In Wigner phase space, convolution explains why the vacuum majorizes mixtures of Fock states

Abstract

I show that a nonnegative Wigner function that represents a mixture of Fock states is majorized by the Wigner function of the vacuum state. As a consequence, the integration of any concave function over the Wigner phase space has a lower value for the vacuum state than for a mixture of Fock states. The Shannon differential entropy is an example of such concave function of significant physical importance. I demonstrate that the very cause of the majorization lies in the fact that a Wigner function is the result of a convolution. My proof is based on a new majorization result dedicated to the convolution of the negative exponential distribution with a precisely constrained function. I present a geometrical interpretation of the new majorization property in a discrete setting and extend this relation to a continuous setting. Findings presented in this article might be expanded upon to explain why the Wigner function of the vacuum majorizes - beyond mixtures of Fock states - many other physical states represented by a nonnegative Wigner function.