NIST-7, an atomic clock that will neither gain nor lose a second in 1 million years, recently debuted at NIST's Boulder, Colo., laboratory. When fully evaluated in a year, it is expected to show an accuracy of one second in 3 million years--making NIST-7 the world's most accurate clock. Who needs such accuracy? Examples of atomic clock time users are NASA (for guiding deep space probes), the Department of Defense (for operating a satellite-based navigation network), the investment banking firm Salomon Brothers (for time stamping international financial transactions) and California's Los Angeles County (for timing traffic signals). NIST-7 is the seventh generation of atomic clocks built by NIST (and its predecessor, the National Bureau of Standards) since 1949, and replaces NBS-6, which was accurate to one second in 300,000 years. While both clocks measure time by counting the vibrations of a beam of cesium-133 atoms (one second elapses after 9,192,631,770 vibrations), NIST-7 uses lasers rather than magnetic fields to better manipulate the beam and increase the clock's accuracy.
A new cooperative research and development agreement between NIST and Rincon Research Corp. of Tucson, Ariz., seeks to develop advanced atomic clocks that use super-cold cesium atoms to measure time. The collaborators hope that the new timekeepers will provide private industry with a field standard comparable to current national laboratory standards. Traditional atomic clocks (see previous NIST Update item) measure time by counting vibrations of cesium atoms streaming through a tube at speeds of around 200 meters per second. For the advanced clocks, NIST physicists are slowing these atoms to about one centimeter per second by laser cooling them to very near absolute zero. NIST and Rincon plan to design clocks that will be much smaller than those currently keeping the international time standard, yet potentially just as accurate.
