Nonlinear spectroscopy of photons bound to one atom

Abstract

Nonlinear optics traditionally involves macroscopic atomic ensembles or solid-state crystals. The observation of a nonlinear two-photon resonance in a system consisting of one single atom trapped inside an optical cavity demonstrates nonlinear optics at the level of individual quanta. Optical nonlinearities typically require macroscopic media, thereby making their implementation at the quantum level an outstanding challenge. Here, we demonstrate a nonlinearity for one atom enclosed by two highly reflecting mirrors1. We send laser light through the input mirror and record the light from the output mirror of the cavity. For weak laser intensity, we find the vacuum-Rabi resonances2,3,4,5,6,7,8,9,10,11. But for higher intensities, we observe an extra resonance12, which originates from the fact that the cavity can accommodate only an integer number of photons and that this photon number determines the characteristic frequencies of the coupled atom–cavity system13,14,15. We selectively excite such a frequency by depositing two photons at once into the system and find a transmission that increases with the laser intensity squared. The nonlinearity differs from classical saturation nonlinearities16,17,18,19 and is direct spectroscopic proof of the quantum nature of the atom–cavity system. It provides a photon–photon interaction by means of one atom, and constitutes a step towards a two-photon gateway or a single-photon transistor20.

Cite this article

Schuster, I., Kubanek, A., Fuhrmanek, A. et al. Nonlinear spectroscopy of photons bound to one atom. Nature Phys 4, 382–385 (2008). https://doi.org/10.1038/nphys940

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