Optical atomic clocks could redefine unit of time

Neat! Optical atomic clocks could redefine unit of time: http://physics.aps.org/articles/v5/126 "Optical atomic clocks now outperform the best microwave cesium atomic clocks in terms of precision.
Never measure anything but frequency!” was the advice [1] of the late Arthur Schawlow, the 1981 Nobel Prize winner in physics. Frequency is, in fact, the physical quantity that can be measured with by far the greatest accuracy. This is because it can be referenced to a highly accurate standard: the cesium atomic clock, in which a second is defined as 9192631770 periods of the microwave radiation emitted by a cesium-133 atom transitioning between two nuclear spin (hyperfine) states [2]. Now, in Physical Review Letters, Alan Madej and colleagues at the National Research Council in Canada report they have greatly increased the accuracy with which another atomic frequency standard, the optical transition in an isolated strontium ion, can be measured. Furthermore, the precision of their frequency measurement now supersedes that of the existing cesium standard, which could lead to the adoption of a new frequency standard for defining the second as the basic unit of time"