Near-perfect broadband quantum memory enabled by intelligent spinwave compaction

Abstract: Quantum memory, a pivotal hub in quantum information processing, is expected to achieve high-performance storage and coherent manipulation of quantum states, with memory efficiency exceeding 90% and quantum fidelity surpassing the non-cloning limit. However, the current performance falls short of these requirements due to the inherent trade-off between memory efficiency enhancement and noise amplification, which not only imposes significant demands on quantum purification but also fundamentally impedes continuous-variable quantum information processing. In this paper, we break through these constraints, enabling high-performance quantum memory and unlocking new possibilities for quantum technologies. We unveil a Hankel-transform spatiotemporal mapping for light-spinwave conversion in quantum memory, and propose an intelligent light-manipulated strategy for adaptive spinwave compaction, which can maximize the conversion efficiency and simultaneously suppress the excess noise. This strategy is experimentally demonstrated for a Raman quantum memory in warm 87Rb atomic vapor with an efficiency up to 94.6% and a low noise level of only 0.026 photons/pulse. The unconditional fidelity reaches 98.91% with an average of 1.0 photons/pulse for a 17-ns input signal. Our results successfully demonstrate a practical benchmark for broadband quantum memory, which may facilitate advancements in high-speed quantum networks, quantum state manipulation, and scalable quantum computation.