Explicit designs of spin chains for perfect quantum state transfer X. Q. Xi, J. B. Gong, T. Zhang, R. H. Yue and W. M. Liu Eur. Phys. J. D, 50 2 (2008) 193-199 Published online: 24 October 2008 DOI: 10.1140/epjd/e2008-00206-0