Enhancing Quantum Memories with Light-Matter Interference

Abstract: Future optical quantum technologies, including quantum networks and distributed quantum computing and sensing, demand efficient, broadband quantum memories. However, achieving high efficiencies in optical quantum memory protocols is a significant challenge, and typical methods to increase the efficiency can often introduce noise, reduce the bandwidth, or limit scalability. Here, we present a new approach to enhancing quantum memory protocols by leveraging constructive light-matter interference. We implement this method in a Raman quantum memory in warm Cesium vapor, and achieve a more than three-fold improvement in total efficiency reaching $(34.3\pm8.4)\%$, while retaining GHz-bandwidth operation and low noise levels. Numerical simulations predict that this approach can boost efficiencies in systems limited by atomic density, such as cold atomic ensembles, from $65\%$ to beyond $96\%$, while in warm atomic vapors it could reduce the laser intensity to reach a given efficiency by over an order-of-magnitude, and exceed $95\%$ total efficiency. Furthermore, we find that our method preserves the single-mode nature of the memory at significantly higher efficiencies. This new protocol is applicable to various memory architectures, paving the way toward scalable, efficient, low-noise, and high-bandwidth quantum memories.