PPT states of almost maximal Schmidt number

We construct PPT states on $\mathbb{C}^m \otimes\mathbb{C}^n$ that have Schmidt number asymptotically approaching the smaller local dimension. More specifically, we construct a PPT state with Schmidt number at least $\left\lceil \frac{m + n - ((m - n)^2 + 4(m + n - 1))^{1/2}}{2} \right\rceil.$ In the case of equal local dimensions ($m = n$), this becomes $n - \lfloor(2n - 1)^{1/2}\rfloor$, far exceeding the previous constructions which achieved $n/2 + O(1)$. In the case of unequal local dimensions, our result shows that there exists a PPT state on $\mathbb{C}^n \otimes \mathbb{C}^{3n-4}$ with Schmidt number at least $n-1$.

Source: arXiv:2609.11849v1 - http://arxiv.org/abs/2609.11849v1 PDF: https://arxiv.org/pdf/2609.11849v1 Original Link: http://arxiv.org/abs/2609.11849v1