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Q: Fachverband Quantenoptik und Photonik

Q 58: Ultrakalte Atome (Einzelne Atome)

Q 58.1: Group Report

Friday, March 14, 2008, 11:00–11:30, 3B

Quantum nonlinearity with one atom dressed by two photons — •Ingrid Schuster, Alexander Kubanek, Andreas Fuhrmanek, Thomas Puppe, Pepijn Pinkse, Karim Murr, and Gerhard Rempe — Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching

The strong-coupling regime of cavity QED has proven to be a rich pond of optical phenomena at the level of single atoms and photons. We experimentally demonstrate that such a system exhibits a nonlinear intensity response when a single atom is made to interact not with one, but with two photons at the same time. This nonlinearity is explained by quantum mechanics and is expected to vanish in the limit of many intracavity atoms. It originates from the energy-level structure of the system, which consists of a ladder of doublets with anharmonic level splitting. The first doublet is visible in low-intensity spectroscopy, where it leads to the well-known vacuum-Rabi or normal-mode splitting. For stronger driving, we find a resonance stemming from excitation of the second doublet, at a frequency which is distinct from the normal modes because of the anharmonicity of the energy level spectrum. Since we access the resonance by driving a two-photon transition, we see a mainly quadratic response with respect to the probe intensity. Our experiment opens up new avenues for the controlled generation of multi-photon states.