Efficient interaction of light and matter at the ultimate limit of single photons and single emitters is of great interest from a fundamental point of view and for emerging applications in quantum engineering. However, the difficulty of generating single-photon streams with specific wavelengths, bandwidths, and power as well as the weak interaction probability of a single photon with an optical emitter pose a formidable challenge toward this goal. Here, we demonstrate a general approach based on the creation of single photons from a single emitter and their use for performing spectroscopy on a second emitter situated at a distance. While this first proof of principle realization uses organic molecules as emitters, the scheme is readily extendable to quantum dots and color centers. Our work ushers in a new line of experiments that provide access to the coherent and nonlinear couplings of few emitters and few propagating photons.

Ultrafast Spectroscopy

Rezus, Y., Walt, S. G., Lettow, R., Renn, A., Zumofen, G., Götzinger, S., & Sandoghdar, V. (2012). Single-Photon Spectroscopy of a Single Molecule. Phys.Rev.Lett., 108(9), 093601: 1–5. doi:10.1103/physrevlett.108.093601