Ab Initio Magneto-Optical Spectrum of Group-IV Vacancy Color Centers in Diamond

Abstract

Group-IV vacancy color centers in diamond are fast emerging qubits that can be harnessed in quantum communication and sensor applications. There is an immediate quest for understanding their magneto-optical properties, in order to select the appropriate qubits for varying needs of particular quantum applications. Here we present results from cutting-edge ab initio calculations about the charge state stability, zero-phonon-line energies, and spin-orbit and electron-phonon couplings for group-IV vacancy color centers. Based on the analysis of our results, we develop a novel spin Hamiltonian for these qubits which incorporates the interaction of the electron spin and orbit coupled with phonons beyond perturbation theory. Our results are in good agreement with previous data and predict a new defect for qubit applications with thermally initialized ground state spin and long spin coherence time.

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Plain Language Summary

Future quantum communication networks could revolutionize the secure communication and cryptography of the global socioeconomical system. These networks require solid-state sources of single photons whose spin properties can be read and manipulated. A leading candidate for such a source is a type of defect in diamond known as a silicon-vacancy center, in which two neighboring carbon atoms are replaced by one silicon atom. However, the spin properties constrain its operation to extremely low temperatures, which requires expensive cooling systems that are not practical for proposed quantum technology applications. Here, we theoretically investigate replacing silicon with other elements from the same column in the periodic table.

We use density-functional theory calculations to see if other group-IV elements—namely, germanium, tin, and lead—in a vacancy center exhibit similar optical properties to silicon but with improved spin properties that permit an economical cooling system. We develop a new theory for understanding the interaction of light and magnetic fields with these color centers, and we explore how the dynamical motion of the atoms strongly affects the magneto-optical properties of the color center. By combining our theory with density-functional theory calculations, we find that lead-vacancy color centers should have favorable optical and spin properties for operating at room temperature. Tin-vacancy centers could also work at practical (though less convenient) cryogenic temperatures.

Our results imply that a solid-state single-photon source with an optically addressable well-behaved spin can be realized under convenient experimental conditions. Our theory paves the way for exploring solid-state single-photon sources in other 3D and 2D materials in the near future.