Non-classical 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 {\it in situ} via the Autler-Townes effect, we manipulate this single magnon to generate its non-classical quantum states, including the single-magnon state and the superposition state of a single magnon and vacuum. Moreover, we confirm the deterministic generation of these non-classical states by Wigner tomography. Our experiment offers the first reported deterministic generation of the non-classical quantum states in a macroscopic spin system and paves a way to explore its promising applications in quantum engineering.
@article{arxiv.2211.06644,
title = {Quantum control of a single magnon in a macroscopic spin system},
author = {Da Xu and Xu-Ke Gu and He-Kang Li and Yuan-Chao Weng and Yi-Pu Wang and Jie Li and H. Wang and Shi-Yao Zhu and J. Q. You},
journal= {arXiv preprint arXiv:2211.06644},
year = {2023}
}