Stefan uses Nitrogen Vacancy (NV) defects in Diamonds as qubits and combines them with superconducting microwave cavities and superconducting qubits for building a hybrid quantum device. In making the analogue to a classical computer the NV defect can be imagined as the memory, the superconducting qubit as processor and the superconducting cavity as bus interfacing both of them.
NV centers are especially promising because they features long coherence times meaning long storage time and allow combining it with superconducting devices due to its unique nature. They also feature optical and microwave transitions allowing to build a quantum transducer. A device interfacing flying qubits (photons) and stationary qubits, (artificial atoms) needed in quantum repeater networks as well as quantum memories, making long range quantum communication possible.