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Magnomechanical rotational Schrödinger’s cat

A. Kani, Mohamed Hatifi, Jason Twamley

Published Oct 9, 2025• 1 citation
Publisher

Abstract

We propose a novel method to generate a rotational Schrödinger’s cat state made of a superposition of coherent angular oscillations (librations) of a levitated magnonic nanoparticle. By taking advantage of the magnetocrystalline anisotropy, we achieve quadratic magnon-rotational coupling. This coupling is particularly significant for small nanoscale objects. By driving the magnon with a bichromatic microwave field, we induce nonlinear rotational dissipation and parametrically excite the libration motion. This enables an efficient generation of a rotational cat state, which, under high vacuum conditions, can persist for several minutes. Our approach provides a robust and novel platform for exploring quantum superposition of rotation, which has potential applications in testing collapse models and gravitational effects on rotating quantum objects.

DOI
10.1063/5.0280923

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We propose a novel method to generate a rotational Schrödinger’s cat state made of a superposition of coherent angular oscillations (librations) of a levitated magnonic nanoparticle. By taking advantage of the magnetocrystalline anisotropy, we achieve quadratic magnon-rotational coupling. This coupling is particularly significant for small nanoscale objects. By driving the magnon with a bichromatic microwave field, we induce nonlinear rotational dissipation and parametrically excite the libration motion. This enables an efficient generation of a rotational cat state, which, under high vacuum conditions, can persist for several minutes. Our approach provides a robust and novel platform for exploring quantum superposition of rotation, which has potential applications in testing collapse models and gravitational effects on rotating quantum objects.
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We propose an efficient method for dissipative generation of magnonic cat states in a cavity-magnon-qubit hybrid system by exploiting a two-magnon driving and dissipation mechanism. When both the magnon and qubit are driven, a coherent nonlinear two-magnon interaction is induced, wherein the qubit and the magnon mode exchange energy through magnon pairs. The dissipation of the qubit is exploited to steer the magnon mode into a quantum superposition of distinct coherent states, where the magnon mode evolves into either an even or odd cat state, depending on the parity of the magnon initial state. For the case where the magnon initial state is a superposition state, e.g., of $|0\ensuremath{\rangle}$ and $|1\ensuremath{\rangle}$, the magnon mode can evolve into a weighted mixture of the even and odd cat states. We also find that magnon squeezed states may emerge during the short-time evolution, showcasing the capability of our mechanism in preparing diverse magnon nonclassical states. Magnonic cat and squeezed states are macroscopic quantum states and have applications in macroscopic quantum studies and quantum sensing, e.g., in the dark-matter search using ferromagnetic axion haloscopes.
Nonlinearities in multimode mechanical systems can give rise to rich dynamical phenomena with great potential for sensing applications and for future quantum experiments. We demonstrate that the coupled center-of-mass and rotational motion of a Meissner-levitated micromagnet offer a promising platform for nonlinear dynamics, combining low dissipation, magnetic tunability, strong intrinsic Duffing nonlinearities, and nonlinear intermodal couplings. We use this tunability to demonstrate the generation of a mechanical frequency comb in the micromagnet dynamics, realized by parametric excitation of two translational modes followed by cascaded nonlinear frequency mixing, which produces a phononic comb with tunable spacing. At large amplitudes, nonlinear coupling to a low-frequency librational mode of the magnet leads to parametric excitation and phase locking of that mode, generating a dense spectral fine structure at subharmonics of the drive. These results establish levitated micromagnets as a platform for nonlinear multimode mechanics, with potential applications in precision sensing and quantum-limited metrology.
The ability to prepare a macroscopic mechanical resonator into a quantum superposition state is an outstanding goal of cavity optomechanics. Here, we propose a technique to generate cat states of motion using the intrinsic nonlinearity of a dispersive optomechanical interaction. By applying a bichromatic drive to an optomechanical cavity, our protocol enhances the inherent second-order processes of the system, inducing the requisite two-phonon dissipation. We show that this nonlinear sideband cooling technique can dissipatively engineer a mechanical resonator into a cat state, which we verify using the full Hamiltonian and an adiabatically reduced model. While the fidelity of the cat state is maximized in the single-photon, strong-coupling regime, we demonstrate that Wigner negativity persists even for weak coupling. Finally, we show that our cat state generation protocol is robust to significant thermal decoherence of the mechanical mode, indicating that such a procedure may be feasible for near-term experimental systems.
Abstract Controlling the motion of nanoscale objects at the quantum limit promises opportunities to test fundamental quantum physics and advances in quantum sensing. Rotational motion is of particular interest, as its nonlinear dynamics in a compact, closed configuration space provides access to phenomena such as rotational interferometry, tunnelling between angular configurations and quantum-enhanced torque sensing. A key requirement for such experiments is the capability to trap nanorotors and cool their orientation close to the two-dimensional librational quantum ground state. When rotational motion is confined in a harmonic potential, it becomes librational. Here we demonstrate that coherent scattering into a high-finesse cavity enables the ground-state cooling of two orthogonal librational modes of an optically levitated SiO 2 nanoparticle. Using a laser-induced desorption loading technique, we trap and cool several dimers and trimers of silica nanospheres to their respective ground states, all within a single day. The simultaneous cooling of both librational degrees of freedom allows us to align an individual nanorotor with respect to a space-fixed axis with an angular precision better than 20 µrad—close to the quantum-mechanical zero-point fluctuations.
The direct coupling system between a magnon and a superconducting qubit exhibits a special advantage in the quantum information processing [Phys. Rev. Lett. 129, 037205 (2022) ]. In this paper, based on this direct coupling system, the magnonic squeezed Schr\"odinger cat states (MSSCSs) can be generated by the conditional displacement mechanism. Numerical simulation shows that our scheme is robust to the dissipation of the system. In particular, we find that the coherence amplitude of MSSCSs can be enhanced via a squeezed transformation. Our results have potential application in quantum information processing and quantum optics.