数无约束量子传感
Number-unconstrained quantum sensing
摘要：
量子传感通常被描述为一个约束优化问题：使用有限数量的粒子最大化关于未知量的信息。包括引力波干涉仪和一些原子传感器在内的重要传感器似乎并不符合这一描述，因为粒子数没有外部约束。在这里，我们发展了粒子数不受约束的量子传感理论，并描述了最佳粒子数是如何从粒子与环境的竞争和粒子与粒子的相互作用中产生的。我们将该理论应用于光学探测的原子介质建模为一个共振，饱和吸收体，并观察到出现定义良好的有限最优没有外部约束。结果矛盾的一些期望，从数量约束的量子传感，并表明，探测与压缩光束可以提供一个大的灵敏度优势超过经典的策略，当每个粒子数优化。
英文摘要：
Quantum sensing is commonly described as a constrained optimization problem: maximize the information gained about an unknown quantity using a limited number of particles. Important sensors including gravitational-wave interferometers and some atomic sensors do not appear to fit this description, because there is no external constraint on particle number. Here we develop the theory of particle-number-unconstrained quantum sensing, and describe how optimal particle numbers emerge from the competition of particle-environment and particle-particle interactions. We apply the theory to optical probing of an atomic medium modeled as a resonant, saturable absorber, and observe the emergence of well-defined finite optima without external constraints. The results contradict some expectations from number-constrained quantum sensing, and show that probing with squeezed beams can give a large sensitivity advantage over classical strategies, when each is optimized for particle number.
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