[1] Natl Taiwan Univ, Dept Phys, Taipei 106, Taiwan
[2] Sungkyunkwan Univ, Sch Informat & Commun Engn, Suwon 440746, South Korea
[3] Sungkyunkwan Univ, SAINT, Suwon 440746, South Korea
[4] Ind Technol Res Inst, Natl Measurement Lab, Ctr Measurement Stand, Hsinchu 300, Taiwan
[5] Natl Taiwan Univ, Ctr Theoret Sci, Taipei 106, Taiwan
[6] Univ Cambridge, Cavendish Lab, Cambridge CB3 OHE, England