Deterministic Coupling of a Single Atom to a Nanoscale Optical Cavity

Deterministic control over interactions between isolated ultra-cold atoms and nanoscale solid-state systems is an outstanding problem in quantum science. It is of interest for understanding the fundamental limits of quantum control over complex systems, as well as for realizing hybrid quantum systems, combining the excellent coherence properties atoms with strong interactions and scalability. We propose and demonstrate a technique for deterministically interfacing a single rubidium atom with a nanoscale photonic crystal cavity by trapping the atom in the near-field of the cavity. By controlling the atom's position, we probe the cavity field non-invasively with a resolution below the diffraction limit. A single-photon single-atom coupling rate of $2g \simeq 2\pi \times 0.5$ GHz is measured by a reduction in the cavity transmission. We discuss prospects for integrated, strongly-coupled quantum nano-optical circuits, and their potential applications.