SPICE Workshop on Quantum Functionalities of Nanomagnets, June 17th - 19th 2025
María José Martínez Pérez
Cavity Quantum Electrodynamics (C-QED) is a powerful tool for manipulating and interrogating qubits or engineering matter polaritons. However, cavity photons in superconducting circuits impose restrictions on the maximum coupling strengths, thereby constraining the regimes and physical phenomena that can be explored within C-QED platforms. Beyond photons, the solid state offers many other quantized bosonic excitations. Among these, magnons—the quanta of spin waves in magnetic solids—stand out. The rich physics of light-matter hybrids is, in principle, transferable to magnon-matter systems, which present notable advantages, including reduced cavity size and enhanced coupling strengths.
In this work, we report the first experimental observation of strong magnon-spin coupling. To achieve this, we utilize a layered van der Waals antiferromagnet, CrSBr, as the magnonic cavity, and a paramagnetic ion crystal, GdW₁₀, as the solid-state spin ensemble. Using microwave absorption spectroscopy at millikelvin temperatures, we detect an avoided crossing that vanishes at high power. Our theoretical framework reveals that this power-dependent behavior arises from saturation, allowing us to quantify the effective number of spins hybridized with the magnon modes. These findings pave the way for the use of CrSBr and similar layered materials as magnonic platforms in hybrid quantum systems, offering potential applications in both fundamental research and quantum devices.