A Measured Decoherence Curve Must Be a L\'evy Exponent
Zongmin Liu
Abstract
Complete positivity and translation covariance force the localization rate $F(\Delta)$ of any Markovian open dynamics---environmental decoherence and objective collapse alike---to be a continuous negative definite function of the path separation $\Delta$, i.e.\ a L\'evy exponent. We turn this structural fact into a finite, model-free, and \emph{complete} test on data. Sampling $F$ at commensurate separations $F_k\equiv F(kd)$ reduces the L\'evy--Khintchine representation to a linear feasibility problem whose dual is a Chebyshev positivity cone; the cone is polyhedral only for two points. Three points already give closed-form walls, $(F_2-F_1)^2\le F_1F_3\le F_1(F_1+2F_2)$ together with $F_2\le 4F_1$, saturated respectively by a single momentum quantum and by Gaussian noise---the two extreme rays of the admissible cone. The test detects a $1\%$ super-quadratic admixture from three points, and it is necessary \emph{and} sufficient, so a curve that survives is realized by an actual noise measure. A visibility-versus- separation scan therefore falsifies Markovian translation-covariant evolution with no model and no fitting.