Yttrium Iron Garnet Sphere Research Articles

Coherent Coupling of Two Remote Magnonic Resonators Mediated by Superconducting Circuits.

We demonstrate microwave-mediated distant magnon-magnon coupling on a superconducting circuit platform, incorporating chip-mounted single-crystal Y_{3}Fe_{5}O_{12} (YIG) spheres. Coherent level repulsion and dissipative level attraction between the magnon modes of the two YIG spheres are demonstrated. The former is mediated by cavity photons of a superconducting resonator, and the latter is mediated by propagating photons of a coplanar waveguide. Our results open new avenues toward exploring integrated hybrid magnonic networks for coherent information processing on a quantum-compatible superconducting platform.

Auxiliary Mode Mediated Coherent and Complex Couplings in a Cavity Magnonic System

AbstractCoherent 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.

Coherent coupling in a driven qubit-magnon hybrid quantum system

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 <inline-formula><tex-math id="M2">\begin{document}$\mathrm{TE}_{102}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220260_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220260_M2.png"/></alternatives></inline-formula> mode, respectively. The effective coupling between them is mediated by the virtual cavity photons of cavity <inline-formula><tex-math id="M3">\begin{document}$\mathrm{TE}_{102}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220260_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20220260_M3.png"/></alternatives></inline-formula> 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.

Nonspherical optomagnonic resonators for enhanced magnon-mediated optical transitions

We study magnon-mediated optical transitions in micrometer-sized axially symmetric yttrium iron garnet (YIG) particles, which act as optomagnonic cavities, by means of electromagnetic calculations, treating the magneto-optical coupling to first order in perturbation theory, in the framework of a fully dynamic approach. Such particles with engineered shape anisotropy exhibit high-quality-factor Mie resonances in the infrared part of the spectrum, with a separation of few gigahertz, which matches the typical frequencies of magnons. This allows for optical transitions mediated by spin waves, while the micrometer volume favors stronger overlap between the optical modes and the precessing magnetization. Our results predict that photon-magnon coupling strengths of tens of kilohertz could be realized with cylindrical or spheroidal particles, since mainly the reduced volume, but also shape anisotropy, can lead to strong, up to four orders of magnitude, enhancement of the coupling strengths compared to submillimeter YIG spheres.

Nonreciprocal magnon laser.

A nonreciprocal magnon laser is proposed in a compound cavity optomagnonical system consisting of an yttrium iron garnet sphere coupled to a spinning resonator. On the basis of the magnon-induced Brillouin scattering process making it possible to achieve a magnon lasing action, the Fizeau light-dragging effect caused by the spinning of the resonator further results in significant modifications in the magnon gain and the threshold power of magnon lasing for different driving directions, and then a nonreciprocal magnon laser is realized. Especially, this nonreciprocal magnon laser is highly tunable by the spinning speed and the driving direction. Our work provides an experimentally feasible pathway for manipulating spin-wave excitations and may find intriguing phenomena at the crossroad between spintronics of the magnet and nonreciprocal optics.

Entangling magnon and superconducting qubit by using a two-mode squeezed-vacuum microwave field

We propose a scheme to generate entanglement between magnon and superconducting qubit. The macroscopic yttrium–iron–garnet sphere and superconducting qubit are installed in two spatially separated cavities, which are directly driven by a two-mode squeezed-vacuum microwave field. The magnon and cavity 1 are coupled via magnetic dipole interaction and the superconducting qubit and cavity 2 are coupled via electric dipole interaction. We theoretically demonstrate that the magnon–qubit steady-state entanglement can be created by transferring quantum correlations of the two-mode squeezed-vacuum driving field via cavity–magnon and cavity–qubit beam-splitter interactions. The transfer is highly efficient, and the entanglement is robust against temperature in the optimal parameter regimes. We also deduce a new, to the best of our knowledge, mathematical method to analyze the dynamics of the magnon–qubit entanglement and some significant results are obtained. Our scheme can be implemented with experimentally feasible parameters and may provide guidance in designing hybrid quantum networks.

Manipulation of One‐Way Gaussian Steering via Quantum Correlated Microwave Fields

AbstractManipulation of one‐way Gaussian steering in macroscopic systems is outstandingly challenging in modern physics. In this paper, a cavity magnomechanical system is used which is composed of two spatially separate microwave cavities and two massive yttrium iron garnet (YIG) spheres in order for one‐way Gaussian steering. The two cavities are pumped by a two‐mode squeezed light, while both two YIG spheres are individually driven by a classical field at a red sideband with respect to the magnon mode. By creating different excitations for the two phonon modes, the systemic symmetry is broken and one‐way Gaussian steering with strong entanglement between two phonon modes induced by the deformation of YIG spheres is achieved. This finding may provide a novel method to manipulate asymmetric quantum steering between two long‐distance macroscopic objects which is of great importance for quantum information processing.

Phase-Modulated Cavity Magnon Polaritons as a Precise Magnetic Field Probe

We describe and operate a spin-magnetometer based on the phase modulation of cavity magnon polaritons. In this scheme a rf magnetic field is detected through the sidebands it induces on a pump, and the experimental configuration allows for a negligible pump noise and a high-frequency readout. The demonstrator setup, based on a copper cavity coupled to an yttrium iron garnet sphere hybrid system, reached a sensitivity of $2.0\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/\sqrt{\mathrm{Hz}}$ at 220 MHz, evading the pump noise and matching the theoretical predictions. An optimized setup can attain a rf magnetic field sensitivity of about $8\phantom{\rule{0.2em}{0ex}}\mathrm{fT}/\sqrt{\mathrm{Hz}}$ at room temperature. An orders of magnitude improvement is expected at lower temperatures, making this instrument one of the few magnetometers accessing the subfemtotesla limit.

Nonreciprocal high-order sidebands induced by magnon Kerr nonlinearity

We propose an effective approach for creating robust nonreciprocity of high-order sidebands, including the first-, second- and third-order sidebands, at microwave frequencies. This approach relies on magnon Kerr nonlinearity in a cavity magnonics system composed of two microwave cavities and one yttrium iron garnet (YIG) sphere. By manipulating the driving power applied on YIG and the frequency detuning between the magnon mode in YIG and the driving field, the effective Kerr nonlinearity can be strengthened, thereby inducing strong transmission non-reciprocity. More interestingly, we find the higher the sideband order, the stronger the transmission nonreciprocity marked by the higher isolation ratio in the optimal detuning regime. Such a series of equally-spaced high-order sidebands have potential applications in frequency comb-like precision measurement, besides structuring high-performance on-chip nonreciprocal devices.

Remote magnon entanglement between two massive ferrimagnetic spheres via cavity optomagnonics

Recent studies show that hybrid quantum systems based on magnonics provide a new and promising platform for generating macroscopic quantum states involving a large number of spins. Here, we show how to entangle two magnon modes in two massive yttrium-iron-garnet (YIG) spheres using cavity optomagnonics, where magnons couple to high-quality optical whispering gallery modes supported by the YIG sphere. The spheres can be as large as 1 mm in diameter and each sphere contains more than ${10}^{18}$ spins. The proposal is based on the asymmetry of the Stokes and anti-Stokes sidebands generated by the magnon-induced Brillouin light scattering in cavity optomagnonics. This allows one to utilize the Stokes and anti-Stokes scattering process, respectively, for generating and verifying the entanglement. Our work indicates that cavity optomagnonics could be a promising system for preparing macroscopic quantum states.

Coherent coupling between multiple ferrimagnetic spheres and a microwave cavity at millikelvin temperatures

The spin resonance of electrons can be coupled to a microwave cavity mode to obtain a photon-magnon hybrid system. These quantum systems are widely studied for both fundamental physics and technological quantum applications. In this article, the behavior of a large number of ferrimagnetic spheres coupled to a single cavity is put under test. We use second-quantization modeling of harmonic oscillators to theoretically describe our experimental setup and understand the influence of several parameters. The magnon-polariton dispersion relation is used to characterize the system, with a particular focus on the vacuum Rabi mode splitting due to multiple spheres. We combine the results obtained with simple hybrid systems to analyze the behavior of a more complex one, and show that it can be devised in such a way to minimize the degrees of freedom needed to completely describe it. By studying single-sphere coupling two possible size-effects related to the sample diameter have been identified, while multiple-spheres configurations reveal how to upscale the system. This characterization is useful for the implementation of an axion-to-electromagnetic field transducer in a ferromagnetic haloscope for dark matter searches. Our dedicated setup, consisting in ten 2 mm-diameter YIG spheres coupled to a copper microwave cavity, is used for this aim and studied at mK temperatures. Moreover, we show that novel applications of optimally-controlled hybrid systems can be foreseen for setups embedding a large number of samples.

Tunable multi-frequency optoelectronic oscillator based on a microwave photonic filter and an electrical filter

We propose and experimentally demonstrate a multi-frequency optoelectronic oscillator (OEO) based on the phase-modulation to intensity-modulation conversion. A microwave photonic filter incorporating an optical fiber Bragg grating Fabry–Perot filter and an electrical yttrium iron garnet (YIG) filter in two branches are used to select the oscillation modes of the OEO. By adjusting the wavelength of laser source or the central frequency of YIG filter, two frequencies can be tuned independently within a wide range. The single sideband phase noises of the generated frequencies are measured experimentally. Moreover, the OEO shows potential ability to achieve more frequencies oscillation by multiplexing more optical and electrical filters.

Exploring a quantum-information-relevant magnonic material: Ultralow damping at low temperature in the organic ferrimagnet V[TCNE

Quantum information science and engineering require novel low-loss magnetic materials for magnon-based quantum-coherent operations. The search for low-loss magnetic materials, traditionally driven by applications in microwave electronics near room temperature, has gained additional constraints from the need to operate at cryogenic temperatures for many applications in quantum information science and technology. Whereas yttrium iron garnet (YIG) has been the material of choice for decades, the emergence of molecule-based materials with robust magnetism and ultra-low damping has opened new avenues for exploration. Specifically, thin films of vanadium tetracyanoethylene (V[TCNE]x) can be patterned into the multiple, connected structures needed for hybrid quantum elements and have shown room-temperature Gilbert damping (α = 4 × 10−5) that rivals the intrinsic (bulk) damping otherwise seen only in highly polished YIG spheres (far more challenging to integrate into arrays). Here, the authors present a comprehensive and systematic study of the low-temperature magnetization dynamics for V[TCNE]x thin films, with implications for their application in quantum systems. These studies reveal a temperature-driven, strain-dependent magnetic anisotropy that compensates the thin-film shape anisotropy and the recovery of a magnetic resonance linewidth at 5 K that is comparable to room-temperature values (roughly 2 G at 9.4 GHz). The authors can account for these variations of the V[TCNE]x linewidth within the context of scattering from very dilute paramagnetic impurities and anticipate additional linewidth narrowing as the temperature is further reduced.

One-way Einstein–Podolsky–Rosen steering of macroscopic magnons with squeezed light

We present to use the squeezed light and the thermal effect to induce the one-way steering of magnon modes from two separated yttrium–iron–garnet spheres respectively placed in two microwave cavities. Based on the squeezed-reservoir engineering, the reduced master equation of magnon modes is derived by adiabatically eliminating the variables of cavity modes in the bad-cavity limit. Our results reveal that the steady-state steerable correlation of distant macroscopic objects is effectively achieved, and the steering direction could be tunable with the choice of the experimental parameters such as the squeezing degree, the coupling strengths, and the thermal magnon occupations. The responsible mechanism is due to the delicate interplay between the squeezing reservoir and the original dissipative process of the cavity fields. The striking feature of our scheme is that it relaxes the requirement of accurate control of the system. Moreover, the scheme is focused on the asymmetric Einstein–Podolsky–Rosen steering of macroscopic magnons and it could be extended to more magnon modes, which may provide a novel method for studying the macroscopic quantum phenomena and devising the active quantum information devices.

Phase-controlled multimagnon blockade and magnon-induced tunneling in a hybrid superconducting system

We study the multimagnon blockade and magnon-induced tunneling in the hybrid ferromagnet-superconductor system, where a magnon mode representing the collective motion of spins in the yttrium iron garnet (YIG) sphere is coupled with a three-level $\mathrm{\ensuremath{\Delta}}$-type fluxonium qubit via the virtual-photon excitation from the microwave cavity. By appropriately choosing the parameters, the single magnon blockade, multimagnon blockade including two- and three-magnon blockades, and magnon-induced tunneling could be achieved. Fortunately, the switch from magnon blockade to magnon-induced tunneling could be obtained via controlling the overall phase of the loop transition determined by the driving fields. Furthermore, the single-magnon blockade could be transformed into a multimagnon blockade via the phase modulation. The scheme we present may provide an alternative method to manipulate the few-magnon states and have potential applications in quantum communication and quantum information processing.

Enhanced Sensing of Weak Anharmonicities through Coherences in Dissipatively Coupled Anti-PT Symmetric Systems.

In the last few years, the great utility of exceptional points in sensing linear perturbations has been recognized. However, physical systems are inherently anharmonic and macroscopic physics is most accurately described by nonlinear models. Considering the multitude of semiclassical and quantum effects ensuing from nonlinear interactions, the sensing of anharmonicities is a prerequisite to the primed control of these effects. Here, we propose an expedient sensing scheme relevant to dissipatively coupled anti parity-time (anti-PT) symmetric systems and customized for the fine-grained estimation of anharmonic perturbations. The sensitivity to anharmonicities is derived from the coherence between two modes induced by a common vacuum. Owing to this coherence, the linear response acquires a pole on the real axis. We demonstrate how this singularity can be exploited for the enhanced sensing of very weak anhamonicities at low pumping rates. Our results are applicable to a wide class of systems, and we specifically illustrate the remarkable sensing capabilities in the context of a weakly anharmonic yttrium iron garnet sphere interacting with a cavity via a tapered fiber waveguide. A small change in the anharmonicity leads to a substantial change in the induced spin current.

Precisely tunable heterodyne-injection-locked dual-loop optoelectronic oscillator

A precisely tunable heterodyne-injection-locked dual-loop optoelectronic oscillator (HIL-DL OEO) is analyzed and experimentally demonstrated. The primary loop, utilizing a narrow bandpass filter, generates a frequency-fixed signal, and the secondary loop, incorporating a yttrium iron garnet filter, outputs the tunable signal. The oscillating signal in each loop experiences frequency translation at an external frequency translation module (FTM) and is then fed to the other loop. The frequency translation at the FTM, which is composed of two mixers and a power splitter, is realized with the help of a tunable low-frequency signal. Thanks to the low-frequency signal, the oscillation frequency in the secondary loop would vary accordingly under injection locking.

Cavity magnomechanical storage and retrieval of quantum states

We show how a quantum state in a microwave cavity mode can be transferred to and stored in a phononic mode via an intermediate magnon mode in a magnomechanical system. For this we consider a ferrimagnetic yttrium iron garnet (YIG) sphere inserted in a microwave cavity, where the microwave and magnon modes are coupled via a magnetic-dipole interaction and the magnon and phonon modes in the YIG sphere are coupled via magnetostrictive forces. By modulating the cavity and magnon detunings and the driving of the magnon mode in time, a stimulated Raman adiabatic passage-like coherent transfer becomes possible between the cavity mode and the phonon mode. The phononic mode can be used to store the photonic quantum state for long periods as it possesses lower damping than the photonic and magnon modes. Thus our proposed scheme offers a possibility of using magnomechanical systems as quantum memory for photonic quantum information.

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.