Science 341, 1215–1218 (2013)
Atomic clocks have long been instrumental in science and technology, leading to innovations such as global positioning, advanced communications and tests of variations in fundamental constants. The uncertainty of an optical lattice clock is usually constrained by a technical noise source known as the Dick effect. Now, Nathan Hinkley and co-workers from the USA and Italy have succeeded in further suppressing the Dick effect to achieve an unprecedented atomic clock instability of 1.6 × 10−18 after 7 h of averaging. The researchers prepared two independent optical lattice clocks composed of ultracold 171Yb atoms. A clock laser light at 578 nm was prestabilized to an isolated, high-finesse optical cavity using Pound–Drever–Hall detection and electronic feedback to an acoustic-optic modulator and a laser piezoelectric transducer. The laser light was divided into two paths. These beams were then frequency shifted using independent acoustic-optic modulators so that they became resonant with the clock transitions of two atomic systems, which are sensitive to the local environment. Consequently, despite being derived from the same local oscillator, the experimental cycles of each clock system were imperceptibly unsynchronized and had different durations. The frequency difference between the two Yb clock systems was measured to see how the ticking of the two Yb clocks stabilized over time.
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