Fig. 1. Experimental scheme. (a) Quantum beat fluorescence measurement in a Rb vapor. The fluorescence is detected with a photo multiplier tube (PMT) and the signal Sn(τ,nφ21) is amplified and fed into a lock-in amplifier (LIA), where the phase modulation φ21(t) is removed from the signal and Sn is decomposed into its harmonic components Sk, k = 1–3. Optionally, the probe pulse is orthogonally polarized to the pump pulse (indicated by dashed pulse envelope), where QA denotes the quantization axis of the system. (b) Quantum beat photoionization measurement of a thermal atomic Rb beam in a vacuum apparatus using a separate UV pulse (260 nm) for ionization. Photoelectrons are detected in a magnetic bottle (MB) spectrometer with a multi-channel plate (MCP) detector. (c and d) Interfering quantum pathways excited in the Rb atoms for one- and two-photon excitations, respectively. (e) Schematic representation of a single-atom energy structure comprised of three electronic states, along with one- (red) and two-photon excitations (blue). The states |g = 1–3. Optionally, the probe pulse is orthogonally polarized to the pump pulse (indicated by dashed pulse envelope), where QA denotes the quantization axis of the system. (b) Quantum beat photoionization measurement of a thermal atomic Rb beam in a vacuum apparatus using a separate UV pulse (260 nm) for ionization. Photoelectrons are detected in a magnetic bottle (MB) spectrometer with a multi-channel plate (MCP) detector. (c and d) Interfering quantum pathways excited in the Rb atoms for one- and two-photon excitations, respectively. (e) Schematic representation of a single-atom energy structure comprised of three electronic states, along with one- (red) and two-photon excitations (blue). The states |g〉 to |f〉 represent the individual energy states of the Rb atoms. (f) Two atoms, represented as two-level systems, described in the site- and excitonic basis. In the latter, an interatomic interaction to |f = 1–3. Optionally, the probe pulse is orthogonally polarized to the pump pulse (indicated by dashed pulse envelope), where QA denotes the quantization axis of the system. (b) Quantum beat photoionization measurement of a thermal atomic Rb beam in a vacuum apparatus using a separate UV pulse (260 nm) for ionization. Photoelectrons are detected in a magnetic bottle (MB) spectrometer with a multi-channel plate (MCP) detector. (c and d) Interfering quantum pathways excited in the Rb atoms for one- and two-photon excitations, respectively. (e) Schematic representation of a single-atom energy structure comprised of three electronic states, along with one- (red) and two-photon excitations (blue). The states |g〉 to |f〉 represent the individual energy states of the Rb atoms. (f) Two atoms, represented as two-level systems, described in the site- and excitonic basis. In the latter, an interatomic interaction represent the individual energy states of the Rb atoms. (f) Two atoms, represented as two-level systems, described in the site- and excitonic basis. In the latter, an interatomic interaction V lifts the degeneracy of the singly excited states. Note, that here the states |g lifts the degeneracy of the singly excited states. Note, that here the states |g〉 to |f〉 denote two-body states. to |f lifts the degeneracy of the singly excited states. Note, that here the states |g〉 to |f〉 denote two-body states. denote two-body states.
