Near-Perfect Broadband Quantum Memory Enabled by Intelligent Spin-Wave Compaction

Quantum memory, a pivotal hub in quantum information processing, is expected to achieve temporal storage and coherent manipulation of quantum states with memory efficiency exceeding 90% and quantum fidelity surpassing the noncloning 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 Letter, we break through these constraints by unveiling a Hankel transform spatiotemporal mapping for light-spin-wave conversion in quantum memory and proposing an intelligently light-manipulated strategy for spin wave compaction, which maximizes memory efficiency while suppressing excess noise. This strategy is experimentally demonstrated for a Raman quantum memory in warm ^{87}Rb atomic vapor with an efficiency up to 94.6±1% and a low noise level of only 0.026±0.012 photon per pulse. The unconditional fidelity reaches 98.91±0.1% with an average of 1.0 photon per pulse for a 17 ns input signal. Our results successfully demonstrate a practical benchmark for broadband quantum memory that may facilitate advancements in high-speed quantum networks, quantum state manipulation, and scalable quantum computation.