Hermite functions and uncertainty principles for the\n Fourier and the windowed Fourier transforms
Aline Bonami, Bruno Demange, Philippe Jaming
Abstract
We extend an uncertainty principle due to Beurling into a characterization of\nHermite functions. More precisely, all functions $f$ on $\\mathbb{R}^d$ which may\nbe written as $P(x)\\exp (-\\langle Ax, x\\rangle)$, with $A$ a real symmetric\ndefinite positive matrix, are characterized by integrability conditions on the\nproduct $f(x) \\widehat{f}(y)$. We then obtain similar results for the windowed\nFourier transform (also known, up to elementary changes of functions, as the\nradar ambiguity function or the Wigner transform). We complete the paper with a\nsharp version of Heisenberg's inequality for this transform.