We construct a set of PPT (positive partial transpose) states and show that these PPT states are not separable, thus present a class of bound entangled quantum states.
@article{arxiv.quant-ph/0603105,
title = {A Class of Bound Entangled States},
author = {Shao-Ming Fei and Xianqing Li-Jost and Bao-Zhi Sun},
journal= {arXiv preprint arXiv:quant-ph/0603105},
year = {2009}
}