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We investigate the suitability of toroidal microcavities for strong-coupling cavity quantum electrodynamics (QED). Numerical modeling of the optical modes demonstrate a significant reduction of the modal volume with respect to the whispering gallery modes of dielectric spheres, while retaining the high-quality factors representative of spherical cavities. The extra degree of freedom of toroid microcavities can be used to achieve improved cavity QED characteristics. Numerical results for atom-cavity coupling strength g, critical atom number N₀, and critical photon number n₀ for cesium are calculated and shown to exceed values currently possible using Fabry-Perot cavities. Modeling predicts coupling rates g∕2 exceeding 7000. 3em{0ex}MHz and critical atom numbers approaching 10^-7 in optimized structures. Furthermore, preliminary experimental measurements of toroidal cavities at a wavelength of 8520. 3em{0ex}nm indicate that quality factors in excess of 10^8 can be obtained in a 501000-0pt principal diameter cavity, which would result in strong-coupling values of (g∕ (2), n₀, N₀) = (860. 3em{0ex}MHz, 4. 610^-4, 1. 010^-3).
Spillane et al. (Wed,) studied this question.