Scientists successfully used rapid light pulses to freeze trapped beryllium ions in their starting state.

In 1989, researchers tested this freezing effect on five thousand trapped beryllium ions. They used a radio wave pulse to coax the ions into changing states. However, when they repeatedly flashed the ions with quick pulses of ultraviolet laser light, the change stopped. The frequent laser looks kept the ions frozen in their original state. This proved that real-world quantum systems could be held still just by measuring them.