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Project 3: Local and single atom resolved study of non-linear excitation dynamics and dissipation in off-resonantly driven Rydberg gases


Non-equilibrium phenomena are the main objective of this project. The fact that our everyday world is full of dynamical processes rather than being in static thermal equilibrium highlights the importance of a thorough understanding of those processes. However, detailed understanding of out-of-equilibrium systems still poses an outstanding challenge.

Within this project, we aim to implement the “directed percolation” (DP) model with ultracold Rydberg atoms held in an optical lattice. For the theoretical study of non-equilibrium dynamics, this model has a similar significance as the Ising model for equilibrium statistical mechanics, providing a simple reference model to study generic features of non-equilibrium phenomena. The practical relevance stems for example from the fact that DP provides a simplifying model for the description of the spreading of a disease in a population. Interestingly, in analogy to equilibrium systems, a phase transition has been predicted to occur in DP between a state of growing infection and an absorbing state without proliferation of the disease. Despite their obvious practical importance, detailed experimental studies of non-equilibrium phase transitions and their critical behavior are rare and so far limited to classical models.

Recently, it was predicted that the DP model can be implemented utilizing conditional facilitation processes, which can be realized in an ultracold gas of Rydberg atoms via off-resonant excitation to the Rydberg manifold. For this, we plan to use direct single photon transition at 297nm from the ground state to the excited Rydberg state, providing controlled coupling to Rydberg states with p-state character. Adding a second laser at 702nm will enable to engineer the dissipative rate present in the system by controlled coupling low-lying, fast-decaying states. In the picture of the DP model describing the spreading of a disease, these two ingredients realize the infection by an already infected person and the curing of an ill person with variable rates respectively.

The system will be probed locally using a high resolution objective in combination with fluorescence imaging, which provides the full information on the spatial position of each atom, and hence enables the local study of the dynamics present in the DP model. Exemplary single shots of a driven Rydberg gases are showing in Fig. 1, highlighting the presence of the facilitation and demonstrating the feasibility of this detection method. Using the p-state transition has the additional advantage that very high coupling rates in the MHz regime can be reached, which, in combination with dissipation engineering, opens the path to studying the dynamics of the system after long evolution times and entering the quantum realm.

Figure 1: Distribution of atoms in an optical lattice. The lines of missing atoms demonstrate the presence of facilitation in the system, a necessary ingredient for the realization of directed percolation.

The developed technology will enable the study of DP both in the classical and in the quantum regime on a microscopic level. This will include a study of the critical regime around the expected non-equilibrium phase transition, providing an experimental reference for developing theories of non-equilibrium quantum systems.


Prof. Dr. Immanuel Bloch, Max-Planck-Institut für Quantenoptik