Cavity-enhanced efficient optical quantum memory for multiplexed entanglement distribution

Recent breakthroughs in quantum technologies combining academic and R&D efforts have ushered quantum networks into a new era, where quantum information can be stored, processed, and transferred. A key challenge in this new era is enhancing the capabilities of individual nodes to realize a quantum repeater that will extend quantum links to reach continental distances. Quantum memories are one of the building blocks for synchronizing temporal events in a quantum repeater, allowing entanglement distribution beyond the physical limitations of fiber loss. In this context, our proposed research seeks to push the boundaries of quantum communication by developing a cutting-edge quantum memory designed for high-rate, long-distance entanglement distribution. The project focuses on the development of an efficient, multiplexed, cavity-enhanced quantum memory using a praseodymium (Pr3+)-doped yttrium orthosilicate (YSO) crystal, known for its long coherence times and multiplexing capabilities. The first objective is to demonstrate a cavity-enhanced on-demand quantum memory for single photons, using the spin-wave atomic frequency comb protocol. The challenge is to mitigate optical loss and noise to enable single-photon storage with a high signal-to-noise ratio. The second objective aims at implementing a novel spatial multiplexing scheme that leverages non-trivial collective spin excitations in the cavity memory. This will be combined with temporal and frequency multiplexing to enhance the memory's capacity to store multiple degrees of freedom. The ultimate goal is to distribute light-matter entanglement using cavity-enhanced multimode quantum memory over a 50 km deployed optical fiber in a metropolitan area. Our approach seeks to achieve higher efficiency and increased rates, which are essential for practical metropolitan quantum networks. These milestones are important steps toward building a robust application-ready quantum network and establishing a European quantum internet.