Cavity quantum electrodynamics (cQED) systems are promising candidates for nodes in a quantum information processing network. An inherent limitation of current Fabry-Perot based cQED systems, however, is scalability. We are working to realize cQED phenomena using toroidal whispering-gallery-mode (WGM) optical microcavities and cesium atoms. Toroidal WGM optical microcavities are compact chip-based resonators which resonantly confine light to small volumes with extremely low losses, giving rise to strong coupling and extremely high quality factors. We have conducted simulations for atom-cavity coupling strength g, critical atom number N0, and critical photon number n0 for a toroid interacting with a cesium atom and find the potential for better strong coupling than is currently possible using Fabry-Perot cavities. In optimized structures, modeling predicts coupling rates g/2pi exceeding 700 MHz and critical atom numbers approaching 10^-7. Experimental measurements of toroidal cavities at a wavelength of 852 nm indicate that quality factors in excess of 10^8 can be obtained in a cavity with a 50micrometer principal diameter, which would result in strong-coupling values of (g/ 2pi, n0, N0) =(86 MHz, 4.6*10^-4 , 1.0*10^-3) [1].

Shown here is an array of toroids (the 15 small vertical dots),
one of which is coupled to a tapered fiber (horizontal line in middle of photo).
The MOT of Cesium atoms is visible as a glowing cloud.

Our current goal is to observe and quantify these calculated cQED parameters experimentally. We do so by dropping a cloud of cold atoms from a magneto-optical trap (MOT) onto a toroidal resonator while monitoring the optical transmission through a fiber coupled to the resonator mode. When a single atom interacts with the resonator as it falls, we expect to observe the output to change in a manner which is characteristic of its cQED parameters discussed above.

Future possibilities for this experiment include trapping an atom to the cavity mode and coupling multiple resonators on a single chip.

[1] S. M. Spillane et al, Phys. Rev. A, 71, 013817 (2005)