Observation of eight-wave mixing via electromagnetically induced transparencyZhenkun Wu, Chenzhi Yuan, Zhaoyang Zhang, Huaibin Zheng, Shuli Huo, Ruyi Zhang, Ruimin Wang and Yanpeng ZhangEPL, 94 6 (2011) 64005DOI: https://doi.org/10.1209/0295-5075/94/64005