  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 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, critical
atom number N_0 and critical photon number n_0 for cesium are calculated and
shown to exceed values currently possible using Fabry-Perot cavities. Modeling
predicts coupling rates g/(2*pi) exceeding 700 MHz and critical atom numbers
approaching 10^{-7} in optimized structures. Furthermore, preliminary
experimental measurements of toroidal cavities at a wavelength of 852 nm
indicate that quality factors in excess of 100 million can be obtained in a 50
micron principal diameter cavity, which would result in strong coupling values
of (g/(2*pi),n_0,N_0)=(86 MHz,4.6*10^{-4},1.0*10^{-3}).

Quantum Physics