Atomic clocks are well-known for their reliability and accuracy. Such a clock is controlled by the oscillation of atoms such as cesium or rubidium. The atoms are in turn energized by an electromagnetic field or optical pumping. The first such clock developed in this manner was created in 1944 at Columbia University by Isidor Issac Rabi.
Atomic clocks are used primarily for the purpose of scientific research when time needs to be measured in increments as little as billionths of a second. Today, the most preferred types of atomic clocks are of the cesium fountain variety.
With that established, most people do not have atomic clocks in their homes. That alarm clock you use to wake up for work in the morning as well as that clock on the wall is likely a radio clock. A miniature receiver tuned to 77.5 kHz (77,500 Hertz) gets signals from a transmitter that gets the time from an actual atomic clock. Radio signals don’t break time down into tiny increments as atomic clocks, because the average person simply doesn’t need to know how many minuscule fractions of seconds have passed.
In regard to the comparative accuracy of atomic clocks, one in particular is said to stand above the rest. It is known as the NPL (National Physical Laboratory) CsF2 and is located near London, England. This is a cesium fountain clock used to measure International Atomic Time and Universal Coordinated Time. Krzysztof Szymaniec of the National Physical Laboratory was accompanied by scientists from Pennsylvania State University in evaluating the clock’s accuracy.
This atomic clock was found to be accurate to within two ten million billionths of a second! Cesium clocks are generally expected to lose or gain a second over a period of tens of millions of years. This particular clock outside of London will lose about a billionth of a second every two months. This feat was announced in August, 2011.
In other news, and interestingly just days later, it was announced that an optical lattice clock has been developed by Professor Hidetoshi Katori of the University of Tokyo, Japan that is accurate to 100 quadrillion of a second. An optical lattice clock is a variation of the conventional atomic clock with one big difference: Conventional atomic clocks observe single atoms and take averages over long periods of time. Optical Lattice clocks, on the other hand, can observe a million atoms at the same time. In fact, these types of clocks set the standard for television broadcasts and GPS systems, and are said to be the most accurate clocks on the planet.
So who wins, the British clock or the Japanese one? For those so inclined, feel free to do the math!