Programmable few-atom Bragg scattering and ground-state cooling in a cavity*

We report few-atom Bragg scattering from atoms trapped in tweezers into the two running-wave modes of a high-cooperativity bow-tie cavity. We observe asymmetric interference in cavity scattering into the two modes set by the angle of the illuminating light and the narrowing of the Bragg peak with increasing atom number at the level of a few atoms, demonstrating both superradiant and subradiant features. These measurements allow precise calibration of the incident beam angle and the array's geometric structure. The high-contrast Bragg scattering is enabled by three-dimensional cavity cooling of the entire atom array to the motional ground state. With a narrow cavity linewidth, we operate in the resolved sideband regime and apply cavity cooling to cool the radial motion to its ground state with a phonon occupation below 0.2. With enhanced control of light-matter interaction in atom arrays, our work paves the way for a series of applications from fundamental light scattering to quantum metrology and computation.