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Optics Express

Steady-state magnon entanglement and backaction-evading of a weak magnetic signal via two-tone modulated cavity electromagnonics

Nianqi Hu, Huatang Tan

Published Sep 4, 2024• 2 citations
Publisher

Abstract

Cavity electromagnonics explore the coupling between microwave cavity fields and magnons in micromagnets. This field has emerged as a promising platform for probing fundamental aspects of quantum mechanics and advancing quantum technologies. This paper investigates a scheme involving two-tone frequency modulation to engineer simultaneous magnon-photon two-mode squeezing and beam-splitter-like interactions. We demonstrate that this scheme enables the direct generation of macroscopic magnonic squeezed and entangled states. Moreover, it facilitates ultra-sensitive magnon-based magnetic field sensing through quantum non-demolition (QND) interactions between magnons and photons. The present scheme provides promising opportunities for generating macroscopic nonclassical quantum states in solid magnetic materials and developing spintronics-related quantum devices.

DOI
10.1364/oe.536838

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Cavity electromagnonics explore the coupling between microwave cavity fields and magnons in micromagnets. This field has emerged as a promising platform for probing fundamental aspects of quantum mechanics and advancing quantum technologies. This paper investigates a scheme involving two-tone frequency modulation to engineer simultaneous magnon-photon two-mode squeezing and beam-splitter-like interactions. We demonstrate that this scheme enables the direct generation of macroscopic magnonic squeezed and entangled states. Moreover, it facilitates ultra-sensitive magnon-based magnetic field sensing through quantum non-demolition (QND) interactions between magnons and photons. The present scheme provides promising opportunities for generating macroscopic nonclassical quantum states in solid magnetic materials and developing spintronics-related quantum devices.
Cavity electromagnonics has increasingly emerged as a new platform for the fundamental study of quantum mechanics and quantum technologies. Since the coupling between the microwave field and magnon Kittle modes in current experiments is much weaker than their resonant frequencies, the anti-rotating terms in magnon-microwave-photon interaction can be neglected and only the beam-splitter-like part takes effect. In this situation, the direct generation of magnonic nonclassical states is impossible, unless other subsystems e.g. phonons, squeezed photons or superconducting qubits are incorporated. In this paper, we consider two-tone modulated cavity electromagnonics to keep the nontrivial anti-rotating terms and obtain tunable phase factors, resulting in an effective Hamiltonian exactly the same as that of generic linearized cavity optomechanics. This can therefore be exploited to directly prepare macroscopic magnonic quantum states, as detailedly exemplified by the generation of steady and strongly squeezed and entangled states, realize ultra-sensitive magnon-based sensing by engineering backaction-evading interaction of magnons and photons, and develop spintronics-related quantum information processing devices.
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.
Abstract Generating and manipulating magnon quantum states for quantum information processing is a central topic in quantum magnonics. The conventional strategy amplifies the nonlinear interaction among magnons to manifest their quantum correlations at cryogenic temperatures, which is challenging for magnets with vanishingly small nonlinearities. Here we propose an unconventional approach to prepare entangled states of two distant magnon modes by applying a two-tone Floquet field to each magnet inside a microwave cavity. The Floquet driving can effectively generate parametric interaction between magnons and photons, and thus opens an indirect entanglement channel between the two magnon modes mediated by cavity photons. By optimizing the relative ratio of the magnon–photon coupling and the detuning between the magnon modes, the two magnon modes can reach a stationary and robust entanglement, of which the strength is enhanced compared with entanglement generated via magnetic nonlinearities. Furthermore, one-way steering between the two magnets is realized by engineering unequal damping rates of the two magnets while the steering asymmetry can be efficiently modulated by tuning the coupling strength of magnons and cavity photons. The essential physics of our findings universally applies to a wide class of magnets with small nonlinearities and may find promising applications in engineering robust magnon quantum states for quantum information science.
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.
Cavity magnonics, owing to its strong magnon-photon coupling and excellent tunability, has attracted significant interest in quantum information science. However, achieving strong and robust macroscopic entanglement remains a long-standing challenge due to the inherently linear nature of the beam-splitter interaction. Here, we propose an experimentally feasible scheme to generate and enhance macroscopic entanglement between two remote magnon modes by injecting squeezed vacuum fields (SVFs) into coupled microwave cavities. We demonstrate that even a single SVF applied to one cavity can induce steady magnon-magnon entanglement, while applying two SVFs (the double-squeezed configuration) enables selective activation of two independent entanglement channels associated with the cavity supermodes. Remarkably, quantum interference between the two SVFs allows for phase-controlled enhancement of entanglement, resulting in significantly improved robustness against cavity dissipation and thermal noise. Under realistic parameters, the survival temperature of quantum entanglement increases from approximately 260260260 mK to 450450450 mK. Our results establish a versatile and controllable approach to generating and enhancing quantum entanglement through quantum interference between squeezed vacuum fields.
We propose a scheme to generate entanglement between two cavity modes and squeeze magnon mode in a magnon-cavity QED system, where the two microwave cavity modes are coupled with a massive yttrium iron garnet (YIG) sphere through magnetic dipole interaction. The nonlinearity used in our system originates from a squeezed driving via parametric down-conversion process, which is the reason to cause entanglement and squeezing. By using the mean field approximation and employing experimentally feasible parameters, we demonstrate that the system shows zero entanglement and squeezing without squeezed driving. Meanwhile, our QED system denotes that the entanglement between squeezed cavity mode and magnon mode can be transferred to the other cavity mode and magnon mode via magnon-cavity coupling interaction, and then the two cavity modes get entangled. A genuinely tripartite entangled state is formed. We also show that magnon mode can be prepared in a squeezed state via magnon-cavity beam-splitter interaction, which is as a result of the squeezed field. Moreover, we show that it is a good way to enhance entanglement and squeezing by increasing the nonlinear gain coefficient of squeezed driving. Our results denote that magnon-cavity QED system is a powerful platform for studying macroscopic quantum phenomena, which illustrates a new method to photon-photon entanglement and magnon squeezing.