发表机构
Newcastle University（纽卡斯尔大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究检验负Kirkwood-Dirac拟概率在相互作用自由测量中的优势，发现其仅重新分配信息，不提升每吸收光子的Fisher信息，直接透射最优，负性优势不累积。
AI 中文摘要
负的Kirkwood-Dirac拟概率被认为赋予了相互作用自由测量和后选择计量学的量子优势。我们在相互作用自由测量所设计用于的任务上检验了这一论断：学习关于一个样本的信息，同时让其吸收尽可能少的光。路径和输出的Kirkwood-Dirac分布给出了对弱样本的线性响应：其实部响应吸收，其虚部响应相位。对于纯单光子通过任意干涉仪一次，每个吸收光子的透射率Fisher信息是直接透射值减去虚部平方之和：没有任何干涉仪或读出方式能胜过直接透射。负性除了将信息集中在弱照明的输出中外，没有其他作用。Kirkwood-Dirac分布的虚部在这里依赖于输出基，而非样本，因此存在一个基使得每一项都是实数，这是最优的。单光子每个吸收光子获得的信息仅通过相位响应实现，对于光学线路，这需要厚或非均匀展宽的样本，或者通过多次通过而吸收未被计数时，如临界耦合谐振器所示。对于检测弱吸收体，负性提供了单次试验的优势，该优势不会在多次试验中累积；相反，当存在没有物体时暗的输出时，优势会累积，这种情况不需要负性。
英文摘要
Negative Kirkwood--Dirac quasiprobabilities are credited with the quantum advantage of interaction-free measurement and postselected metrology. We test that claim on the task interaction-free measurement was designed for: learning about a sample letting it absorb as little light as possible. The Kirkwood--Dirac distribution of path and output gives the linear response to a weak sample: its real part responds to absorption, its imaginary part to a phase. For a pure single photon passing once through any interferometer, the Fisher information about transmittance per absorbed photon is the direct-transmission value minus a sum of squared imaginary parts: no interferometer or readout beats direct transmission. Negativity plays no role beyond concentrating information in weakly lit outputs. The imaginary parts of the Kirkwood-Dirac distribution depend on the output basis here, not on the sample, so a basis exists in which every term is real, which is optimal. A single photon gains information per absorbed photon only through a phase response, which for an optical line needs a thick or inhomogeneously broadened sample, or through many passes when absorptions go uncounted, as shown by a critically coupled resonator. For detecting a weak absorber, negativity gives a single-shot advantage that does not accumulate over multiple trials; advantage instead accumulates when there are outputs which are dark without the object, a case which needs no negativity.
Comments17+10 pages, 6 figures
