On a matrix equality involving partial transposition and its relation to the separability problem

TL;DR

This paper investigates a special matrix equality involving partial transposition, identifies conditions under which it holds, and explores its implications for the quantum separability problem, potentially aiding higher-dimensional quantum state analysis.

Contribution

It introduces specific conditions where the partial transposition matrix equality holds for 4x4 matrices and applies this to develop new separability criteria for quantum states.

Findings

Identified particular 4x4 matrices satisfying the partial transposition equality.

Derived separability conditions based on the matrix equality.

Suggested potential generalizations to higher-dimensional systems.

Abstract

In matrix theory, a well established relation $(AB)^{T}=B^{T}A^{T}$ holds for any two matrices $A$ and $B$ for which the product $AB$ is defined. Here $T$ denote the usual transposition. In this work, we explore the possibility of deriving the matrix equality $(AB)^{\Gamma}=A^{\Gamma}B^{\Gamma}$ for any $4 \times 4$ matrices $A$ and $B$, where $\Gamma$ denote the partial transposition. We found that, in general, $(AB)^{\Gamma}\neq A^{\Gamma}B^{\Gamma}$ holds for $4 \times 4$ matrices $A$ and $B$ but there exist particular set of $4 \times 4$ matrices for which $(AB)^{\Gamma}= A^{\Gamma}B^{\Gamma}$ holds. We have exploited this matrix equality to investigate the separability problem. Since it is possible to decompose the density matrices $\rho$ into two positive semi-definite matrices $A$ and $B$ so we are able to derive the separability condition for $\rho$ when $\rho^{\Gamma}=(AB)^{\Gamma}=A^{\Gamma}B^{\Gamma}$ holds. Due to the non-uniqueness property of the decomposition of the density matrix into two positive semi-definte matrices $A$ and $B$, there is a possibility to generalise the matrix equality for density matrices lives in higher dimension. These results may help in studying the separability problem for higher dimensional and multipartite system.