 Visible light waves oscillate faster than microwaves, and therefore optical clocks can be more precise than caesium atomic clocks. The Physikalisch-Technische Bundesanstalt (PTB) is working on several such optical clocks. The model with one single ytterbium ion caught in an ion trap is highly accurate. The optical clock based on it is exact to 17 digits after the decimal point. A pair of experimental atomic clocks based on ytterbium atoms at the National Institute of Standards and Technology (NIST) has set a new record for stability. NIST physicists report in the August 22, 2013 issue of Science Express that the ytterbium clocks' ticks are stable to within less than two parts in 1 quintillion (1 followed by 18 zeros), roughly 10 times better than the previous best published results for other atomic clocks. The clocks would be accurate within a second for a period comparable to the age of the universe.
