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arXiv:2605.06297 · Physical Review A

Macroscopic entanglement between two magnon modes via two-tone driving of a superconducting qubit

Rong-Can Yang, Gang Liu, Gen Li, Jie Li

quant-phcond-mat.mes-hallphysics.opticsSubmitted May 7, 2026• Announced May 8, 2026• 0 citations
v1 · May 7, 2026v2 · Sep 25, 2026
arXivHTMLPDF

Abstract

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 $10^{18}$ 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.

Journal reference
Phys. Rev. A 114, 043707 (2026)
DOI
10.1103/jtyx-xsgc

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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 propose a scheme for preparing magnon squeezed states in a hybrid cavity-magnon-qubit system. The system consists of a microwave cavity that simultaneously couples to a magnon mode of a macroscopic yttrium-iron-garnet sphere via the magnetic-dipole interaction and to a transmon-type superconducting qubit via the electric-dipole interaction. By far detuning from the magnon-qubit system, the microwave cavity is adiabatically eliminated. The magnon mode and the qubit then get effectively coupled via the mediation of virtual photons of the microwave cavity. We show that by driving the qubit with two microwave fields and by appropriately choosing the drive frequencies and strengths, magnonic parametric amplification can be realized, which leads to magnon quadrature squeezing with the noise below vacuum fluctuation. We provide optimal conditions for achieving magnon squeezing, and moderate squeezing can be obtained using currently available parameters. The generated squeezed states are of a magnon mode involving more than 1018{10}^{18}1018 spins and thus macroscopic quantum states. This work may find promising applications in quantum information processing and high-precision measurements based on magnons and in the study of macroscopic quantum states.
The cavity-magnon-qubit system has recently been demonstrated as a new platform for preparing macroscopic quantum states in magnonic systems. Here, we propose to prepare a two-mode magnonic cat state, which is also a non-Gaussian entangled state, based on this practical system involving two yttrium-iron-garnet (YIG) spheres and a superconducting qubit coupled to a common microwave cavity. By adiabatically eliminating the cavity and resonantly driving the qubit, an effective magnon-qubit conditional-displacement interaction is achieved. Further working in the magnon-magnon strong-coupling regime and considering two identical magnon frequencies and coupling strengths to the cavity, two hybridized magnon modes are formed, of which the bright mode is prepared in a cat state after a projective measurement on the qubit, while the dark mode remains in its initial vacuum state. Such a state corresponds to a two-mode cat state of two original magnon modes, which share strong non-Gaussian entanglement. We also discuss practical dissipation and dephasing effects on the cat state. The results indicate that strong nonclassicality and non-Gaussian entanglement are present in the two-mode cat state using fully feasible parameters.
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.
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 1018{10}^{18}1018 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.
The generation of robust entanglement in quantum system arrays is a crucial aspect of the realization of efficient quantum information processing. Recently, the field of quantum magnonics has garnered significant attention as a promising platform for advancing in this direction. In our proposed scheme, we utilize a one-dimensional array of coupled cavities, with each cavity housing a single yttrium iron garnet (YIG) sphere coupled to the cavity mode through magnetic dipole interaction. To induce entanglement between YIGs, we employ a local squeezed drive, which provides the necessary nonlinearity for entanglement generation. Our results demonstrate the successful generation of bipartite and tripartite entanglement between distant magnon modes, all achieved through a single quantum drive. Furthermore, the steady-state entanglement between magnon modes is robust against magnon dissipation rates and environment temperature. Our results may lead to applications of cavity-magnon arrays in quantum information processing and quantum communication systems.
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.