This thesis focuses on the development of a quantum memory in Yb:YSO for the application in a quantum repeater protocol. The coherence properties of this material were studied for different doping concentrations to analyze the flip flop relaxation process. An increase of optical and spin coherence was also observed by utilizing broad spin-polarization techniques.

Using an AFC spin-wave storage protocol, proof of principle experiments were performed with a total storage bandwidth up to 100 MHz. Temporal multi-mode storage was achieved with up to 1250 non-classical modes simultaneously stored in the memory. Using the coherence properties of the spin state, storage times over 4 ms could be shown, while maintaining the multimode capacity.