Optics Seminar

When an impurity is immersed into an environment, it changes itsproperties due to its interactions with the surrounding medium. Theimpurity is dressed by many-body excitations and forms aquasiparticle, the polaron. Depending on the character of theenvironment and the form of interactions, different types of polaronsare created. In this talk, I will review recent experimental andtheoretical progress on studying the many-body physics of polarons inultracold atomic systems [1], and discuss related polaronic phenomenaencountered in two-dimensional semiconductors [2] and the study ofrotating molecules in superfluid Helium [3]. I will then putparticular focus on impurities interacting with bosonic quantum gasesand discuss the recent progress on the theoretical description ofRydberg excitations coupled to Bose-Einstein condensates. In suchsystems the interaction between the Rydberg atom and the Bose gas ismediated by the Rydberg electron. This gives rise to a new polaronicdressing mechanisms, where instead of collective excitations,molecules of gigantic size dress the Rydberg impurity. We develop afunctional determinant approach [4] to describe the dynamics of suchRydberg systems which incorporates atomic and many-body theory. Usingthis approach we predict the appearance of a superpolaronic statewhich has recently been observed in experiments [5,6]. References:[1] R. Schmidt, M. Knap, D. A. Ivanov, J.-S. You, M. Cetina, and E.Demler, Rep. Prog. Phys. 81, 024401 (2018).[2] M. Sidler et al., Nature Physics 13, 255 (2017)[3] R. Schmidt, and M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015);[4] R. Schmidt, H. Sadeghpour, and E. Demler, Phys. Rev. Lett. 116,105302 (2016).[5] F. Camargo et al., Phys. Rev. Lett. 120, 083401 (2018).[6] R. Schmidt et al., Phys. Rev. A 97, 022707 (2018).