[1] Tsinghua Univ, Key Lab Atom & Mol Nanosci, Beijing 100084, Peoples R China
[2] Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China
[3] Beijing Univ Posts & Telecommun, Sch Sci, Beijing 100876, Peoples R China
[4] Beijing Univ Posts & Telecommun, Key Lab Opt Commun & Lightwave Technol, Beijing 100876, Peoples R China
[5] Tsinghua Natl Lab Informat Sci & Technol, Beijing 100084, Peoples R China