Technische Universitat MunchenMax-Planck-Institut fur QuantenoptikNonlinear spectroscopy of asingle-atom-cavity systemIngrid SchusterVollstandiger Abdruck der von der Fakultat fur Physikder Technischen Universitat Munchenzur Erlangung des akademischen Grades einesDoktors der Naturwissenschaften (Dr. rer. nat.)genehmigten Dissertation.Vorsitzender: Univ.-Prof. Dr. H. FriedrichPrufer der Dissertation: 1. Hon.-Prof. Dr. G. Rempe2. Univ.-Prof. Dr. R. GrossDie Dissertation wurde am 05.06.2008bei der Technischen Universitat Munchen eingereichtund durch die Fakultat fur Physik am 04.07.2008 angenommen.AbstractThe radiative properties of an atom are not only determined by its internal struc-ture, but also by its environment. By modifying the density of the surroundingelectromagnetic modes, the interaction of an atom with light can be increased sig-ni cantly. Such a situation is realized for an atom placed inside a cavity whichsupports only a single mode. If the coupling of the atom to this privileged modeexceeds the interaction of atom and cavity with the external modes, a new systemwith its own characteristic energy structure emerges. This constitutes the ’strong-coupling regime’ of cavity-QED. Here, the energy levels of the system form a ladderof doublets.
Nonlinear spectroscopy of a single-atom-cavity system
Ingrid Schuster
Vollsta¨ndigerAbdruckdervonderFakulta¨tfu¨rPhysik derTechnischenUniversita¨tMu¨nchen zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. nat.)
genehmigten Dissertation.
Vorsitzender:
Pru¨ferderDissertation:
Univ.-Prof. Dr. H. Friedrich
1. Hon.-Prof. Dr. G. Rempe 2. Univ.-Prof. Dr. R. Gross
Die Dissertation wurde am 05.06.2008 beiderTechnischenUniversitatMu¨ncheneingereicht ¨ unddurchdieFakult¨atf¨urPhysikam04.07.2008angenommen.
Abstract
The radiative properties of an atom are not only determined by its internal struc-ture, but also by its environment. By modifying the density of the surrounding electromagnetic modes, the interaction of an atom with light can be increased sig-nificantly. Such a situation is realized for an atom placed inside a cavity which supports only a single mode. If the coupling of the atom to this privileged mode exceeds the interaction of atom and cavity with the external modes, a new system with its own characteristic energy structure emerges. This constitutes the ’strong-coupling regime’ of cavity-QED. Here, the energy levels of the system form a ladder of doublets. The first doublet has a classical interpretation -the normal-mode split-ting resulting from a harmonic dipole oscillator being coupled to an electromagnetic field-, and has been experimentally observed in the spectrum of various types of cavity-QED systems. This thesis reports on the first experimental observation of a higher-doublet state in the transmission spectrum of an optical cavity-QED system, consisting of a single rubidiumatomwhichislocalizedinthemodeofahigh-finesseFabry-Pe´rottype microcavity by means of an intracavity dipole trap. When probing the system at low intensity, only single-photon transitions to the first doublet are driven, and the spectrum reveals the normal modes. For rising intensities, a state consisting of two photons strongly coupled to the atom is populated via a two-photon transition, vis-ible as an additional resonance at a characteristic frequency and with an amplitude rising quadratically with the probe intensity. The observed transmission spectra are compared to different theory models. Only the quantum model, in which a two-level atom is coupled to a quantized cavity mode, is able to reproduce the measurements, whereas theories for a classical field fail to explain the data. These results prove the quantum nature of the combined atom-cavity system in the optical domain and show that states consisting of a single atom entangled with a quantized field are experimentally accessible, paving the way for more fundamental studies on this model system for light-matter interaction.