Scientific Reports 6: Article number: 22027; published online: 23 February 2016; updated: 10 June 2016

In the original version of this Article, an additional affiliation for Lin Chen and YiMing Zhu was omitted. The correct affiliation is listed below:

Cooperative Innovation Center of Terahertz Science, Chengdu 611731, China.

This error has now been corrected in the PDF and HTML versions of the Article.