Single Atomic Impurities in Engineered Baths
January 30th, 2020 ARTUR WIDERA Technische Universität Kaiserslautern

Experimental control over individual atoms has paved the way to realize, study and control a paradigm of open quantum systems: a single atom immersed in an ultracold bath. I will present our experimental progress in immersing single neutral Cesium impurities into an ultracold Rb gas. Employing the powerful toolbox of cold atom systems, we have studied both, motional and spin dynamics of single impurities coupled to different baths. Our studies include the nonergodic diffusion of single atoms in engineered light fields as well as in ultracold gases, shedding light on Brownian motion in extreme scenarios. Moreover, unleashing the spin-degree of freedom, we investigate the spin-exchange dynamics of individual impurities in a quantum gas at ultralow energies. Employing such a spin-exchange, we utilize single atoms as quantum probes, mapping information of the Rb bath onto the quantum-spin distribution of the impurity. Surprisingly, we find that working in the regime of nonequilibrium spin dynamic, the sensitivity of the probe beats the fundamental Cramér-Rao bound of equilibrium quantum mechanics by one order of magnitude. Finally, I will discuss the prospect of using impurities as single-atom machines, where our high level of microscopic control over interaction mechanisms allows blocking specifically those collisions which establish thermal equilibrium. Thus, we can run a single-atom engine which is not restricted anymore by the limits of thermal distributions, but which can turn over an order of magnitude more energy as compared to the thermal counterpart.

Seminar, January 30, 2020, 15:30. ICFO’s Seminar Room

Hosted by Prof. Maciej Lewenstein