Introduction to atomic frequency standards

The fundamental precision of atomic timekeeping is unequaled in any other measurement methodology. Atomic frequency standards provide the ultimate source of accuracy and stability for all modern communications, navigation, and timekeeping systems. State-of-the-art atomic clocks test the frontiers of theoretical and experimental information theory, atomic physics, and cosmology. Practical implementations of atomic clocks range from commodity rubidium oscillators, smaller than a sandwich and accurate to parts in 1011, to one-of-a-kind laboratory-scale optical clocks, manned by teams of scientists and achieving accuracies now measured in parts in 10 17 .