Optical Spin-Photon Interfaces with a Focus on Transition Metal Defects in Silicon Carbide

Abstract

The conversion between stationary and flying qubits is a pillar of numerous quantum technologies such as distributed quantum computing as well as many quantum internet and networking protocols. These quantum technologies promise to use resources, in particular entanglement, not available to classical devices to accomplish tasks that are difficult or even impossible to realize with classical devices. Applications range from fundamental research to secure communication. Because some of these applications require the generation of entanglement, even over large distances, there is substantial interest in efficient interfaces between flying qubits, usually photons, and a stationary memory. In this thesis, we evaluate key aspects of optical spin-photon interfaces, a class of devices combining a stationary qubit memory (spins) and an interface with flying qubits (photons). We focus on defects in silicon carbide (SiC) in which a transition metal (TM) atom substitutes a silicon (Si) atom in the lattice, so that the energy levels with naturally bound quantum states localized around the defect lie within the band gap of SiC. We highlight two key properties of these defects as stationary-flying interconnects: First, they have favorable spin coherence properties and the pertaining nuclear spin of the TM can be used as a quantum memory. Second, they feature a localized and efficient spin-photon interface via their excited states. Defects where vanadium takes the place of a Si atom even allow for photon emission with frequencies in one of the fiber-optic transmission windows, which support efficient transmission in optical fiber. Our results are readily combined with numerical ab-initio and experimental data, providing intuition and further insight into the underlying physics. Additionally, the theoretical assessments of this thesis bridge the gap between the fundamental characterization of TM defects in SiC and their use as spin-photon interfaces in future experiments and quantum technology applications. For instance, the proposed nuclear-spin preparation protocol and spin control mark the first step towards an all-optically controlled integrated platform for quantum technology with TM defects in SiC.