Rydberg quantum optics allows to create strong optical nonlinearities at the level of individual photons by mapping the strong dipolar interactions between collective Rydberg excitations onto optical photons. The interactions lead to a blockade effect such that an optical medium smaller than the blockaded volume only supports a single excitation which is collectively shared amongst all blockaded atoms forming a ‘Rydberg superatom’. Thanks to the collective nature of the excitation, the superatom effectively represents a single emitter with a strongly enhanced coupling to few-photon probe fields with directional emission into the initial probe mode .
This makes Rydberg superatoms an ideal platform to study the interaction of individual two-level emitters with quantised light fields. The interaction leads for example to the emergence of two- and three-photon correlations in the transmitted light, while exchange interactions between the constituent atoms within a superatom lead to non-trivial decay dynamics of the collective state .
When combined with controlled dephasing into dark, collectively excited states, we exploit the strong photon-emitter coupling to subtract exact photon numbers from incoming light fields providing a means to precisely manipulate their quantum state . To this end, we cascade multiple superatoms in 1D chain along mode of the probe field. In the regime of low dephasing, such a cascaded quantum system of multiple superatoms also offers the prospect to observe photon-mediated interactions and entanglement along the probe mode which effectively forms a freespace ‘waveguide’.
We also provide a brief outlook on a new cryogenic experimental platform in which we plan to study hybrid quantum systems of Rydberg atoms combined with e.g. electromechanical oscillators or integrated photonic and microwave circuits.
 A. Paris-Mandoki, C. Braun, J. Kumlin, C. Tresp, I. Mirgorodskiy, F. Christaller, H. P. Büchler, and S. Hofferberth, Phys. Rev. X 7, 041010 (2017).
 N. Stiesdal, H. Busche, J. Kumlin, K. Kleinbeck, H. P. Büchler and S. Hofferberth, Phys. Rev. Research 2, 043339 (2020).
 N. Stiesdal, H. Busche, K. Kleinbeck, J. Kumlin, M. G. Hansen, H. P. Büchler and S. Hofferberth, Nat. Commun. 12, 4328 (2021).
|Presenter name||Hannes Busche|
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