1. Department of Physics, Photonic Device Physics Laboratory, Yonsei University, 50 Yonsei-ro Seodaemun-gu, Seoul 120-749, South Korea
2. Center for Quantum Information, Korea Institute of Science and Technology (KIST), Seoul 02792, South Korea
3. Department of Physics, Nonlinear Optical Material & Spectroscopy, Sogang University, 35 Baek-beom-ro, Seoul 04107, South Korea