*Peter Udvarhelyi1,2, Roland Nagy3, Florian Kaiser3, Sang-Yun Lee4, Jörg Wrachtrup3, Adam Gali2,5
(1. Lorand Eotvos Univ.(Hungary), 2. Wigner Res. Centre for Physics(Hungary), 3. Univ. of Stuttgart(Germany), 4. Korea Inst. of Sci. and Tech.(Korea), 5. Budapest Univ. of Tech. and Economics(Hungary))