Ytterbium clocks achieve greater precision than cesium

New Scientist : Atomic clocks measure time by the number of oscillations between two atomic energy levels. Because cesium atoms oscillate almost 10¹⁰ times per second, cesium-based atomic clocks have long been considered the most precise standard of measurement. But in the quest for ever greater precision, scientists are looking at other elements with even faster oscillation rates. Andrew Ludlow at NIST and colleagues have now developed two optical lattice clocks that use ytterbium, which oscillates about 10¹⁸ times per second. Although the ytterbium clocks are many times more precise than cesium, they may not yet be as accurate. More study is needed to identify and eliminate potential sources of error. Once they have been fine-tuned, ytterbium clocks could be used to make ultraprecise measurements of such physical phenomena as gravity and fundamental constants.