Prof. Dr. Sebastian Slama
The goal of this project is to study the collective behavior of a spin system under the action of collective interactions between all spins (all-to-all), 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 will be 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 (on the order of micrometers) are generated by coupling one of the spin states to a Rydberg state with large detuning (Rydberg dressing), realizing an effective Ising interaction between the spins. We will first study the influence of weak, long-range interactions on the collective dynamics of the atoms and 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, where we will search for new phases and phase transitions. Experimental work will be supported by a collaboration with a project P2, where the Dicke-Ising model will be investigated theoretically and predictions on the expected phase diagram and on universal behavior at the phase transition will be made. Dissipative effects based on cavity mirror transmission of photons will also be studied, leading 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.