The experimental advance on light–matter interaction into strong couplings has invalidated the Jaynes–Cummings model and brought the quantum Rabi model (QRM) to more relevance. The QRM only involves linear coupling via a single -photon process (SPP), while the nonlinear two -photon process (TPP) is weaker and conventionally neglected. However, we find a contrary trend that enhancing the linear coupling might not suppress the nonlinear effect more but backfire to trigger some collapse of linear characters. Indeed, in strong SPP couplings a tiny strength of the TPP may dramatically change properties of the system, like a symmetry spontaneous breaking. By extracting the ground-state phase diagram including both a SPP and TPP, we find the TPP in low frequency limit induces a quantum phase transition with continuity–discontinuity double faces, which split into two distinct transitions at finite frequencies and yields a triple point. Our analysis unveils a subtle SPP–TPP e...

中文翻译：

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非线性量子拉比模型中的量子相变和自发对称性破裂

关于光-物质相互作用成强耦合的实验进展使Jaynes-Cummings模型无效，并使量子Rabi模型（QRM）更具相关性。QRM仅涉及通过单光子过程（SPP）进行的线性耦合，而非线性两光子过程（TPP）则较弱并且通常被忽略。但是，我们发现相反的趋势，即增强线性耦合可能不会更多地抑制非线性效应，反而会触发线性字符的崩溃。实际上，在强SPP耦合中，TPP的微小强度可能会极大地改变系统的属性，例如对称的自发破裂。通过提取同时包含SPP和TPP的基态相位图，我们发现TPP在低频范围内会诱发具有连续性-不连续性双面的量子相变，它在有限的频率上分为两个不同的跃迁，并产生一个三点。我们的分析揭示了微妙的SPP–TPP e ...