Renyi-alpha entropies of quantum states in closed form: Gaussian states and a class of non-Gaussian states

TL;DR

This paper derives closed-form expressions for Renyi-alpha entropies of Gaussian and certain non-Gaussian quantum states of bosons in phase space, enabling systematic analysis of entropy dynamics in Gaussian systems starting from non-Gaussian states.

Contribution

It provides the first closed-form formulas for Renyi-alpha entropies of Gaussian and specific non-Gaussian states, extending previous results and facilitating entropy dynamics studies.

Findings

Closed-form formulas for Gaussian states for alpha=2,3,4,...

Extension of formulas to certain non-Gaussian states with negative Wigner functions

Enabling systematic study of entropy evolution in Gaussian dynamics from non-Gaussian initial states

Abstract

In this work, we study the Renyi-alpha entropies S_{alpha}(\hat{rho}) = (1 - alpha)^{-1} \ln{Tr(\hat{rho}^{alpha})} of quantum states for N bosons in the phase-space representation. With the help of the Bopp rule, we derive the entropies of Gaussian states in closed form for positive integers alpha = 2,3,4, ... and then, with the help of the analytic continuation, acquire the closed form also for real values of alpha > 0. The quantity S_2(\hat{rho}), primarily studied in the literature, will then be a special case of our finding. Subsequently we acquire the Renyi-alpha entropies, with positive integers alpha, in closed form also for a specific class of the non-Gaussian states (mixed states) for N bosons, which may be regarded as a generalization of the eigenstates |n> (pure states) of a single harmonic oscillator with n >= 1, in which the Wigner functions have negative values indeed. Due to the fact that the dynamics of a system consisting of $N$ oscillators is Gaussian, our result will contribute to a systematic study of the Renyi-alpha entropy dynamics when the current form of a non-Gaussian state is initially prepared.