Rezus YL Walt SG Lettow R Renn A Zumofen G Götzinger S Sandoghdar V 2012 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. application/pdf https://sonar.ch/global/documents/265568 eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevLett.108.093601 info:eu-repo/semantics/altIdentifier/pmid/22463633 info:eu-repo/semantics/openAccess Physical review letters. - 2012 Single-photon spectroscopy of a single molecule. http://purl.org/coar/resource_type/c_6501