"One exciting potential application for extremely precise atomic-based time measurements is measuring gravitational fields, which could be very useful in tunnel and cave detection,” DARPA program manager Ale Lukaszew said. “In principle, existing atomic clocks can keep time precisely enough to measure gravitational field differences over the distance of a few feet, but it could take weeks to process the measurement. If we can engineer a system that doesn’t lose its coherence as fast and can be re-tuned very quickly, we could potentially make those same measurements in half an hour.”
As esoteric as that sounds, the applications can be fairly down to earth, so we will continue to monitor the field for investment opportunities.