Ultrahigh-Qtoroidal microresonators for cavity quantum electrodynamics

Abstract

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 $N_0$, 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 $700\mathrm{MHz}$ and critical atom numbers approaching ${10}^{-7}$ in optimized structures. Furthermore, preliminary experimental measurements of toroidal cavities at a wavelength of $852\mathrm{nm}$ indicate that quality factors in excess of ${10}^8$ can be obtained in a $50\text{‐}\mu \mathrm{m}$ principal diameter cavity, which would result in strong-coupling values of $\mathbf{(}g∕\left(2\pi \right),n_0,N_0\mathbf{)}=(86\mathrm{MHz},4.6\times {10}^{-4},1.0\times {10}^{-3})$.