This work was supported by the National Basic Research Program of China with Grant 2012CB315801, the National Natural Science Foundation of China (NSFC) with Grants 61133015 and 61272473, the National High-tech R&D Program of China with Grant 2013AA013501, and by the Strategic Priority Research Program of CAS with Grant X-DA06010303. The work was also supported by the EC EINS and EPSRC IU-ATC projects
