1. Memory Division, SAMSUNG Electronics, Hwasung 18448, Republic of Korea
2. Department of Physics, Chungnam National University, Daejeon 34134, Republic of Korea
3. Institute of Quantum System (IQS), Chungnam National University, Daejeon 34134, Republic of Korea
4. Advanced Instrumentation, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea