Quantum phenomena such as entanglement can improve fundamental limits on the sensitivity of a measurement probe. In optical interferometry, a probe consisting of N entangled photons provides up to a \(\sqrt{N}\) enhancement in phase sensitivity compared to a classical probe of the same energy. Here, we employ high-gain parametric down-conversion sources and photon-number-resolving detectors to perform interferometry with heralded quantum probes of sizes up to N = 8 (i.e. measuring up to 16-photon coincidences). Our probes are created by injecting heralded photon-number states into an interferometer, and in principle provide quantum-enhanced phase sensitivity even in the presence of significant optical loss. Our work paves the way toward quantum-enhanced interferometry using large entangled photonic states.

纠缠等量子现象可以改善测量探头灵敏度的基本限制。在光学干涉测量中，与相同能量的经典探针相比，由N 个纠缠光子组成的探针可在相位灵敏度方面提供高达\(\sqrt{N}\) 的增强。在这里，我们采用高增益参量下转换源和光子数分辨探测器来使用尺寸高达N  = 8 的量子探针（即测量多达 16 个光子重合）进行干涉测量。我们的探针是通过将预示的光子数状态注入干涉仪而创建的，原则上即使在存在显着光学损耗的情况下也能提供量子增强的相位灵敏度。我们的工作为使用大纠缠光子态的量子增强干涉测量铺平了道路。