[1] Y. Wu and L. Deng, Phys. Rev. Lett. 93, 143904 (2004).

[2] Y. Wu, J. Saldana, and Y. F. Zhu, Phys. Rev. A 67, 013811 (2003).

[3] R. Wang, Y. Du, Y. Zhang, H. Zheng, Z. Nie, C. Li, Y. Li, J. Song, and M. Xiao, J. Opt. Soc. Am. B 26, 1710 (2009).

[4] Z. Zuo, J. Sun, X. Liu, Q. Jiang, G. Fu, L.-A, Wu, and P. Fu, Phys. Rev. Lett. 97, 193904 (2006).

[5] P.-Z. Z.-Q. Nie, Y.-P. Zhang, T. Jiang, Y.-G. Du, C.-L. Gan, J.-P. Song, and K.-Q. Lu, Chin. Phys. Lett. 24, 3420 (2007).

[6] C.-S. Li, W.-T. Yin, C.-Z. Yuan, M.-Z Shi, Y. Zhao, and Y.-P. Zhang, Chin. Phys. Lett. 27, 044209 (2010).

[7] C. Li, Y. Zhang, Z. Nie, Y. Du, R. Wang, J. Song, and M. Xiao, Phys. Rev. A 81, 033801 (2010).

[8] L. Jia, F. Zhang, M. Li, Y. Liu, and Z. Chen, Chin. Opt. Lett. 7, 617 (2009).

[9] Z. Chu, J. Liu, K. Wang, and J. Yao, Chin. Opt. Lett. 8, 697 (2010).

[10] S. E. Harris, Phys. Today 50, 36 (1997).

[11] H. Ling, Y. Li, and M. Xiao, Phys. Rev. A 53, 1014 (1996).

[12] B. Wang, Y. Han, J. Xiao, X. Yang, C. Xie, H. Wang, and M. Xiao, Opt. Lett. 31, 3647 (2006).

[13] C.-J. Zhu, A.-A. Senin, Z.-H. Lu, J. Gao, Y. Xiao, and J.-G. Eden, Phys. Rev A 72, 023811 (2005).

[14] W. C. Magno, R. B. Prandini, P. Nussenzveig, and S. S. Vianna, Phys. Rev. A 63, 063406 (2001).