Group-IV - vacancy colour centres in diamond are very promising realizations of quantum bits for quantum communication and sensor applications. We have recently performed a systematic study on the magnetooptical properties of such neutral [1] and negative [2] colour centres (Si-, Ge-, Sn- and Pb-vacancy colour centres in diamond) by means of density functional theory calculations within the Born-Oppenheimer approximation and beyond. We have found that in such colour centres, the electronic and vibronic degrees of freedom strongly interact. The negative colour centres are exemplary e⊗E type Jahn-Teller systems, where a degenerate electronic “e” level couples to a degenerate “E” vibration mode localized around the impurity atom. The neutral colour centres have optically excited states governed by a different Jahn-Teller effect, with two localized holes coupled to a vibration mode, which provides a physical explanation for the optically forbidden excited state of the Si-vacancy colour centre. Our theoretical models agree well with the experimentally observed optical signals of group IV - vacancy coulour centres including their spin-orbit fine structure.

[1] G. Thiering,  A. Gali,. npj Computational Materials 5(1), 18 (2019)
[2] G. Thiering,  A. Gali, Phys. Rev. X,  8, 021063 (2018)