Entanglement Rényi α entropy

Abstract

We study the entanglement R\'enyi $\ensuremath{\alpha}$ entropy $(\mathrm{ER}\ensuremath{\alpha}\mathrm{E})$ as the measure of entanglement. Instead of a single quantity in standard entanglement quantification for a quantum state by using the von Neumann entropy for the well-accepted entanglement of formation (EoF), the $\mathrm{ER}\ensuremath{\alpha}\mathrm{E}$ gives a continuous spectrum parametrized by variable $\ensuremath{\alpha}$ as the entanglement measure, and it reduces to the standard EoF in the special case $\ensuremath{\alpha}\ensuremath{\rightarrow}1$. The $\mathrm{ER}\ensuremath{\alpha}\mathrm{E}$ provides more information in entanglement quantification and can be used, for example, to determine the convertibility of entangled states by local operations and classical communication. A series of results is obtained: (i) we show that the $\mathrm{ER}\ensuremath{\alpha}\mathrm{E}$ of two states, which can be mixed or pure, may be incomparable, in contrast to the fact that there always exists an order for the EoF of two states; (ii) similar to the case of EoF, we study in a fully analytical way the $\mathrm{ER}\ensuremath{\alpha}\mathrm{E}$ for arbitrary two-qubit states, the Werner states, and isotropic states in the general $d$ dimension; and (iii) we provide a proof of the previous conjecture for the analytical functional form of the EoF of isotropic states in the arbitrary $d$ dimension.