Quantum communication offers higher security compared to traditional encryption by virtue of the fundamental laws of Physics. But quantum states are fragile. To be able to send qubits across long distances without losing our data, quantum repeaters are required. In this work, we use defects in diamonds as a building block for quantum networks. One of the defects that is particularly useful for this application is the silicon vacancy. It is formed by a silicon atom sitting in between two missing carbon atoms in the diamond lattice. Specialized microscopes are built to illuminate diamonds with lasers and detect the light emitted from these defects. This allows us to read and write the state of the qubit with light. However, probing single atom-like defects is challenging and we are currently working on understanding the electronic structure of neutral silicon vacancies. Recently, we also reported a new silicon-related defect that emits in the telecom band – wavelengths for which optical fiber-based telecommunication networks have the least losses. We are further trying to introduce other atoms into diamonds to create new quantum defects with improved properties.