We demonstrate genuine tripartite strong coupling in a solid-state hybrid quantum system comprising a superconducting transmon qubit, a fixed-frequency coplanar-waveguide resonator, and an ensemble of NV− centers in diamond. Frequency-domain spectroscopy reveals a characteristic three-mode avoided crossing, indicating that single excitations are coherently shared across all three subsystems. At higher probe powers, we observe nonlinear features including multiphoton transitions and signatures of transmon-14N nuclear-spin interactions, highlighting the accessibility of higher-excitation manifolds in this architecture. These results establish a new regime of hybrid cavity QED that integrates superconducting and spin degrees of freedom, providing a platform for exploring complex multicomponent dynamics and developing hybrid quantum interfaces.
@article{arxiv.2512.13129,
title = {Genuine Tripartite Strong Coupling in a Superconducting-Spin Hybrid Quantum System},
author = {Yingqiu Mao and Han-Yu Ren and Zi-Yi Liu and Yi-Zheng Zhen and Tao Rong and Tao Jiang and Zhuo Chen and Zhe-Heng Yuan and Wen-Hua Qin and Xiaoran Zhang and Xiaobing Liu and Ming Gong and Kae Nemoto and William J. Munro and Johannes Majer},
journal= {arXiv preprint arXiv:2512.13129},
year = {2025}
}