A system able to store several quantum states, with the ability to absorb and retrieve a given state on demand, is dubbed a Random-Access Quantum Memory. Such memories can be used in quantum repeaters to improve long-distance quantum communication, but also to provide an alternate parallelism strategy in quantum processors. This PhD project will be about demonstrating high-fidelity storage of microwave quantum states using an ensemble of rare-earth ion spins and interfacing it with a superconducting circuit. Our current challenge is to achieve strong, adjustable coupling between the spin and superconducting circuit—a pivotal aspect of our research. We will explore a new type of spin system that promises exceptional coherence at zero magnetic field and enhanced coupling strength. The internship will center on fabricating and measuring a test sample to evaluate the performance of this innovative system during the internship. The PhD thesis will center on developing and testing a complete hybrid quantum system able to store and retrieve quantum bits generated by a superconducting circuit into the spin ensemble. The internship will take place in the physics lab at ENS Lyon, in the quantum circuit group (http://physinfo.fr)