2008 to Jan. 2009, supported by the China Scholarship Council (CSC), I visited School of Computer Science, Cardiff University, UK as a visiting scholar. Then, I worked as a Guest Researcher at the Information Technology Lab (ITL), National Institute of Standards and Technology (NIST), U.S. from Jul. 2009 to Jul. 2011. After that, I came back to China and worked as a postdoctoral researcher at ICST, Peking University, where I became an Assistant Professor in Jun. 2013 and was promoted to Associate Professor in Aug. 2015.