Experimental Demonstration of Topological Charge Protection in Wigner Current

Abstract

We experimentally reconstruct Wigner's current of quantum phase space dynamics for the first time. We reveal the ``push-and-pull" associated with damping and diffusion due to the coupling of a squeezed vacuum state to its environment. In contrast to classical dynamics, where (at zero temperature) dissipation only ``pulls" the system toward the origin of phase space, we also observe an outward ``push" because our system has to obey Heisenberg's uncertainty relations. With squeezed vacuum states generated by an optical parametric oscillator at variable pumping levels, we identify the pure squeezing dynamics and its central stagnation point with a topological charge of `$-1$'. We experimentally verify that this charge is protected for weakly as well as strongly decohering conditions. This work demonstrates high resolving power and establishes an experimental paradigm for measuring quantumness and non-classicality of the dynamics of open quantum systems.