标题： 泽曼极化子作为探测凝聚态中迪克物理的平台 显示英文标题

标题： Zeeman polaritons as a platform for probing Dicke physics in condensed matter

摘要： 一个由两能级原子组成的系综与量子化电磁场的相互作用，由迪克哈密顿量描述，是量子光学中广泛研究的问题。 然而，实验上探索凝聚态中类似物理现象通常采用可描述为简谐振荡器的玻色物质模式（例如声子、磁子和等离子体），即无限级距的等间距能级。 在这里，我们研究了相干光模与钆$_3$钇$_5$氧$_{12}$中参数磁自旋系综之间的超强耦合，这是一个有限多能级系统。 钆$^{3+}$离子的电子顺磁共振通过磁场调谐与法布里-珀罗腔模共振，导致自旋-光子混合态或塞曼极化子的形成。 我们观察到，通过真空瑞利分裂测量的光-物质耦合强度随着温度的升高而减小，这可以通过低能态和高能态之间随温度变化的粒子数差来解释，这是有限能级系统的特征。 这一发现表明，自旋-玻色系统比玻色-玻色系统更符合迪克模型，并在追求超强耦合光-物质杂化体系预测现象的实验实现方面具有优势。 显示英文摘要

摘要： The interaction of an ensemble of two-level atoms and a quantized electromagnetic field, described by the Dicke Hamiltonian, is an extensively studied problem in quantum optics. However, experimental efforts to explore similar physics in condensed matter typically employ bosonic matter modes (e.g., phonons, magnons, and plasmons) that are describable as simple harmonic oscillators, i.e., an infinite ladder of equally spaced energy levels. Here, we examine ultrastrong coupling between a coherent light mode and an ensemble of paramagnetic spins, a finite-multilevel system, in Gd$_3$Ga$_5$O$_{12}$. The electron paramagnetic resonance of Gd$^{3+}$ ions is tuned by a magnetic field into resonance with a Fabry--P\'erot cavity mode, resulting in the formation of spin--photon hybrid states, or Zeeman polaritons. We observe that the light--matter coupling strength, measured through the vacuum Rabi splitting, decreases with increasing temperature, which can be explained by the temperature-dependent population difference between the lower and higher-energy states, a trait of a finite-level system. This finding demonstrates that a spin--boson system is more compatible with the Dicke model and has advantages over boson--boson systems for pursuing experimental realizations of phenomena predicted for ultrastrongly coupled light--matter hybrids.