发表机构
Department of Physics and Astronomy, University of California Los Angeles; Challenge Institute for Quantum Computation, University of California Los Angeles; Center for Quantum Science and Engineering, University of California Los Angeles（加州大学洛杉矶分校物理与天文系; 加州大学洛杉矶分校挑战量子计算研究所; 加州大学洛杉矶分校量子科学与工程中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过将Fock态增强嵌入Qdyne协议，在捕获离子中实现了持久量子增强频率传感，精度随T^{-3/2}标度提升，增益达7.1dB，远超退相干极限。
AI 中文摘要
量子传感利用非经典态来提高测量灵敏度，但提供计量增益的同一态也会更快地退相干。这限制了可用的询问时间，并在实践中常常阻碍最终灵敏度的提高——因此，实际实现的有用量子优势一直很少见。在此，我们通过在量子外差（Qdyne）协议中嵌入Fock态增强来恢复持久的量子优势，将灵敏度与退相干限制的询问时间τ解耦。测量在量子增强增益最佳的短τ下进行，而精度随总测量时间累积。在捕获的40Ca+离子的运动模式上演示，我们观察到量子增强精度持续到超出退相干极限七个数量级的测量时间，标度为T^{-3/2}，且没有饱和迹象。使用n=3的Fock态，我们相对于86MHz载波达到0.5uHz的频率精度，实现约6x10^{-15}的分数精度。这相对于n=0态实现了7.1(10) dB的量子增强增益，与Fisher信息预测一致。这是Qdyne在固态自旋缺陷之外的首次演示。此外，通过使用量子谐振子进行频率混合，我们将操作扩展到1GHz以上，比脉冲动力学去耦实现的上限高出两个数量级。这些结果在提高最终灵敏度所需的长时间尺度上恢复了量子优势，对纳米级NMR和量子逻辑光谱学具有直接影响。
英文摘要
Quantum sensing uses nonclassical states to improve measurement sensitivity, but the same states that provide metrological gain also decohere more rapidly. This limits the usable interrogation time and, in practice, often precludes improvement in ultimate sensitivity - realized useful quantum advantage has consequently remained rare. Here, we restore persistent quantum advantage by embedding Fock-state enhancement within a quantum heterodyne (Qdyne) protocol, decoupling sensitivity from the decoherence-limited interrogation time τ. Measurements are acquired at short τ where the quantum-enhanced gain is optimal, while precision accumulates with the total measurement time. Demonstrated on the motional mode of a trapped 40Ca+ ion, we observe quantum-enhanced precision that persists to measurement times seven orders of magnitude beyond the dephasing limit, scaling as T^{-3/2} with no indication of saturation. Using the n=3 Fock state, we reach a frequency precision of 0.5uHz relative to an 86MHz carrier, achieving a fractional precision ~6x10^{-15}. This represents a quantum-enhanced gain of 7.1(10) dB over the n=0 state, in agreement with Fisher information predictions. This is the first demonstration of Qdyne beyond solid-state spin-defects. Further, by using the quantum harmonic oscillator to perform frequency mixing, we extend operation beyond 1GHz, two orders of magnitude above the ceiling of pulsed dynamical-decoupling implementations. These results recover quantum advantage at the long timescales required to improve ultimate sensitivity, with direct implications for nanoscale NMR and quantum logic spectroscopy.
