HQOC/ITAMP Joint Quantum Sciences Seminar Wednesday, March 9, 2016 4:00 PM, Jefferson 250 Prof. Herwig Ott "Butterfly Molecules in a Bose-Einstein Condensate" This talk will give an overview of recent experiments in my group studying Rydberg excitations and their dynamics in ultra cold quantum gases. We use ionization processes of Rydberg atoms and molecules as a continuous probe of the system. For very small atomic samples with dimensions of a few micrometers, we reach the superatom limit, where only one excitation fits into the sample at the same time. For increasing size, driving strength and for finite detuning we observe the transition to a multiple excitation regime, where small clusters and correlated dynamics appear. For large Bose-Einstein condensates these clusters contain several hundred excitations and lead strongly correlated ion bursts emitted from the system. The discovery of Rydberg molecules offers another route to study degenerate quantum gases. Taking advantage of a single-photon excitation scheme to molecular Rydberg states, we can continuously measure the number of produced molecules. This has allowed us to probe in real time the double occupancy during a sweep over the superfluid to Mott insulator transition. Butterfly molecules are a special type of Rydberg molecules with exceptional properties. Using a single photon excitation to a Rydberg p-state, we observe for the first time these molecules. Due to their large dipole moment in combination with a small bond length, we resolve the rotational and pendular structure in an electric field. This opens new possibilities to study Rydberg molecules with long-range interactions in optical lattices. Dr. Richard Schmidt "A mesoscopic Rydberg impurity in an atomic quantum gas" Impurity problems have been at the forefront of research in condensed matter physics for several decades. In this talk, we show that Rydberg impurity excitations in ultracold quantum gases present a new frontier in impurity research. Here vastly different energy scales compete, signified in deeply bound Rydberg molecules of mesoscopic size. This situation poses a new challenge for theoretical physics and necessitates the confluence of methods ranging from mesoscopic to atomic physics. In our work, we develop a novel many-body theory for the non-equilibrium dynamics of giant impurity excitations Bose gases. Such single Rydberg impurity excitations have recently been observed, and we demonstrate that these observations can be understood from our theoretical approach which incorporates atomic and many-body theory. The crossover from few-body dynamics to quantum many-body collective behavior - manifest in the appearance of a novel superpolaronic state - is elucidated in an unified functional determinant approach, valid at zero and finite temperature. The time-dependent formalism is not restricted to Rydberg systems but can be generally applied to impurities in bosonic and fermionic environments and opens new possibilities to study impurity dynamics in mesoscopic systems. Reference [1] R. Schmidt, H. R. Sadeghpour, and E. Demler, arXiv:1510.09183 (2015). Student Presentation from 4:00-4:10 PM Refreshments Served from 4:00-4:30 PM Guest Presentation from 4:30-6:00 PM -- Clare Ploucha Faculty Assistant to Professors Lukin & Greiner and their labs Department of Physics 17 Oxford St., Lyman 324A Cambridge, MA 02138 P. (617) 496-2544