Increased atom-cavity coupling and stability using a parabolic ring cavity

Abstract

Optical cavities are one of the best ways to increase atom-light coupling and will be a key ingredient for future quantum technologies that rely on light–matter interfaces. We demonstrate that traveling-wave ‘ring’ cavities can achieve small mode waists w (i.e. large atom-cavity coupling) while maintaining stability to fluctuations and large mirror separation. Additionally, our ring cavity design can achieve arbitrary transverse-mode spacing simultaneously with the large mode-waist reductions. Following these principles, we build a parabolic atom-ring cavity system that achieves strong collective coupling NC = 15(1) between N = 103 Rb atoms and a ring cavity with a single-atom cooperativity C that is significantly larger than what could be achieved with a near-confocal two-mirror cavity with the same mirror separation and finesse. By using parabolic mirrors, we eliminate astigmatism–which can otherwise preclude stable operation–and increase optical access to the atoms. Cavities based on these principles, with enhanced coupling and large mirror separation, will be particularly useful for achieving strong coupling with ions, Rydberg atoms, or other strongly interacting particles, which often have undesirable interactions with nearby surfaces.