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In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves differ by less than the coherence length. A wave with a longer coherence length is closer to a perfect ...
The coherence time, usually designated τ, is calculated by dividing the coherence length by the phase velocity of light in a medium; approximately given by = where λ is the central wavelength of the source, Δν and Δλ is the spectral width of the source in units of frequency and wavelength respectively, and c is the speed of light in vacuum.
Coherence time is actually a statistical measure of the time duration over which the channel impulse response is essentially invariant, and quantifies the similarity of the channel response at different times. In other words, coherence time is the time duration over which two received signals have a strong potential for amplitude correlation.
The coherence length is defined as the distance the wave travels in time . [11]: 560, 571–573 The coherence time is not the time duration of the signal; the coherence length differs from the coherence area (see below).
The physical quantity coherence time is defined as the time that the quantum state holds its superposition principle. The purpose of against decoherence is to extend the coherence time of quantum systems. It will improve the stability of the computing of information. [45]
The coherence (sometimes called magnitude-squared coherence) between two signals x(t) and y(t) is a real-valued function that is defined as: [1] [2] = | | ()where G xy (f) is the Cross-spectral density between x and y, and G xx (f) and G yy (f) the auto spectral density of x and y respectively.
Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference Coherence (units of measurement), a derived unit that, for a given system of quantities and for a chosen set of base units, is a product of powers of base units with no other proportionality factor than one
Note that coherence of a given unit depends on the definition of the base units. Should the standard unit of length change such that it is shorter by a factor of 100 000, then the bar would be a coherent derived unit. However, a coherent unit remains coherent (and a non-coherent unit remains non-coherent) if the base units are redefined in ...