Adam Gali Abstract

Adam Gali
Hungarian Academy of Sciences

"Optical excitations of nitrogen-vacancy center in diamond"

Abstract

The negatively charged nitrogen-vacancy (NV) defect in diamond is a leading candidate for realizing solid state spin qubits operating at room temperature. NV(-) has a high spin ground state with $M_S=0$ and $M_S=\pm 1$ sublevels. By applying appropriate excitation (typically wave length of 543nm) the excited electron decays selectively to the $M_S=0$ of the ground state. This is a very robust process which makes possible to read-out and set the electron spin state of single NV(-) defect optically. The most approved model for the selective decay of the excited electron is a hypothetic 3-level model where the electron is driven to a triplet excited state upon light exposure and cools down through an intermediate singlet state to the ground state.

It is well-known that similar processes can take place in atoms or molecules. In the case of atoms the spherical symmetry helps to unravel the position of energy levels and the transitions between them. NV(-) defect has much lower C$_{3v}$ symmetry and the position of energy levels cannot be derived from analytical solutions. However, it is highly critical to determine the electronic structure of NV(-) in detail for quantum bit or magnetometry applications.

Recent advances in methodology developments make possible to address this issue. We show that NV(-) defect in bulk diamond can be well modeled by supercell first principles calculations where beyond standard density functional calculations provide the electronic structure and excitation energies of NV(-) defect. We will show how these calculations could unravel the nature of NV(-) defect.

Recent experiments indicate that diamond host can play an important role in the excitation process of NV(-) driving NV(-) into a so-called dark state which is presumably the neutral NV defect. We show briefly that the properties of NV(-) and NV(0) are very different but NV(0) is still may be used as a qubit.