Yttrium Iron Garnet Sphere Research Articles

Generation of robust optical entanglement in cavity optomagnonics.

We propose a scheme to realize robust optical entanglement in cavity optomagnonics, where two optical whispering gallery modes (WGMs) couple to a magnon mode in a yttrium iron garnet (YIG) sphere. The beam-splitter-like and two-mode squeezing magnon-photon interactions can be realized simultaneously when the two optical WGMs are driven by external fields. Entanglement between the two optical modes is then generated via their coupling with magnons. By exploiting the destructive quantum interference between the bright modes of the interface, the effects of initial thermal occupations of magnons can be eliminated. Moreover, the excitation of the Bogoliubov dark mode is capable of protecting the optical entanglement from thermal heating effects. Therefore, the generated optical entanglement is robust against thermal noise and the requirement of cooling the magnon mode is relaxed. Our scheme may find applications in the study of magnon-based quantum information processing.

Quantum entanglement generation on magnons assisted with microwave cavities coupled to a superconducting qubit

We present protocols to generate quantum entanglement on nonlocal magnons in hybrid systems composed of yttrium iron garnet (YIG) spheres, microwave cavities and a superconducting (SC) qubit. In the schemes, the YIGs are coupled to respective microwave cavities in resonant way, and the SC qubit is placed at the center of the cavities, which interacts with the cavities simultaneously. By exchanging the virtual photon, the cavities can indirectly interact in the far-detuning regime. Detailed protocols are presented to establish entanglement for two, three and arbitrary N magnons with reasonable fidelities.

Quantum coherence versus quantum correlations in a double cavity magnomechanical system

In this paper, we investigate a system composed of two spatially separated cavities, each with a magnon mode of a yttrium iron garnet (YIG) sphere coupled to a microwave (MW) cavity and phonon modes, respectively, via linear beam splitter and magnetostrictive interactions. In addition, two-mode squeezed vacuum fields drive the two cavities. We investigate and compare the behavior of three nonclassicality indicators in two subsystems (i.e., magnon–magnon and phonon–phonon) under the influences of the temperature, the cavity–magnon damping rate, and the magnomechanical coupling rate. We use the entanglement of formation (EoF) to measure the degree of entanglement, the Gaussian quantum discord (GQD) to characterize the quantum correlations beyond entanglement and Gaussian quantum coherence (GQC) to quantify coherence. Considering that the quantifiers share the same entropic definition, we compare the three quantifiers and test the validity of the hypothesis that quantum states with nonzero discord are inherently entangled. We find, on the one hand, that both GQC and GQD exhibit freezing behavior and that they are more robust to the decoherence effect than the EoF. On the other hand, the EoF and the GQD are always upper bounded by GQC, and there is no simple dominance relationship between EoF and GQD; hence these two quantifiers should not be compared. The effect of other parameters is also discussed in detail.

Nonreciprocal sideband responses in a spinning microwave magnomechanical system.

Nonreciprocal sideband responses in a spinning microwave magnomechanical system consists of a spinning resonator coupled with a yttrium iron garnet sphere are proposed. We show that the efficiency of sideband generation can be enhanced in one driving direction but restrained in the opposite. This nonreciprocity results from Sagnac effect induced by the spinning resonator, leading to asymmetric magnonic responses in two different driving directions. Beyond the conventional linearized description, the properties of nonreciprocal two-color second-order sideband are demonstrated. By adjusting Sagnac-Fizeau shift and the power of control field, the degree of asymmetric magnonic responses can be strengthened, therefore causing stronger nonreciprocity of sideband. Especially, for the case of strong Sagnac-Fizeau shift and the control field, high level of efficiency and isolation ratio of sideband are achieved simultaneously and the operational bandwidth of strong nonreciprocity can be expanded. Our proposal provides an effective avenue for the manipulation of the nonreciprocity of sideband and has potentially practical applications in on-chip microwave isolation devices and magnon-based precision measurement.

Interactive entanglement in hybrid opto-magno-mechanics system

We present a novel cavity opto-magno-mechanical hybrid system to generate entanglements among multiple quantum carriers, such as magnons, mechanical resonators, and cavity photons in both the optical and microwave domains. Two Yttrium iron garnet (YIG) spheres are embedded in two separate microwave cavities which are joined by a communal mechanical resonator. Because the microwave cavities are separate, the ferromagnetic resonate frequencies of two YIG spheres can be tuned independently, as well as the cavity frequencies. We show that entanglement can be achieved with experimentally reachable parameters. The entanglement is robust against environmental thermal noise, owing to the mechanical cooling process achieved by the optical cavity. The maximum entanglement among different carriers is achieved by optimizing the parameters of the system. The individual tunability of the separated cavities allows us to independently control the entanglement properties of different subsystems and establish quantum channels with different entanglement properties in one system. This work could provide promising applications in quantum metrology and quantum information tasks.

Nonclassicality of dissipative cavity optomagnonics in the presence of Kerr nonlinearities

The phenomena of photon and magnon blockade, and nonclassicality which are the key ingredient for quantum enhanced technologies, can be considered as resources in quantum information processing. This paper deals with the study of nonclassicality in a lossy optomagnonic microcavity enclosed by Kerr medium, with considering different sources of dissipation. The system contains a ferromagnetic YIG sphere coupled to two optical modes in a microcavity, with photonic and magnonic Kerr nonlinearity in the presence of magnonic and photonic losses. Considering the Heisenberg-Langevin approach, we obtain the dynamics of the second-order correlation functions (CFs) to observe the phenomenon of photon and magnon blockade (PMB), and the Cauchy-Schwarz inequality (CSI) to find the nonclassicality of the system. We then discuss the effects of magnon-photon coupling strength and different sources of dissipation on the temporal behavior of the mentioned criteria. Looking at the numerical results, we find that the depth and the domain of antibunching behavior significantly depend on the value of the thermal average photon (magnon) number. The phenomenon of perfect PMB may also be observed in the presence of dissipation at the low-temperature regime where the equilibrium thermal photon (magnon) occupation number approaches zero, i.e. T → 0. Moreover, we see a strong anticorrelation between the photonic and magnonic modes and the optical modes, too. Furthermore, it can be found that the phenomenon of PMB blockade as well as antibunching can be observed at cryogenic temperatures.

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system

We theoretically explore the tunability of magnomechanically induced transparency (MMIT) phenomenon and fast-slow light effect in a hybrid cavity magnomechanical system in which a high-quality yttrium iron garnet (YIG) sphere and an atomic ensemble are placed inside a microwave cavity. In the probe output spectrum, we can observe magnon-induced transparency (MIT) and MMIT due to the photon-magnon and phonon-magnon couplings. We further investigate the effect of atomic ensemble on the absorption spectrum. The results show that better transparency can be obtained by choosing appropriate atomic ensemble parameters. We give an explicit explanation for the mechanism of the Fano resonance phenomenon. Moreover, we discuss phenomena of slow-light propagation. The maximum group delay increases significantly with the increasing atom–cavity coupling strength, and the conversion between slow light and fast light can also be achieved by adjusting the atom–cavity coupling strength. These results may have potential applications for quantum information processing and high precision measurements.

Magnonic Einstein-de Haas Effect: Ultrafast Rotation of Magnonic Microspheres.

Magnons, collective spin excitations in magnetic crystals, have attracted much interest due to their ability to couple strongly to microwaves and other quantum systems. In compact magnetic crystals, we show that there are magnonic modes that can support orbital angular momentum and that these modes can be driven by linearly polarized microwave fields. Because of conservation of angular momentum, exciting such magnon modes induces a mechanical torque on the crystal. We study a levitated magnetic crystal, a yttrium iron garnet (YIG) microsphere, where such orbital angular momentum magnon modes are driven by microwaves held in a microwave high-Q microwave cavity. We find that the YIG sphere experiences a mechanical torque and can be spun up to ultralarge angular speeds exceeding 10GHz.

Nonlinear pumping induced multipartite entanglement in a hybrid magnon cavity QED system

We present a proposal to produce bipartite and tripartite entanglement in a hybrid magnon cavity QED system. Two macroscopic yttrium iron garnet (YIG) spheres are coupled to a single-mode microwave cavity, where the cavity photons are generated via a two-photon process induced by a strong pump field. Using mean-field theory, we show that nonlinear pumping can result in strong bipartite entanglement between the cavity photon and magnon under two conditions, i.e., ${\ensuremath{\delta}}_{c}{\ensuremath{\delta}}_{m}=2{g}^{2}$ and ${\ensuremath{\delta}}_{c}=\ensuremath{-}{\ensuremath{\delta}}_{m}$. For the latter one, we also show the possibility for producing bipartite entanglement between two magnon modes as well as tripartite entanglement among three modes. Combining these two conditions, we further derive a third condition, i.e., ${\ensuremath{\delta}}_{m}^{2}\ensuremath{-}{\ensuremath{\phi}}^{2}+2{g}^{2}=0$, where tripartite entanglement can be achieved when two magnon modes have different resonant frequencies.

Engineering and manipulating topological edge states in a tunable magnon chain

We propose an effective scheme for manipulating the topological edge states in a tunable magnon chain with yttrium iron garnet spheres. In this setup, the coupling interactions between two magnons are realized indirectly via a split-ring resonator. With these indirect magnon–magnon couplings, we design a finite dimer chain with the Su–Schrieffer–Heeger Hamiltonian, show that Rabi oscillations between the left and right edge modes may be observed in an even-numbered case. For comparison, the characteristic of the edge state in an odd-numbered case is different, and we find that topological pumping of the edge state can be achieved via an adiabatic passage protocol. More importantly, we theoretically demonstrate that both the Rabi dynamics and the adiabatic pumping protocol could be used for long-range quantum state transfer, but the adiabatic-pumping transfer is particularly robust against intensity noise. This work provides a promising platform for creating topological devices, which may further be applied in quantum information processing.

Chirality-induced one-way quantum steering between two waveguide-mediated ferrimagnetic microspheres

One-way quantum steering is of importance for quantum technologies, such as secure quantum teleportation. In this paper, we study the generation of one-way quantum steering between two distant yttrium iron garnet (YIG) microspheres in chiral waveguide electromagonics. We consider that the magnon mode with the Kerr nonlinearity in each YIG sphere is chirally coupled to left- and right-propagating guided photons in the waveguide. We find that quantum steering between the magnon modes is absent with non-chirality but is present merely in the form of one way (i.e., one-way steering) when the chirality occurs. The maximal achievable steering is obviously improved as the chirality degree increases. We further find that when the waveguide's outputs are subjected to continuous homodyne detection, the steering can be considerably enhanced and asymmetric steering with strong entanglement can also be achieved by tuning the chirality. Our study shows that chirality can be explored to effectively realize one-way quantum steering. Compared to other studies on achieving asymmetric steering via controlling intrinsic dissipation, e.g. cavity loss rates, our scheme merely depends on the chirality enabled via positioning the micromagnets in the waveguide and is continuously adjustable and experimentally more feasible.

Kerr-Nonlinearity-Triggered Nonclassicality of Magnons in a Photon-Magnon Coupling System

Hybrid quantum systems have attracted much attention due to the fact that they combine the advantages of different physical subsystems. Cavity QED (cavity quantum electrodynamics) with magnons is a hybrid quantum systems that combines a YIG (Yttrium Iron Garnet) sphere and a 3D (three-dimensional) rectangular microwave cavity. Based on this hybrid photon-magnon system, we obtain an approximate analytic solution by the RWA (rotating wave approximation) with an ingenious transformation. After skillfully diagonalizing the Hamiltonian, we show that the Kerr-nonlinearity interactions could yield a negativity value of the Wigner function, periodic quadrature squeezing effects, antibunching property, and field nonclassicality in the magnon. Our work may stimulate the study of nonclassicality of photon-magnon coupling systems and its potential applications in quantum information processing.

Entangling two cavity modes and squeezing magnon mode via parametric down-conversion

A scheme to entangle two cavity modes and squeeze magnon mode in a magnon–cavity QED system is presented, where the two microwave cavity modes are coupled to a massive yttrium iron garnet sphere. The nonlinearity used in our system originates from parametric down-conversion. By using the mean field approximation and employing experimentally feasible parameters, we indicate that the entanglement between squeezed cavity mode and magnon mode can be transferred to the other cavity mode and magnon mode, and then the two cavity modes get entangled. Meanwhile, the magnon mode is squeezed in our QED system. Furthermore, we show that it is a good way to enhance entanglement and squeezing by increasing the nonlinear gain. Our results denote that magnon–cavity QED system is a powerful platform for studying macroscopic quantum phenomena, which illustrates a new approach to photon–photon entanglement and magnon squeezing.

Tunable magnon antibunching via degenerate three-wave mixing in a hybrid ferromagnet–superconductor system

We propose a scheme for achieving magnon antibunching in a hybrid ferromagnet–superconductor system, where the magnons excited in two yttrium iron garnet (YIG) spheres couple the different levels of a cyclic three-level superconducting qubit by eliminating two perpendicular microwave cavity modes. With the aid of the three-level system, we find that the magnon antibunching can be achieved in a weak coupling regime via the degenerate three-wave mixing process. Moreover, it is found that the magnon antibunching inside a YIG2 sphere can be effectively regulated by manipulating the YIG1 sphere, for instance, the coupling strength of the YIG1 sphere and qubit and the driving strengths of the system. This work provides an alternative scheme for constructing the single magnon source based on the ferromagnet–superconductor technology and is conducive to studying the quantum properties of magnons.

Magnonic frequency combs based on the resonantly enhanced magnetostrictive effect

A magnonic counterpart to optical frequency combs is vital for high-precision magnonic frequency metrology and spectroscopy. Here, we present an efficient mechanism for the generation of robust magnonic frequency combs in a yttrium iron garnet (YIG) sphere via magnetostrictive effects. We show that magnonic and vibrational dynamics in the ferrimagnetic sphere can be substantively modified in the presence of magnetostrictive effects, which results in degenerate and non-degenerate magnonic four-wave mixing and frequency conversion. Particularly, resonantly enhanced magnetostrictive effects can induce phonon laser action above a threshold, which leads to significant magnonic nonlinearity and enables a potentially practical scheme for the generation of robust magnonic frequency combs. Numerical calculations of both magnonic and phononic dynamics show excellent agreement with this theory. These results deepen our understanding of magnetostrictive interaction, open a novel and efficient pathway to realize magnonic frequency conversion and mixing in a magnonic device, and provide a sensitive tool for precision measurement.

Nonreciprocal transmission in a four-mode cavity magnonics system

We propose a scheme to create optical nonreciprocal transmission in a double-cavity magnonics system, where one yttrium iron garnet sphere is placed in one of the cavities and a mechanical oscillator is shared by the coupled double microwave cavities. By manipulating the magnon–microwave photon coupling, we reveal the nonreciprocal propagation of electromagnetic fields at microwave frequencies in red and blue-detuned regimes. Furthermore, the nonreciprocal isolation ratio and group delay are analyzed. This scheme can inspire methods for constructing nonreciprocal devices.

Hybrid magnon-atom entanglement and magnon blockade via quantum interference

In this paper, we propose a quantum interference mediated control of switching between magnon-atom entanglement and magnon blockade. A three-level $\mathrm{\ensuremath{\Lambda}}$ configuration atomic ensemble and a yttrium iron garnet sphere are simultaneously coupled to a microwave cavity mode through magnetic dipole interaction. By applying two strong fields to drive the atoms, the resonant coupling between a dressed-state atomic transition and the magnon mode, without direct interaction, is established by adiabatically eliminating the cavity field. Interestingly, the anti-Jaynes-Cummings (JC) interaction and the JC interaction are alternatively formed when the atoms are trapped into different superposition states induced by quantum interference, causing the appearance of hybrid magnon-atom entanglement and magnon quantum blockade, respectively. The coherent-controlled hybrid magnon-atom entanglement and magnon blockade may find potential applications in quantum information processing.

Parametric-amplification-induced nonreciprocal magnon laser.

We theoretically propose a scheme to achieve all-optical nonreciprocal magnon lasing action in a composite cavity optomagnonical system considering of a yttrium iron garnet sphere coupled to a parametric resonator. The magnon lasing behavior can be engendered via the magnon-induced Brillouin scattering process in the cavity optomagnonical system. By unidirectionally driving the χ(2)-nonlinear resonator with a classical coherent field, the squeezed effect occurs only in the selected direction due to the phase-matching condition, resulting in asymmetric detuning between the two resonators, which is the physical mechanism to generate a nonreciprocal magnon laser. We further examine the gain factor and power threshold of the magnon laser. Moreover, the isolation rate can reach 21 dB by adjusting the amplitude of the parametric amplification. Our work shows a path to obtain an all-optical nonreciprocal magnon laser, which provides a means for the preparation of a coherent magnon laser and laser protection.

Controlling quantum coherence and entanglement in cavity magnomechanical systems

We investigate theoretically macroscopic quantum coherence and tripartite entanglement in a three-mode magnomechanical system with a yttrium iron garnet sphere, which is simultaneously driven by a magnetic pump and a microwave field pump to establish an effective magnomechanical coupling. We discuss mainly the dependence of quantum properties on the driving power, the cavity field detuning and decay, the magnomechanical coupling strength, the bias magnetic field, and the temperature of an environment. It is found that the quantum coherence of the system can be attained easily in a large range of parameters. In contrast, tripartite photon-magnon-phonon entanglement can only be realized in a relatively small range of optical and magnetic parameters. In particular, the quantum coherence of the mechanical mode can be larger than that of the photon and magnon modes, which means that the environmental incoherence of the mechanical mode in the cavity magnomechanical system can be suppressed significantly. These results may help manipulate simultaneously the macroscopic quantum coherence and the tripartite entanglement of massive objects in coupled magnomechanical system, which may have potential applications for realizing highly tunable information processing through the flexible control of quantum properties.

Optomagnonically tunable whispering gallery cavity laser wavelength conversion

We achieve laser wavelength conversion in an optomagnonical whispering gallery cavity by adjusting the strength of the applied static magnetic field. Numerical simulations are carried out on a yttrium iron garnet (YIG) sphere under different cavity quality factors or coupling strength. It is found that a high cavity quality factor will not always mean a high cavity excitation field for Gaussian lasers with finite linewidth. On state of the art, the high cavity quality factor will always mean the higher lightwave conversion rate. In addition, we also find that increasing the mode coupling strength is beneficial to the conversion of the laser. Our study provides new insights into generation of highly precise tunable coherent light.