Notes on Hardy's Uncertainty Principle for the Wigner distribution and Schrödinger evolutions

Abstract: We consider Schr\"{o}dinger equations with real quadratic Hamiltonians, for which the Wigner distribution of the solution at a given time equals, up to a linear coordinate transformation, the Wigner distribution of the initial condition. Based on Hardy's uncertainty principle for the joint time-frequency representation, we prove a uniqueness result for such Schr\"{o}dinger equations, where the solution cannot have strong decay at two distinct times. This approach reproduces known, sharp results for the free Schr\"{o}dinger equation and the harmonic oscillator, and we also present an explicit scheme for quadratic systems based on positive definite matrices.