The internship project takes place at the ENS Lyon Physics Laboratory. It offers the chance to build a random-access quantum memory, a device that stores several quantum states and releases any one of them on demand, a key ingredient for parallel quantum processing. Electron spin ensembles store microwave states about 100 times longer than superconducting qubits but are limited to below 10% efficiency, a challenge the project tackles using ytterbium ions in CaWO₄, which keep state-of-the-art coherence at high concentration and operate at zero magnetic field. The milestones are to test a new deposition technique that boosts spin–resonator coupling, then demonstrate storage of classical and quantum microwave fields at an efficiency close to 100%.