On Generalized Stam Inequalities and Fisher-R\'enyi Complexity Measures

TL;DR

This paper introduces a new three-parameter Fisher-Rényi complexity measure that generalizes Stam inequalities, providing bounds and explicit distributions, and applies it to quantum systems like harmonic and hydrogenic states.

Contribution

It proposes a novel three-parametric Fisher-Rényi complexity measure with invariance and bounding properties, extending Stam inequalities and identifying the minimizing distributions.

Findings

Derived the sharp lower bound of the complexity measure.

Identified the $(p,eta, heta)$-Gaussian distribution as the minimizer.

Applied the measure to quantum states of harmonic and hydrogenic systems.

Abstract

Information-theoretic inequalities play a fundamental role in numerous scientific and technological areas as they generally express the impossibility to have a complete description of a system via a finite number of information measures. In particular, they gave rise to the design of various quantifiers (statistical complexity measures) of the internal complexity of a (quantum) system. In this paper, we introduce a three-parametric Fisher-R\'enyi complexity, named $(p,\beta,\lambda)$-Fisher--R\'enyi complexity. This complexity measure quantifies the combined balance of the spreading and the gradient contents of $\rho$, and has the three main properties of a statistical complexity: the invariance under translation and scaling transformations, and a universal bounding from below. The latter is proved by generalizing the Stam inequality, which lowerbounds the product of the Shannon entropy power and the Fisher information of a probability density function. An extension of this inequality was already proposed by Bercher and Lutwak, a particular case of the general one, where the three parameters are linked, allowing to determine the sharp lower bound and the associated probability density with minimal complexity. Using the notion of differential-escort deformation, we are able to determine the sharp bound of the complexity measure even when the three parameters are decoupled (in a certain range). We determine as well the distribution that saturates the inequality: the $(p,\beta,\lambda)$-Gaussian distribution, which involves an inverse incomplete beta function. Finally, the complexity measure is calculated for various quantum-mechanical states of the harmonic and hydrogenic systems, which are the two main prototypes of physical systems subject to a central potential.