[1] Shanghai Normal Univ, Dept Phys, Shanghai 200234, Peoples R China
[2] China Three Gorges Univ, Coll Sci, Yichang 443002, Peoples R China
[3] Natl Univ Singapore, Ctr Quantum Technol, 2 Sci Dr 3, Singapore 117542, Singapore
[4] Natl Univ Singapore, Dept Phys, 2 Sci Dr 3, Singapore 117542, Singapore