Negative eigenvalues of partial transposition of arbitrary bipartite states

The partial transposition of a two-qubit state has at most one negative eigenvalue and all the eigenvalues lie in [-1/2,1]. In this Brief Report, we extend this result by Sanpera et al. [A. Sanpera, R. Tarrach and G. Vidal, Phys. Rev. A 58, 826 (1998)] to arbitrary bipartite states. We show that partial transposition of an $m\otimes n$ state can not have more than (m-1)(n-1) number of negative eigenvalues. Low-dimensional states have been studied to show the tightness of this result and explicit examples have been provided for $mn\le 9$. It is also shown that all the eigenvalues of partial transposition lie within [-1/2,1]. Some possible applications are also discussed.