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：本文研究了通用场景下量子态的快速变化检测问题：即后变化量子态事先未知。我们建立了两阶段方法在平均最差检测时延下的渐近最优性。第一阶段采用具有经典输出的块状POVM，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CUSUM算法，该算法在经典场景下对后变化分布未知的快速变化检测具有渐近最优性。