Abritish cesium clockwhich marks the atomic time is now the most accurate long-term time meter in the world, according to a new evaluation of the watch to be published in the international scientific journalMetrologyand conducted by physicists from the National Physics Laboratory (NPL) in the United Kingdom and Pennsylvania State University, in the United States. The watch belongs to aelite cesium watch group, created by time labs in Europe, the United States, and Japan as their national frequency standard for time measurement.
These national standards are used toobtain International Atomic Time and Coordinated Universal Time, used as timescales throughout the world for processes such asglobal communication, thesatellite navigationand thetopography, and for the time stamping of computer transactions between financial and stock markets. The methods used to improve the UK clock can also be used to evaluate cesium source clocks from other countries.
“The improvements our work describes have significantly reduced the two largest sources of measurement uncertainty for the cesium source clock:the doppler effectand the frequency shift of microwave lenses, “explained project leader Krzysztof Szymaniec.
Scientists estimate the precision of a cesium source clock by evaluating the uncertainty of all physical effects that cause changes in the clock’s operating frequency, including atomic interactions with external fields,collisions between atoms, and the construction of the subsystems of the atomic clock, such as its microwave cavity. The two main sources of these uncertainties are frequency changes caused by the Doppler effect and microwave lenses. Microwave lenses are the result of the forces that microwaves exert on atoms to measure the length of one second.
“An international agreement on the definition of a second is of fundamental importance in the measurement of time,” explained Szymaniec, detailing thatthe duration of one second, by international agreement, it is the “transition frequency between two sublevels of a cesium 133 atom”. To measure this frequency, source cesium clocks measure laser-cooled cesium atoms twice as they travel through the clock’s microwave cavity, once on its way up and again on its way down.
