Rare-earth based quantum memory

id="offer-description" class="ecl-u-type-heading-2 ecl-u-mt-none ecl-u-mb-l">Offer Description 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 [1]. Such devices are critical for applications such as quantum repeaters, parallel quantum processing, and high-precision measurements. While various platforms —such as atomic ensembles, superconducting circuits, and mechanical oscillators—have demonstrated quantum memory capabilities, they often face trade-offs between coherence time, capacity, and coupling strength. Ensembles of electron spins for microwave quantum state storage combines three advantages. 1) They can offer storage times longer by two orders of magnitude compared to superconducting qubits [2]. 2) They have a small footprint, and are compatible with superconducting qubits. 3) Protocols exist for storing multiple states into the same device, and can be used to reduce the number of required qubits for quantum algorithm [3]. However, current. spin ensemble memories suffer from low storage efficiency (<10%) due to a fundamental trade-off: high spin concentration enhances coupling to microwave circuits but reduces coherence. To overcome this, we propose exploring a novel spin system—ytterbium atoms embedded in CaWO₄—which maintains state-of-the-art coherence at much higher concentrations than previously studied systems [4]. Additionally, this system can operate at zero