Optimal sizes of dielectric microspheres for cavity QED with strong coupling
Abstract
The whispering gallery modes (WGMs) of quartz microspheres are investigated for the purpose of strong coupling between single photons and atoms in cavity quantum electrodynamics (cavity QED). Within our current understanding of the loss mechanisms of the WGMs, the saturation photon number n_{0} and critical atom number N_{0} cannot be minimized simultaneously, so that an “optimal” sphere size is taken to be the radius for which the geometric mean (n_{0}N_{0}), is minimized. While a general treatment is given for the dimensionless parameters used to characterize the atomcavity system, detailed consideration is given to the D_{2} transition in atomic cesium at λ_{0}=852 nm using fusedsilica microspheres, for which the maximum coupling coefficient g_{a}/(2π)≈750 MHz occurs for a sphere radius a=3.63 μm corresponding to the minimum for n_{0}≈6.06×10^{6}. By contrast, the minimum for N_{0}≈9.00×10^{6} occurs for a sphere radius of a=8.12 μm, while the optimal sphere size for which (n_{0}N_{0}) is minimized occurs at a=7.83 μm. On an experimental front, we have fabricated fusedsilica microspheres with radii a∼10 μm and consistently observed quality factors Q⩾0.8×10^{7}. These results for the WGMs are compared with corresponding parameters achieved in FabryPerot cavities to demonstrate the significant potential of microspheres as a tool for cavity QED with strong coupling.
 Publication:

Physical Review A
 Pub Date:
 March 2003
 DOI:
 10.1103/PhysRevA.67.033806
 arXiv:
 arXiv:quantph/0210039
 Bibcode:
 2003PhRvA..67c3806B
 Keywords:

 42.50.Ct;
 42.55.Sa;
 32.80.t;
 Quantum description of interaction of light and matter;
 related experiments;
 Microcavity and microdisk lasers;
 Photon interactions with atoms;
 Quantum Physics
 EPrint:
 12 pages, 14 figures