[1] Peking Univ, State Key Lab Mesoscop Phys, Beijing 100871, Peoples R China
[2] Peking Univ, Dept Phys, Beijing 100871, Peoples R China
[3] Univ Sci & Technol China, Key Lab Quantum Informat, Hefei 230026, Peoples R China
[4] Washington Univ, Dept Elect & Syst Engn, St Louis, MO 63130 USA