Luke Masters (Humboldt University, Berlin)
The interaction of light with a single two-level emitter is the most fundamental process in quantum optics, and is key to many quantum applications. In this talk, I will present two distinct experiments that investigate this important setting [1, 2]. Firstly, the demonstration of strong coupling of a single atom to a whispering-gallery-mode microresontor was realised by generating a two-colour magic wavelength optical trap close to the resonator’s surface, and by measurement of a vacuum Rabi-splitting in the excitation spectrum of the coupled atom-resonator system. This first demonstration of stable and controlled interaction of a single atom with a whispering-gallery-mode in the strong coupling regime opens up the route towards the implementation of quantum protocols and applications that harvest the chiral atom-light interaction present in this class of resonators. In a second, more recent experiment, the light scattering of a single optically trapped atom in free-space was studied in detail. The measured photon statistics could be tuned from perfect antibunching to bunching, dependent on the setting of a narrowband optical filter in the detection path. These results offer insight into the scattering of two photons by a single two-level quantum emitter, and verify the picture that photon anticorrelations in resonance fluorescence can be thought of as arising from quantum interference between the coherent and incoherent two-photon scattering amplitudes.
 E. Will et al., Phys. Rev. Lett. 126, 233602 (2021)
 L. Masters et al., Nat. Phot. (2023)