Interferometry is one of the most sensitive techniques available to test physical theories and make measurements. In particular, optical ring interferometers based on the Sagnac effect are commonly used to measure rotation, but their performance is constrained by the shot-noise limit. Employing quantum states of light allows for more sensitive optical phase measurements as compared to classical-light scenarios.

Key to their success is the use of a two-photon quantum N00N state, featuring two photons in a superposition of states, where both photons are in one state. These states are known to possess particularly high phase sensitivity, making them valuable for precise measurements in quantum interferometry. In this case, the states are created from the product state of horizontally and vertically polarized photon pairs centred at 1,546 nm and generated by spontaneous parametric down-conversion in a nonlinear optical crystal of poled KTiOPO₄.

干涉测量是可用于测试物理理论和进行测量的最灵敏的技术之一。特别是，基于萨尼亚克效应的光学环形干涉仪通常用于测量旋转，但其性能受到散粒噪声限制。与经典光场景相比，采用光的量子态可以实现更灵敏的光学相位测量。

他们成功的关键是使用双光子量子 N00N 态，其特点是两个光子处于状态叠加，其中两个光子都处于一种状态。众所周知，这些状态具有特别高的相位灵敏度，这使得它们对于量子干涉测量中的精确测量很有价值。在这种情况下，状态是由以 1,546 nm 为中心的水平和垂直偏振光子对的乘积状态创建的，并通过极化 KTiOPO ₄的非线性光学晶体中的自发参量下转换产生。