This paper investigates the quickest change detection of quantum states in a universal setting: specifically, where the post-change quantum state is not known a priori. We establish the asymptotic optimality of a two-stage approach in terms of worst average delay to detection. The first stage employs block POVMs with classical outputs that preserve quantum relative entropy to arbitrary precision. The second stage leverages a recently proposed windowed-CUSUM algorithm that is known to be asymptotically optimal for quickest change detection with an unknown post-change distribution in the classical setting.

翻译：本文研究量子态在普适场景下的最快变点检测问题：具体而言，即变点后的量子态先验未知的情形。我们证明了一种两阶段方法在最坏平均检测延迟意义下的渐近最优性。第一阶段采用具有经典输出的块POVM测量，该测量能以任意精度保持量子相对熵。第二阶段利用最近提出的窗口化CUSUM算法，该算法在经典场景下对未知变点后分布的最快变点检测已被证明是渐近最优的。