Lineshape splitting with single atoms in concentric cavities

Summary form only given. Cavity Quantum Electrodynamics (CQED) has been at the forefront of modem atomic physics and quantum optics. Of particular importance of CQED is the strong coupling regime whereby the coupling rate between atoms and cavity field dominates other dissipative rates [1]. To date, the requirements to obtain such significant interaction have been presumed to have micro-cavities with a high finesse and small mode volumes. Though having demonstrated remarkable results and progress, such cavities with limited optical access, high reflectivity coating and close distance between mirrors pose a challenge for scaling up and embedding other systems with CQED such as ion traps.In this work, we take an alternative approach of employing cavity designs with strong focusing modes [2]. Central to our experiment is a cavity in the near concentric point with a finesse of 150. The cavity has a length of 11mm, a radius of curvature of 5.5mm and accommodates a focusing mode of approximately 5um beam waist. We trapped a single Rb87 atom at the centre of the cavity by an intra-cavity dipole trap. We observed the lineshape splitting in the transmission spectrum of cavity under the present of the trapped single atoms. The cooperativity of 0.1 can be deduced from Fig 1 and place our system in the intermediate coupling regime. This first observation of lineshape splitting with centimetre long and low finesse cavity promises the broader use of CQED and new exploration of CQED physics at strong focusing regime, where all optical cavity modes become degenerate.