The first atomic clock was an ammonia maser device built in 1949 at the U.S. National Bureau of Standards (NBS, now NIST). An atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time & frequency standards known, and are used as primary standards for international time distribution services, & to control the frequency of television broadcasts and GPS satellite signals.

Atomic clock

Since the beginning of development in the 1950′, atomic clocks have been made based on the hyperfine (microwave) transitions in hydrogen-1, caesium-133, & rubidium-87. For decades, scientific-instrument companies such as Hewlett-Packard have been making caesium-beam clocks & hydrogen masers for entities like NIST & USNO. In August 2004, NIST scientists demonstrated a chip-scaled atomic clock. According to the researchers, the clock was believed to be one-hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications. This device could conceivably become a consumer product.

In February 2008, physicists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) & the University of Colorado at Boulder, demonstrated a new clock based on strontium atoms trapped in a laser grid. The new clock is more than twice as accurate as the best clock up to now, the NIST-F1, & has an inaccuracy of less than one second in 200 million years (compared to 1 second per 80 million years for the F1).

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