Keeping track of time seems simple. A watch ticks, a pendulum swings, and a calendar flips. But at the quantum level, marking time is far more complicated — and far more expensive than anyone expected ...

For many years, cesium atomic clocks have been reliably keeping time around the world. But the future belongs to even more accurate clocks: optical atomic clocks. In a few years' time, they could ...

Vladan Vuletić with members of his Experimental Atomic Physics group. From left to right: Matthew Radzihovsky, Leon Zaporski, Qi Liu, Vladan Vuletić, and Gustavo Velez. Every time you check the time ...