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On the comparison of volumes of quantum states

This paper aims to study the $\a$-volume of $\cK$, an arbitrary subset of the set of $N\times N$ density matrices. The $\a$-volume is a generalization of the Hilbert-Schmidt volume and the volume induced by partial trace. We obtain two-side estimates for the $\a$-volume of $\cK$ in terms of its Hilbert-Schmidt volume. The analogous estimates between the Bures volume and the $\a$-volume are also established. We employ our results to obtain bounds for the $\a$-volume of the sets of separable quantum states and of states with positive partial transpose (PPT). Hence, our asymptotic results provide answers for questions listed on page 9 in \cite{K. Zyczkowski1998} for large $N$ in the sense of $\a$-volume. \vskip 3mm PACS numbers: 02.40.Ft, 03.65.Db, 03.65.Ud, 03.67.Mn