JILA physicists have measured the effect called time dilation, at the smallest scale ever, showing that two tiny atomic clocks, separated by just a millimeter or the width of a sharp pencil tip, tick at different rates.
The most important and exciting result is that we can potentially connect quantum physics with gravity, for example, probing complex physics when particles are distributed at different locations in the curved space-time,” NIST/JILA Fellow Jun Ye said. “For timekeeping, it also shows that there is no roadblock to making clocks 50 times more precise than today
According to general relativity, atomic clocks at different elevations in a gravitational field tick at different rates. The frequency of the atoms’ radiation is reduced — shifted toward the red end of the electromagnetic spectrum — when observed in stronger gravity, closer to Earth. That is, a clock ticks more slowly at lower elevations
“If we could measure the redshift 10 times even better than this, we will be able to see the atoms’ whole matter waves across the curvature of space-time. Being able to measure the time difference on such a minute scale could enable us to discover, for example, that gravity disrupts quantum coherence, which could be at the bottom of why our macroscale world is classical.”
https://www.nist.gov/news-events/news/2022/02/jila-atomic-clocks-measure-einsteins-general-relativity-millimeter-scale
https://www.youtube.com/watch?v=thb8Wr4kg94 
