A. Kawasaki, B. Braverman, E. Pedrozo-Peñafiel, C. Shu, S. Colombo, Z. Li, I. Ozel, W. Chen, D. Levonian, Y. Xiao, V. Vuletic, L. Salvi, A. Heinz, D. Akamatsu Geometrically asymmetric optical cavity for strong atom-photon coupling 2019