Implementing multi-qubit entanglement of two-level systems inside a superconducting phase qubit L. B. Yu, Z.-Y. Xue, Z. D. Wang, Y. Yu and S. L. Zhu Eur. Phys. J. D, 61 2 (2011) 499-505 Published online: 08 October 2010 DOI: 10.1140/epjd/e2010-00258-5