J Austral Math Soc Ser B 33 pp180--191, 1991.

Uncertainty principles invariant under the fractional Fourier transform

David Mustard

Abstract

Uncertainty principles like Heisenberg's assert an inequality obeyed by some measure of joint uncertainty associated with a function and its Fourier transform. The more groups under which that measure is invariant, the more that measure represents an intrinsic property of the underlying object represented by the given function. The Fourier transform is imbedded in a continuous group of operators, the fractional Fourier transforms, but the Heisenberg measure of overall spread turns out not to be invariant under that group. A new family is developed of measures that are invariant under the group of fractional Fourier transforms and that obey associated uncertainty principles. The first member corresponds to Heisenberg's measure but is generally smaller than his although equal to it in special cases.

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Author

David Mustard

School of Mathematics, University of N.S.W., P.O. Box 1, Kensington, Australia 2033.