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arXiv:2604.02924

Generation of magnonic squeezed state and its superposition in a hybrid qubit-magnon system

Gang Liu, Junpeng Liu, Feng Qiao, Rong-Can Yang

quant-phSubmitted Apr 3, 2026• Announced Apr 6, 2026• 0 citations• Revised Apr 15, 2026 (v3)
v1 · Apr 3, 2026v2 · Apr 11, 2026v3 · Apr 15, 2026
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Abstract

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 $8~\mathrm{dB}$ 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.

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Physical Review A•Aug 23, 2024•4 citations
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.
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.
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.
We theoretically propose a magnon-based superconducting qubit hybrid system containing two ferromagnetic yttrium iron garnets (YIGs) and one superconducting qubit, demonstrating that this hybrid quantum system is feasible in achieving the unconventional two-mode magnon blockade and generating the quantum correlated magnon pairs. Through the virtual-photon excitation mediated by the same cavity mode, the effective couplings can be established not only between the Kittel modes and the qubit, but also between the two Kittel modes. We characterize the magnon blockade by utilizing the equal-time second-order correlation functions and impose a constraint on the correlations between the two Kittel modes by introducing the Cauchy-Schwarz inequality (CSI). In the weak qubit-magnon coupling regime, our results indicate the following: (i) Under the scenario of the resonance couplings, the ratio of driving strengths and the ratio of coupling strengths between the two Kittel modes and the cavity mode can be employed to control and regulate the magnon blockade and the violation of the CSI. Not only the two Kittel modes can achieve the unconventional magnon antibunching effects simultaneously, but also the correlations between them violate the classical CSI. It is important to note that when the degrees of both the antibunching effects for the two Kittel modes and the anticorrelation between them reach their highest levels simultaneously, the correlations happen not to violate the CSI. But our proposal offers a feasible route for preparing a high-quality single-magnon source. (ii) Under the scenario of the out-of-resonance couplings, by adjusting the frequency detunings between the first Kittel mode and the second Kittel mode as well as the qubit, the quantum correlated two-mode magnon pairs can be obtained. (iii) Finally, it is found that the magnon antibunching effect of the second Kittel mode is robust against the dissipation ratio between the two Kittel modes. These results illustrate how to optimally choose the parameters to realize nonclassical magnon pair generation and CSI violation. The hybrid YIG quantum system we propose here holds the potential in the development of efficient microwave single-magnon sources and quantum magnon-magnon pairs required in future quantum information processing tasks.
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.
Bosonic quantum error correction encodes a logical qubit in an oscillator, avoiding the hardware overhead of large qubit arrays. Among such encodings, Gottesman-Kitaev-Preskill (GKP) states are paticularly powerful because their phase-space grid structure protects against small displacement errors simultaneously in both conjugate quadratures. Here we provide the first protocol for preparing magnonic GKP states, which involves an ellipsoidal magnetic crystal effectively coupled to a superconducting qubit via a microwave cavity. The geometric anisotropy intrinsically squeezes the magnon mode, while the cavity-mediated qubit control realizes an effective conditional-displacement interaction. We show that two rounds of a conditional-displacement interaction and a qubit projective measurement yield three- and four-component magnonic GKP-like states. We also show how to realize single logical qubit gate operations, such as Pauli, Hadamard and phase gates, completing the logical Pauli basis of the approximate GKP code. Our results establish hybrid magnon-qubit systems as a promising platform for preparing bosonic code states, with applications in magnonic fault-tolerant quantum computation and quantum sensing.
The implementation of quantum network made up of multiple nodes and channels needs to take advantage of hybrid quantum systems. So far, in the hybrid ferromagnet-superconductor quantum system, the establishment of the remote effective interactions based on the virtual photons exchange mediated by the microwave cavity mode has been experimentally confirmed, providing a physical basis for the implementation of the remote signal transfer from one node to another. In this work, we put forward a magnon-based hybrid quantum system consisting of two macroscopic spin subsystems [i.e., millimeter-diameter ferromagnetic yttrium-iron-garnet (YIG) spheres] and one transmon-type superconducting qubit, and show that the mechanism of the cavity-mediated remote magnon-mode intertalk is feasible for achieving microwave signal transfer, simultaneously accompanied by a transition from Poissonian to sub-Poissonian statistics. We find that by tuning the typical system parameters properly, even if there is a mismatch in magnon-mode frequencies or dissipation rates between the two YIG spheres, the microwave information transfer from one YIG sphere to another is still robust, where the signal output through another YIG sphere exhibits pronounced antibunching. In addition, the proposed hybrid quantum system possesses a robustness window against the dissipation rates of both the qubit and the two Kittel modes. The analytical calculations and numerical simulations are conducted under experimentally accessible conditions, and the consistency of the results attained by these two methods makes our research more credible. Physically, we notice that two conversion channels are opened. One channel comes from the linear coupling. The other is based on the nonlinear interaction, which also is the underlying mechanism responsible for nonclassical sub-Poissonian signal output.