Impact of long-range interactions on phase transitions in spin-boson models

这个项目的目标是研究在所有自旋之间的集体相互作用的作用下，同时与相邻自旋之间的远程相互作用作用的自旋系统的集体行为。为了进行这项研究，我们将在实验上实现Dicke-Ising自旋玻色子模型。自旋态是由冷原子基态的塞曼子能级实现的。集体相互作用是通过在光学腔内定位原子来实现的。原子将被横向光泵浦到腔轴，并被集体驱动进入Dicke相变。同时，通过将其中一个自旋态耦合到具有失谐的里德堡态(里德堡修饰法)，产生了长程相互作用。从而实现了微米量级的长程自旋间的有效伊辛相互作用。我们将首先研究弱长程相互作用对原子集体动力学的影响，分别研究它们对Dicke相图的影响。第二步将解决伊辛相互作用具有可比性并与Dicke模型的耦合强度竞争的体制，并寻找新的相和相变。实验工作将通过与一个理论项目的合作，在“失去平衡的长程相互作用量子自旋系统：实验、理论和数学(QUSP)”研究单元内得到支持。这将从理论上研究Dicke-Ising模型，并对预期相图和相变时的普遍行为做出预测。它还将研究基于腔镜传输光子的耗散效应。这项研究的结果将导致可以在实验中使用的工具，以便利用腔外耦合的光子来识别和表征动力学相和相变。

The goal of this project is to study the collective behavior of a spin system under the action of collective interactions between all spins, simultaneously acting with long-range interactions between neighbouring spins. In order to carry out this study, we will experimentally implement a Dicke-Ising spin-boson model. Spin states are realized by Zeeman sublevels of the ground state of cold Rubidium atoms. Collective interactions are mediated by positioning the atoms inside an optical cavity. The atoms will be optically pumped transversally to the cavity axis and collectively driven into the Dicke phase transition. At the same time, long-range interactions are generated by coupling one of the spin states to a Rydberg state with detuning (Rydberg dressing). Thus, an effective Ising interaction is realized between the spins, which is long-range on the order of micrometers. We will first study the influence of weak, long-range interactions on the collective dynamics of the atoms, respectively their influence on the Dicke phase diagram. A second step will address the regime, where Ising interactions are comparable and compete with the coupling strength of the Dicke model, and search for new phases and phase transitions. Experimental work will be supported within the research unit "Long-range interacting QUantum SPin systems out of equilibrium: Experiment, Theory and Mathematics (QUSP)" by a collaboration with a theoretical project. This will investigate the Dicke-Ising model theoretically and make predictions on the expected phase diagram and on universal behavior at the phase transition. It will also study dissipative effects based on cavity mirror transmission of photons. The results of this study will lead to tools that can be used within the experiment in order to identify and characterize dynamical phases and phase transitions using photons that are coupled out of the cavity.