Atomic clock
An atomic clock is a highly precise timekeeping device that uses the resonance frequencies of atoms or molecules to measure time. The concept was first proposed by physicist Isidor Isaac Rabi in 1945, leading to the development of the first atomic clock in 1949 by the National Bureau of Standards, which utilized the microwave resonance frequencies of ammonia. This early design included a microwave cavity and a quartz oscillator that maintained the oscillator's frequency to match the natural vibrational frequency of the ammonia, thus ensuring accurate timekeeping.
Over the years, various types of atomic clocks have been developed, with the fundamental principles largely remaining the same. A significant advancement occurred in 1952 when a clock was created using cesium atoms, which later became the standard for defining the second in 1967 as exactly 9,192,631,770 oscillations of the resonance frequency of cesium. Atomic clocks are now widely used in various applications, including global positioning systems (GPS), telecommunications, and scientific research, due to their unmatched precision and stability.
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Atomic clock
A clock that uses resonance frequences of atoms to measure time accurately
Atomic clocks keep time more accurately than any other means of measuring time, including those based on the rotation of the Earth or the movement of the stars. Eventually, innumerable communication, scientific, and navigation systems would rely on the precision of atomic clocks.
In 1945, Isidor Isaac Rabi, a physics professor at Columbia University, proposed making a clock that derived its time scale from resonance frequencies of atoms or molecules. Using Rabi’s idea, the National Bureau of Standards (now the National Institute of Standards and Technology) announced the first atomic clock in 1949. It relied on the microwave resonance frequencies of the ammonia molecule.
The core of the first atomic clock was a microwave cavity containing ammonia, a tunable microwave oscillator, and a feedback circuit to adjust the oscillator frequency to the resonance frequency of ammonia. When microwave energy is supplied to the ammonia at its natural vibrating frequency of 23,870 hertz, the ammonia absorbs the energy. A quartz oscillator was used to supply energy to the ammonia gas. When the frequency of the oscillator varied from the resonance value for ammonia, energy was no longer absorbed by the ammonia. A signal was then fed back to the oscillator supply to prevent it from drifting from the resonance frequency, thus maintaining the accuracy of the clock.
Impact
Although different kinds of atomic clocks have been developed, the fundamental operating principle of these devices is the same as that of the ammonia atomic clock. In 1952, an atomic clock using cesium atoms as the vibration source was produced. In 1967, the second was defined as exactly 9,192,631,770 oscillations of the resonance frequency of cesium.
Bibliography
Audoin, Claude, and Bernard Guinot. The Measurement of Time: Time, Frequency, and the Atomic Clock. New York: Cambridge University Press, 2001.
Major, Fouad G. The Quantum Beat: Principles and Applications of Atomic Clocks. New York: Springer, 2007.