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Quantum coherence
Return to Quantum decoherence theory, Quantum, Quantum Computing, Quantum Computer, Quantum Mechanics
Also called: Coherence (physics). See also Coherence
- Snippet from Wikipedia: Coherence (physics)
In physics, coherence expresses the potential for two waves to interfere. Two monochromatic beams from a single source always interfere.: 256 Physical sources are not strictly monochromatic: they may be partly coherent. Beams from different sources are mutually incoherent.
When interfering, two waves add together to create a wave of greater amplitude than either one (constructive interference) or subtract from each other to create a wave of minima which may be zero: 256 (destructive interference), depending on their relative phase. Constructive or destructive interference are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable.
Two waves with constant relative phase will be coherent. The amount of coherence can readily be measured by the interference visibility, which looks at the size of the interference fringes relative to the input waves (as the phase offset is varied); a precise mathematical definition of the degree of coherence is given by means of correlation functions. More generally, coherence describes the statistical similarity of a field (electromagnetic field, quantum wave packet etc.) at two points in space or time.
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