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arXiv:2602.19671 · Nature Communications

Magnon squeezing in the quantum regime

Yuan-Chao Weng, Da Xu, Zhen Chen, Li-Zhou Tan, Xu-Ke Gu, Jie Li, Hai-Feng Yu, Shi-Yao Zhu, Xuedong Hu, Franco Nori, J. Q. You

quant-phSubmitted Feb 23, 2026• Announced Feb 24, 2026• 18 citations
arXivHTMLPDF

Abstract

Squeezed states, crucial for quantum metrology and emerging quantum technologies, have been demonstrated in various platforms, but quantum squeezing of magnons in macroscopic spin systems remains elusive. Here we report the experimental observation of quantum-level magnon squeezing in a millimeter-scale yttrium iron garnet (YIG) sphere. By engineering a strong dispersive magnon-superconducting qubit coupling via a microwave cavity, we implement a significant self-Kerr nonlinearity to generate squeezed magnon states with their mean magnon number less than one. Harnessing a magnon-assisted Raman process, we perform Wigner tomography, revealing quadrature variances of $\sim\!0.8$ ($\sim\!1.0$~dB squeezing) relative to the vacuum. These results lay the groundwork for quantum nonlinear magnonics and promise potential applications in quantum metrology.

Journal reference
Nat Commun 17, 2679 (2026)
DOI
10.1038/s41467-026-69312-4
Comments
9 pages, 4 figures

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Squeezed states, crucial for quantum metrology and emerging quantum technologies, have been demonstrated in various platforms, but quantum squeezing of magnons in macroscopic spin systems remains elusive. Here we report the experimental observation of quantum-level magnon squeezing in a millimeter-scale yttrium iron garnet (YIG) sphere. By engineering a strong dispersive magnon-superconducting qubit coupling via a microwave cavity, we implement a significant self-Kerr nonlinearity to generate squeezed magnon states with their mean magnon number less than one. Harnessing a magnon-assisted Raman process, we perform Wigner tomography, revealing quadrature variances of ∼ ⁣0.8\sim\!0.8∼0.8 (∼ ⁣1.0\sim\!1.0∼1.0~dB squeezing) relative to the vacuum. These results lay the groundwork for quantum nonlinear magnonics and promise potential applications in quantum metrology.
Abstract We propose a scheme to generate squeezed states in a cross-shaped cavity magnonics system by Kerr effect originating from the magnetocrystalline anisotropy. The system consists of two microwave cavities and a yttrium iron garnet sphere supporting a magnon mode embodying the collective spin motion, and each cavity mode is coupled with the magnon mode through the magnetic-dipole interaction. It is demonstrated that simultaneous squeezing of the two microwave cavity modes and the magnon mode can be achieved due to Kerr nonlinearity, and the squeezing of the magnon mode can break the 3 dB limit. By utilizing a Bogoliubov transformation, a new perspective on the underlying physical mechanism for the generation of the squeezing using Kerr nonlinearity is provided. Moreover, we also demonstrate the strong robustness of the magnon mode’s squeezing against the system dissipation and environmental temperature. The present scheme provides a promising platform for quantum information processing, holding significant implications for quantum metrology and precision measurement.
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.
Nonclassical quantum states are the pivotal features of a quantum system that differs from its classical counterpart. However, the generation and coherent control of quantum states in a macroscopic spin system remain an outstanding challenge. Here we experimentally demonstrate the quantum control of a single magnon in a macroscopic spin system (i.e., 1 mm-diameter yttrium-iron-garnet sphere) coupled to a superconducting qubit via a microwave cavity. By tuning the qubit frequency in situ via the Autler-Townes effect, we manipulate this single magnon to generate its nonclassical quantum states, including the single-magnon state and the superposition of single-magnon state and vacuum (zero magnon) state. Moreover, we confirm the deterministic generation of these nonclassical states by Wigner tomography. Our experiment offers the first reported deterministic generation of the nonclassical quantum states in a macroscopic spin system and paves a way to explore its promising applications in quantum engineering.
We propose a protocol for generating magnonic squeezed states (MSS) and their superpositions (SMSS) in a hybrid system comprising a superconducting flux qubit magnetically coupled to the Kittel mode of a yttrium iron garnet (YIG) sphere. The flux qubit provides an intrinsic longitudinal interaction with the magnon mode, which, under resonant microwave driving, gives rise to an effective qubit-state-dependent squeezing Hamiltonian. Numerical simulations incorporating realistic dissipation demonstrate that magnon quadrature noise reduction exceeding 8 dB8~\mathrm{dB}8 dB is achievable with experimentally accessible parameters.~By preparing the qubit in a superposition state followed by projective measurement, we further obtain symmetric and antisymmetric superpositions of orthogonally squeezed magnon states exhibiting clear phase-space interference fringes.~We discuss how the fourfold rotational symmetry of these states supports a bosonic logical encoding with potential for protecting against dominant error channels in magnonic platforms.
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 experimentally demonstrate magnon Kerr effect in a cavity quantum electrodynamics (QED) system, where magnons in a small yttrium iron garnet (YIG) sphere are strongly but dispersively coupled to the photons in a three-dimensional cavity. When the YIG sphere is pumped to generate considerable magnons, the Kerr effect yields a perceptible shift of the cavity central frequency and more appreciable shifts of the magnon modes. We derive an analytical relation between the magnon frequency shift and the drive power for the uniformly magnetized YIG sphere and find that it agrees very well with the experimental results of the Kittel mode. Our study paves the way to explore nonlinear effects in the cavity QED system with magnons.