Cavity quantum electrodynamics in a high numerical aperture resonator

From fundamental studies of light-matter interaction to applications in quantum networking and sensing, cavity quantum electrodynamics (QED) provides a toolbox to control interactions between atoms and photons. The coherence of interactions is determined by the single-pass atomic absorption and the number of photon round-trips. Reducing the cavity loss has enabled resonators supporting~1-million roundtrips, but with limited material choices and increased alignment sensitivity. Here we present a high numerical-aperture,lens-based resonator that pushes the single-atom-single-photon absorption probability near its fundamental limit by reducing the mode size at the atom to order lambda. This resonator provides a single-atom cooperativity of 1.6 in a cavity where the light circulates only~10times. We load a single 87Rb atom into this cavity, observe strong coupling, and demonstrate cavity-enhanced detection with fidelity of 99.55(6)% and survival of 99.89(4)% in 130 microseconds. Introducing intra-cavity imaging systems will enable cavity arrays compatible with Rydberg atom arrays computing technologies, expanding the the applicability of the cavity QED toolbox.

Methods
This data was collected using a single photon counter and processed using Jupyter Notebook (python)