. Our theoretical results are shown to be within the scope of specific parameters that can be achieved with current technology. The noise effects on the implementation of systems are also treated in a general environment, suggesting the robustness of entanglement generation. Our discrete-variable qubit-like entanglement theory of magnons may lead to direct applications in various quantum information tasks.

Investigation of the giant magneto-impedance effect of single crystalline YIG based on the ferromagnetic resonance effect

We investigated the giant magneto-impedance (GMI) effect on ferrimagnetic insulator yttrium iron garnet (YIG) films and spheres, and the ferromagnetic resonance effect played a vital role. The GMI results were derived from the high-frequency measurements of a microwave transmission line loaded with YIG films and spheres. Our findings showed that there were obvious distinctions in the impedance of the transmission line loaded with single crystalline YIG samples depending on the external magnetic field, which indicates the significant GMI effect. The maximum GMI ratio as high as 256% was achieved, corresponding to a magnetic response of 8.8%/Oe. This study reveals that single crystalline YIG films are promising candidates for using as probe element in chip-scale magnetic sensors.

Tripartite entanglement in a Laguerre–Gaussian rotational-cavity system with an yttrium iron garnet sphere

We propose a scheme that can realize the tripartite entanglement between the Laguerre–Gaussian (L–G) cavity mode, magnon mode, and phonon (rotating) mode in a hybrid rotating cavity optomechanical system with an yttrium iron garnet sphere inside the cavity. The excited magnon mode and the L–G cavity mode are related through the magnetic dipole interaction, and the L–G cavity mode can exchange orbital angular momentum (OAM) with the rotating mirror. In this way, the magnon mode and the rotating mirror are connected through the L–G cavity mode. Our results show that physical parameters such as OAM of the L–G cavity mode, detuning of the magnon mode, and effective detuning of the cavity mode play different roles in establishing entanglements.

Effect of dipolar interactions on cavity magnon polaritons

The strong photon-magnon coupling between an electromagnetic cavity and two yttrium iron garnet (YIG) spheres has been investigated in the context of a strong mutual dipolar interaction between the spheres. A decrease in the coupling strength between the YIG spheres and the electromagnetic cavity is observed, along with an increase of the total magnetic losses, as the distance between the spheres is decreased. A model of inhomogeneous broadening of the ferromagnetic resonance linewidth, partly mitigated by the dipolar narrowing effect, reproduces the reduction in the coupling strength observed experimentally. These findings have important implications for the understanding of strongly coupled photon-magnon system involving densely packed magnetic objects, such as ferromagnetic nanowires arrays, in which the total coupling strength with an electromagnetic cavity might become limited due to mutual dipolar interactions.

Resonances in large ferrimagnetic YIG samples – Electrodynamic analysis

Electrodynamic (ED) analysis of the TEn0p (TEθφr) modes in a shielded single-crystal-5-mm-diameter yttrium iron garnet (YIG) sphere has been performed and compared with the results of previous experiments. Measurements and ED analysis of the HE111± mode resonances in a polycrystalline Al-doped rod-shaped YIG sample have been performed for comparison. It has been shown that electromagnetic resonances in large shielded YIG spheres behave in a similar way as typical resonances occurring in dielectric resonators under conditions when the effective permeability is positive, and as so-called magnon resonances when the effective permeability is negative. Nevertheless, both types of resonances are solutions to the same transcendental equation. Computations reported herein suggest that the physical nature of resonance systems containing dispersive gyrotropic media can be described within a common framework of electromagnetic resonance systems with unequal stored magnetic and electric energies, which offers an alternative to the more widely used quantum and harmonic oscillator models.

Stationary Entanglement between Light and Microwave via Ferromagnetic Magnons

AbstractIt is shown how to generate stationary entanglement between light and microwave in a hybrid opto‐electro‐magnonical system which mainly consists of a microwave cavity, a yttrium iron garnet (YIG) sphere, and a nanofiber. The optical modes in nanofiber can evanescently be coupled to whispering gallery modes, that are able to interact with magnon mode via spin–orbit interaction, in YIG sphere, while the microwave cavity photons and magnons are coupled through magnetic dipole interaction simultaneously. Under reasonable parameter regimes, pretty amount of entanglement can be generated, and it also shows persistence against temperature. The present work is expected to provide a new perspective for building more advanced and comprehensive quantum networks along with magnons for fast‐developing quantum technologies and for studying the macroscopic quantum phenomena.

Tunable multiwindow magnomechanically induced transparency, Fano resonances, and slow-to-fast light conversion

We investigate the absorption and transmission properties of a weak probe field under the influence of a strong control field in a cavity magnomechanical system. The system consists of two ferromagnetic-material yttrium iron garnet (YIG) spheres coupled to a single cavity mode. In addition to two magnon-induced transparencies (MITs) that arise due to magnon-photon interactions, we observe a magnomechanically induced transparency (MMIT) due to the presence of nonlinear magnon-phonon interaction. We discuss the emergence of Fano resonances and explain the splitting of a single Fano profile to double and triple Fano profiles due to additional couplings in the proposed system. Moreover, by considering a two-YIG system, the group delay of the probe field can be enhanced by one order of magnitude as compared with a single-YIG magnomechanical system. Furthermore, we show that the group delay depends on the tunability of the coupling strength of the first YIG with respect to the coupling frequency of of the second YIG, and vice versa. This helps to achieve larger group delays for weak magnon-photon coupling strengths.

Optomagnonic Devices: Nonreciprocal Transmission and Nonreciprocal Entanglement in a Spinning Microwave Magnomechanical System (Ann. Phys. 9/2020)

A nonreciprocal optomagnonic device that has dual properties of classical and quantum nonreciprocity is proposed by Hong-Yu Liu, Rong-Can Yang, and co-workers in article number 2000196. The system consists of a magnon mode and a mechanical mode of the YIG sphere and a spinning microwave oscillator. Due to the Fizeau light-dragging effect, the effective cavity frequency can be shifted by the direction of the input light, leading to a nonreciprocal magnon–phonon entangled state.

Coherent multimode conversion from microwave to optical wave via a magnon-cavity hybrid system

Coherent conversion from microwave to optical wave opens new research avenues towards a long distance quantum network covering quantum communication, computing, and sensing out of the laboratory. Especially a multimode enabled system is essential for practical applications. Here we experimentally demonstrate coherent multimode conversion from the microwave to optical wave via collective spin excitation in a single crystal yttrium iron garnet (YIG, ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$) which is strongly coupled to a microwave cavity mode in a three-dimensional rectangular cavity. Expanding a collective spin excitation mode of our magnon-cavity hybrid system from Kittel to multimagnetostatic modes, we verify that the size of the YIG sphere predominantly plays a crucial role for the microwave-to-optical multimode conversion efficiency at resonant conditions. We also find that the coupling strength between multimagnetostatic modes and a cavity mode is manipulated by the position of a YIG inside the cavity. It is expected to be valuable for designing a magnon-hybrid system that can be used for coherent conversion between microwave and optical photons.

Nonreciprocal Transmission and Nonreciprocal Entanglement in a Spinning Microwave Magnomechanical System

AbstractThis study presents nonreciprocal transmission and nonreciprocal magnon–phonon entanglement in a spinning microwave magnomechanical system. This system consists of microwave photons, magnon modes, and phonons. These are created by the vibrational mode of a yttrium iron garnet sphere. This investigation reveals that nonreciprocity is caused by the light that is circulating in a resonator that is experiencing a Fizeau shift. This leads to a difference in the effective detuning frequency of the photon for forwarding and backward drives. A super‐strong transmission isolation rate (>100 dB) and a strong entanglement isolation rate (≈50 dB) are obtained by applying the experimental parameters. This scheme opens a new route for exploiting a variety of nonreciprocal effects, and it provides the theoretical basis for the design and realization of magnetically controllable isolators and diodes.

Sub-Poissonian statistics and squeezing of magnons due to the Kerr effect in a hybrid coupled cavity–magnon system

We investigate theoretically the quantum dynamics and statistics of magnons in a cavity–magnon system, where the magnons in a single yttrium iron garnet (YIG) sphere are coupled to microwave cavity photons. Under the rotating wave approximation, the Hamiltonian of the system is solved analytically. By using the coherent magnon state representation, we show that the magnon Kerr nonlinearity, which originates in the magnetocrystalline anisotropy in the YIG sample, could yield a periodic sub-Poissonian distribution and quadrature squeezing effects in the magnons. The generation and manipulation of these nonclassical quantum statistical properties of the magnons can be controlled by scaling the size of the YIG sample.

Sharply vanishing destructive interference induced by magnon Kerr effect in cavity magnon polaritons

Motivated by the recently discovered nonlinear dynamics of cavity–magnon polaritons (CMPs), bistable CMP behavior is investigated theoretically in the case of two yttrium iron garnet (YIG) spheres (YIG1 and YIG2) in a microwave cavity, which is induced by the magnon Kerr effect of YIG1 originating from the magnetocrystalline anisotropy. The bistability appears in the form of sharp CMP frequency switching. More importantly, when the driving field acts on YIG1 and drives the magnon dark mode, the nonlinear Kerr effect at high excitation plays an important role in creating frequency detuning between the two YIG spheres. This results in sharply vanishing destructive interference between two YIG spheres and simultaneously makes the invisible magnon dark mode visible. However, when the driving field acts on the cavity, the magnon dark mode remains dark and there is no bistability in the CMPs when the driving frequency is tuned to the magnon dark mode, this being because the excitation energy cannot be transferred from cavity to magnon. The present research provides a promising approach for information storage and processing in multimode systems under high excitation.

Manipulation of bistability through the coupling strength in cavity magnon polaritons

Benefiting from the latest experiment of non-linearity in cavity magnon polaritons due to the magnetocrystalline anisotropy in the yttrium iron garnet (YIG) crystal, we theoretically propose a cavity magnonics model that can be used to study the bistable behaviors by changing the coupling strength, which presents the rich and interesting phenomena. In the case of resonance, the critical driving powers of the upper and lower polariton modes have the smaller values for the larger coupling strength but the larger values for the smaller coupling strength. In addition, the upper and lower polariton modes show the repulsive and attractive features, respectively, when the derivative of the coupling strength with respect to the position of the YIG sphere changes from positive to negative. Especially, the bistability of the lower polariton mode disappears when the driving power is strong enough. Our research broadens the means of manipulation of non-linearity in cavity magnon system, which provides a promising application for cavity spintronics and information processing.

Manipulation of the zero-damping conditions and unidirectional invisibility in cavity magnonics

In this paper, we report a cavity magnonic system consisting of a split-ring resonator coupled with a yttrium iron garnet sphere, in which both coherent and dissipative coupling strengths can be tuned continuously, thereby making the zero damping conditions (ZDCs) controllable in a frequency range up to 100 MHz. Unidirectional invisibility has been observed under the ZDCs, with the microwaves freely transmitted in the forward direction (−2.9 dB) but almost completely blocked in the backward direction (−83 dB). The effective isolation ratio reaches up to 80 dB, which has surpassed the ideal isolation ratio limited by the state-of-the-art technique, and its direction is reversible by the orientation of the external static magnetic field. As an unconventional nonreciprocal device with flexibility and sensitivity, our magnonic device may open a promising way for robust coherent and quantum information processing.

Axion Search with a Quantum-Limited Ferromagnetic Haloscope.

A ferromagnetic axion haloscope searches for dark matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier. The hybrid system consists of ten 2.1mm diameter yttrium iron garnet spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin magnetometer ever realized. The minimum detectable field is 5.5×10^{-19} T with 9h integration time, corresponding to a limit on the axion-electron coupling constant g_{aee}≤1.7×10^{-11} at 95%C.L. The scientific run of our haloscope resulted in the best limit on dark matter axions to electron coupling constant in a frequency span of about 120MHz, corresponding to the axion-mass range 42.4-43.1 μeV. This is also the first apparatus to perform a wide axion-mass scanning by only changing the static magnetic field.