We study sequential quantum changepoint detection in settings where the pre- and post-change regimes are specified through constraints on the expectation values of a finite set of observables. We consider an architecture with separate measurement and detection modules, and assume that the observables relevant to the detector are unknown to the measurement device. For this scenario, we introduce shadow-based sequential changepoint e-detection (eSCD), a novel protocol that combines a universal measurement strategy based on classical shadows with a nonparametric sequential test built on e-detectors. Classical shadows provide universality with respect to the detector's choice of observables, while the e-detector framework enables explicit control of the average run length (ARL) to false alarm. Under an ARL constraint, we establish finite-sample guarantees on the worst-case expected detection delay of eSCD. Numerical experiments validate the theory and demonstrate that eSCD achieves performance competitive with observable-specific measurement strategies, while retaining full measurement universality.

翻译：我们研究序贯量子变点检测问题，其中变点前后的状态通过有限组可观测量期望值的约束来刻画。我们考虑一种测量模块与检测模块分离的架构，并假设检测器相关的可观测量对测量设备而言是未知的。针对这一场景，我们提出基于影子的序贯e-变点检测（eSCD）协议——该创新方案将基于经典影子的通用测量策略与建立在e-检测器上的非参数序贯检验相结合。经典影子为检测器对观测量的选择提供了通用性，而e-检测器框架则能显式控制平均虚警运行长度（ARL）。在ARL约束条件下，我们建立了eSCD在最坏情况期望检测延迟上的有限样本保证。数值实验验证了理论结果，并证明eSCD在保持完全测量通用性的同时，其性能可与针对特定观测量的测量策略相媲美。