Whispering-gallery-mode (WGM) microresonators provide a powerful system for the investigation of cavity quantum electrodynamics because they allow one to combine both, strong coupling between quantum emitters and light as well as low optical loss, in the same system. Furthermore, due to the strong confinement of the light in these resonators, a strong longitudinal polarization component of the electric field occurs that oscillates in quadrature to the transversal component. Most significantly, the emerging transverse photon spin is intrinsically coupled to the direction of propagation of light. When the resonator field is coupled to a polarization-dependent emitter, such as a spin-polarized atom, this gives rise to chiral light--matter interaction.
I my talk I will summarize our main experimental results on chiral light--matter interaction that occurs when coupling single rubidium atoms to a bottlemicroresonator. By making use of the chiral light--matter interaction, we have demonstrated a strong optical Kerr nonlinearity that imprints a photon number dependent phase shift close to the maximum value of pi at the level single photons. Furthermore, we realized a new class of nonreciprocal devices, including a fiber integrated optical diode as well as a circulator that are controlled by a single atom.
In addition, I will discuss our recent attempt to trap single atoms in the evanescent field of our WGM-microresonator. Trapping atoms directly in the evanescent field would drastically extend the atom-resonator interaction time and would allow us to implement more complex protocols.
Host: M. Aspelmeyer