Schmidt rank constraints in Quantum Information Theory

Abstract

Can vectors with low Schmidt rank form mutually unbiased bases? Can vectors with high Schmidt rank form positive under partial transpose states? In this work, we address these questions by presenting several new results related to Schmidt rank constraints and their compatibility with other properties. We provide an upper bound on the number of mutually unbiased bases of ${\mathbb{C}}^m\otimes {\mathbb{C}}^n$ $(m\le n)$ formed by vectors with low Schmidt rank. In particular, the number of mutually unbiased product bases of ${\mathbb{C}}^m\otimes {\mathbb{C}}^n$ cannot exceed $m+1$, which solves a conjecture proposed by McNulty et al. Then we show how to create a positive under partial transpose entangled state from any state supported on the antisymmetric space and how their Schmidt numbers are exactly related. Finally, we show that the Schmidt number of operator Schmidt rank 3 states of ${\mathcal{M}}_m\otimes {\mathcal{M}}_n(m\le n)$ that are invariant under left partial transpose cannot exceed $m-2$.

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