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Journal of Physics B Atomic Molecular and Optical Physics

Entanglement between a macroscopic displacement and microwave fields from levitated macromagnet

Bao Gu, Guolong Li

Published Jul 10, 2025• 0 citations
Publisher

Abstract

Abstract This work looks at the quantum entanglement between the cavity microwave and center-of-mass motion of a ferrimagnetic yttrium-iron-garnet (YIG) sphere levitated in two microwave cavities. In such a cavity magnomechanical (CMM) system, the magnons, i.e. quanta of collective spin-wave excitations in the YIG sphere, are coupled to a center-of-mass displacement via intense CMM coupling in a strongly driven cavity, and are simultaneously coupled to the other cavity via magnetic dipole interaction. We reveal that the detuning condition is necessary to improve the mediation effect of the magnon for generating macroscopic entanglement. In particular, this center-of-mass motion can be adjusted by suitable levitation technology, unlike the mechanical deformation limited by the fixed structure of the YIG sphere in a standard CMM system. We also indicate that the entanglement via the unique CMM coupling is independent of the size and mass of the YIG sphere, and it is beneficial to explore the macroscopic entanglement effect in combination with size-independent cooling. These findings suggest that our scheme may open up an alternative and novel direction in the exploration and application of macroscopic quantum effects.

DOI
10.1088/1361-6455/adeddc

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Abstract This work looks at the quantum entanglement between the cavity microwave and center-of-mass motion of a ferrimagnetic yttrium-iron-garnet (YIG) sphere levitated in two microwave cavities. In such a cavity magnomechanical (CMM) system, the magnons, i.e. quanta of collective spin-wave excitations in the YIG sphere, are coupled to a center-of-mass displacement via intense CMM coupling in a strongly driven cavity, and are simultaneously coupled to the other cavity via magnetic dipole interaction. We reveal that the detuning condition is necessary to improve the mediation effect of the magnon for generating macroscopic entanglement. In particular, this center-of-mass motion can be adjusted by suitable levitation technology, unlike the mechanical deformation limited by the fixed structure of the YIG sphere in a standard CMM system. We also indicate that the entanglement via the unique CMM coupling is independent of the size and mass of the YIG sphere, and it is beneficial to explore the macroscopic entanglement effect in combination with size-independent cooling. These findings suggest that our scheme may open up an alternative and novel direction in the exploration and application of macroscopic quantum effects.
Entanglement formation between the magnons as the internal degrees of freedom and the center-of-mass motion (CM) as the external degrees of freedom of a levitated yttrium iron garnet (YIG) sphere in a cavity-magnomechanical system is studied. Here, we propose a scheme for generating magnon-CM entanglement independent from the mass and size of the sphere in the hybrid magnonic system by driving the magnon with the parametric amplification. First, we show that the power and frequency of the driving field significantly affect this entanglement, since the driving field increases effective magnon-CM coupling. But, by increasing the magnon damping rate, this entanglement considerably decreases. Moreover, in the next step, we demonstrate the manipulation and enhancement of this entanglement by driving the magnon into the squeezed state. Our results present an approach for preparing quantum states and may find promising applications in the quantum metrology and sensing.
We demonstrate nonreciprocal macroscopic entanglement between magnon modes in two yttrium-iron-garnet (YIG) spheres induced by the Kerr effect stemming from magnetocrystalline anisotropy. The two YIG spheres with different sizes are placed in a microwave cavity, and the magnon modes couple to the microwave cavity photons by the magnetic dipole interaction. The microwave cavity can be adiabatically eliminated by far detuning from the magnon modes, and thus mediates the indirect interaction between two magnon modes. The magnon Kerr nonlinearity of the small YIG sphere is enhanced by the appropriate drive. Meanwhile, the sign of the Kerr coefficient can be manipulated by changing the direction of the bias magnetic field, in turn causing the nonreciprocity of magnon-magnon entanglement. We numerically analyze the optimal parameter regions for generating the entanglement. The properties of the nonreciprocal entanglement are explored by analyzing the defined bidirectional contrast ratio, which reveals the different strategies for controlling the nonreciprocity of the entanglement. The presented scheme provides an alternative method for the nonreciprocal macroscopic entanglement and may have potential applications in nonreciprocal quantum devices and macroscopic quantum effects.
The cavity-mediated coupling between magnons in an yttrium-iron-garnet (YIG) sphere and a superconducting qubit has recently been demonstrated as a new platform for preparing macroscopic quantum states. Here, based on this system, we propose to entangle two magnon modes in two YIG spheres by driving the qubit with a two-tone field and by appropriately choosing the frequencies and strengths of the two driving fields. We show that strong entanglement can be achieved with fully feasible parameters. We further provide a detection scheme for experimentally verifying the entanglement. Our results indicate that macroscopic entanglement between two magnon modes in two millimeter-sized YIG spheres, involving more than 101810^{18}1018 spins, can be realized using currently available parameters, which finds promising applications in fundamental studies, such as macroscopic quantum mechanics and the test of unconventional decoherence theories.
We theoretically propose a cavity magnomechanical system with a levitated yttrium iron garnet sphere to study the entanglement characteristics between subsystems. The system consists of microwave photon, magnon, and mechanical phonon modes, where the photon and magnon modes can be driven by external microwave sources. We find that with the appropriate choice of the suspension position, the effective couplings between the cavity field and the magnon and phonon modes can be established, thus inducing the generation of bipartite entanglement and genuine tripartite entanglement in the system. Further, we also analyze in detail the influences of the radius of the sphere, the detunings of the cavity and magnon modes, the driving power, the frequency of the phonon mode, and the environment temperature on the characteristics of the quantum entanglement. The results obtained here indicate that the bipartite and tripartite entanglements can be manipulated by changing the radius and the oscillation frequency of the sphere in addition to changing the parameters of the cavity field, and therefore, the levitated magnomechanical system has a potential application in the study of macroscopic quantum phenomena.
We theoretically propose a scheme to realize quantum entanglement between two center-of-mass motion (CM) as the external degrees of freedom of two separated levitated yttrium iron garnet spheres. The microwave cavity field is introduced to bridge the interaction between the two separated micromagnet spheres. The optimal condition for getting entanglement between the two CM modes with and without effective cavity-magnon interaction cases are investigated. It is found that the entanglement between two CM modes could be obtained by choosing the appropriate magnon detunings for each case. The effect of the coupling strength and the thermal occupation on the entanglement are also discussed. To realize the entanglement between to CM modes, it is necessary to balance the related parametric interaction and beam splitter interaction. The results show that the CM-CM entanglement is robust against the thermal noise. This scheme would be valuable for quantum network generation and quantum information processing.
Abstract A scheme is proposed for generating controllable quantum correlations in a cavity‐magnomechanical system comprising a microwave cavity and two yttrium iron garnet (YIG) spheres. A single‐mode squeezed vacuum field drives the cavity, while a red‐detuned field excites the magnon modes within the YIG spheres. Activating the magnetostrictive effect in the spheres introduces phonon modes through geometric deformation. By linearizing the system dynamics and introducing slowly moving operators to neglect high‐frequency oscillatory terms, the correlated noise from the single‐mode squeezed vacuum field can be effectively transferred between the two magnon modes and the phonon modes. Control of the cavity‐magnon coupling rate breaks the system's symmetry, enabling the generation of tunable quantum squeezing, entanglement, and one‐way quantum steering. This tunability facilitates the development of quantum information processing platforms, offering a promising framework for advancing quantum information technologies.