# Investigating bound entangled two-qutrit states via the best separable approximation

## TL;DR

This paper investigates the properties and distribution of bound entangled two-qutrit states using numerical and theoretical methods, revealing their negligible volume and sporadic occurrence on the separable state surface.

## Contribution

It introduces a combined numerical and theoretical approach to analyze bound entangled states in two-qutrit systems, highlighting their rare and island-like distribution.

## Key findings

- BE states have negligible volume in two-qutrit systems.
- BE states form tiny islands on the separable state surface.
- BE states are located under a layer of undistillable PPT states.

## Abstract

We use the linear programming algorithm introduced by Akulin et al. [V. M. Akulin, G. A. Kabatiansky, and A. Mandilara, Phys. Rev. A 92, 042322 (2015)] to perform best separable approximation on two-qutrit random density matrices. We combine the numerical results with theoretical methods in order to generate random representative families of positive partial transposed bound entangled (BE) states and analyze their properties. Our results are disclosing that for the two-qutrit system the BE states have negligible volume and that these form tiny `islands' sporadically distributed over the surface of the polytope of separable states. %We devise a method for estimating numerically the average thickness of these formations and their frequency of occurrence. The detected families of BE states are found to be located under a layer of pseudo one-copy undistillable negative partial transposed states with the latter covering the vast majority of the surface of the separable polytope.