Quantum Magnonics: Quantum States Generation and Applications

Quantum magnonics explores the quantum properties of magnons—collective excitations of spins in ferromagnetic materials like yttrium iron garnet (YIG). Over the last decade, the field has evolved from basic material characterization to the development of hybrid quantum systems. By coupling magnons to microwave photons, optical photons, superconducting qubits, and phonons, researchers can now manipulate these collective spin states with high precision. The central requirement for these applications is the strong coupling regime, where the rate of energy exchange between the magnon and the coupled system exceeds their respective dissipation rates.

The most mature platform in this field is the cavity electromagnonic system, where a YIG sphere is placed inside a microwave cavity. This setup allows for the coherent control of magnons and the generation of quantum states. By introducing nonlinearities—often through magnetostrictive interactions or coupling to superconducting qubits—researchers can move beyond simple energy exchange to create non-classical states. For instance, magnon–photon entanglement can be generated by exploiting magnetostrictive coupling to mechanical modes or through dissipative coupling in parity-time symmetric systems. These states are not only of fundamental interest for studying the quantum-to-classical transition in macroscopic objects but also serve as resources for quantum technologies.

The ability to generate and manipulate magnonic quantum states opens doors to several high-impact applications. In quantum sensing, squeezed magnon states can enhance the sensitivity of detectors, potentially aiding in the search for dark matter axions. In quantum information science, the hybrid nature of these systems allows for microwave-to-optical transduction, which is essential for connecting superconducting quantum processors via long-distance optical fiber networks. As the field matures, the focus is shifting toward increasing the coherence times of these systems and integrating them into larger, multi-node quantum architectures.