In 1989, David J. Wineland and his group at NIST observed the quantum Zeno effect for a two-level atomic system that was interrogated during its evolution. Approximately 5,000 ions were stored in a cylindrical Penning trap and laser-cooled to below 250 mK. A resonant RF pulse was applied, which, if applied alone, would cause the entire ground-state population to migrate into an excited state. After the pulse was applied, the ions were monitored for photons emitted due to relaxation. The ion trap was then regularly "measured" by applying a sequence of ultraviolet pulses during the RF pulse. As expected, the ultraviolet pulses suppressed the evolution of the system into the excited state. The results were in good agreement with theoretical models. A recent review describes subsequent work in this area.