The Atomic Clock

Kurt Gibble, of Penn State University, is pictured here with an atomic clock.  Gibble is the principal investigator of a research team that developed an innovative way to study atomic collisions in a cesium fountain clock--the kind of atomic clock used to keep the world's standard of time. 

Atomic clocks use the quantum oscillations of ultra-cold atoms, which tick at regular intervals, to gauge the passage of time.  The Penn State team was able to accurately measure the shift in the atom's quantum oscillations, or phase shifts, that it experiences during a collision with another atom. These phase shifts, which cause jumps in the atom's ticks, limit the accuracy of the world's most accurate atomic clocks. 

Until this study, these shifts had been impossible to measure with high precision because earlier techniques relied on knowing the atom's density, which cannot be measured accurately.  For further information, see the Penn State news story "New Method to Directly Probe the Quantum Collisions of Individual Atoms."