Quantum Optics Seminar by Jan Kumlin and Kevin Kleinbeck
In the first part of the talk, we present the exact input-output formalism to describe the phenomenon of collective Rabi oscillations in a single Rydberg two-level superatom coupled to a photon field . The photonic mode then defines an effective one-dimensional system, while the large size of the atomic cloud provides a chiral coupling. Extending the theory to describe several atoms coupled to a one-dimensional waveguide also provides a first approach to investigate coherent internal dynamics of the atomic cloud by the exchange of virtual photons .
In the second part of this talk, we discuss the experimental observation of nontrivial three-photon correlations imprinted onto initially uncorrelated photons through the interaction with the single Rydberg superatom . Using the quantum regression theorem, we are able to calculate the correlation functions within the theory discussed in the first part of the talk. Furthermore, we present an idealized but exactly solvable model of a single two-level system coupled to a photonic mode, which allows for an interpretation in terms of bound states and scattering states and serves as a starting point to investigate the validity of the quantum regression theorem in our setup.
 A. Paris-Mandoki, C. Braun, J. Kumlin, C. Tresp, I. Mirgorodskiy, F. Christaller, H. P. Buchler, and S. Hofferberth, Phys. Rev. X 7, 41010 (2017)
 N. Stiesdal, J. Kumlin, K. Kleinbeck, P. Lunt, C. Braun, A. Paris-Mandoki, C. Tresp, H. P. Büchler, and S. Hofferberth, Phys. Rev. Lett. 121, 103601 (2018)
 J. Kumlin, S. Hofferberth, and H. P. Büchler, Phys. Rev. Lett. 121, 013601 (2018)