Coherence and Interference: Generation of Mode Correlation and Velocity Selection
Quantum coherence is a property of quantum systems with no classical analog. Simply stated, the existence of coherence means that a measurement of one of the observables of the system gives information on the possible results of a subsequent measurement of another system observable. This property has played an essential rôle in modern Quantum Optics, e.g. in the demonstrations of reduced quantum noise measurements of light (squeezing). Also, coherence properties relating the internal and external (center-of-mass movement) atomic degrees of freedom have been used in cooling atoms to sub-recoil temperatures.