Search for superradiance of two trapped ions

Laser-cooled trapped ion crystals offer a unique opportunity to study the interactions between atoms. The ions are essentially motionless and lie at a known and controllable distance from each other, permitting qualitatively new studies of atom-atom interactions not accessible in a gas cell or atomic beam. We have previously developed a microscopic planar Paul trap which is small and strong enough to bring the ion separation into the sub-micron region where the atoms interactions (other than Coulomb) become important. We have recently produced a 2-ion crystal with a separation of 1.0 microns, which is 5-10 times smaller than previously observed and amounts to only 2.2 wavelengths of the 493 nm Ba{sup +} transition used for laser cooling. A search is underway for the superradiant coupling of two atoms which manifests itself as a variation of the spontaneous emission rate with the ion-ion distance. The spontaneous emission rate is measured by a high repetition-rate transient spectrometer with an error of less than 1% for a single ion in a few minutes. This should be sufficient to resolve superradiant effects which are as large as 10% at this separation.