Universal Sequential Changepoint Detection of Quantum Observables via Classical Shadows

2026-02-12

AI Summary

This work addresses the problem of real-time change-point detection for unknown posterior observables in quantum systems by proposing a decoupled architecture that separates measurement from detection. It leverages classical shadows to enable universal measurement of arbitrary observables and integrates a nonparametric sequential test based on the e-detector framework for change-point identification. This approach is the first to combine classical shadows with the e-detector methodology, offering provable control over the false alarm rate while guaranteeing worst-case detection delay under finite-sample regimes—all without sacrificing measurement universality. Numerical experiments demonstrate that the method achieves detection performance comparable to specialized measurement strategies, thereby combining theoretical rigor with practical flexibility.

Technology Category

• Machine Learning: Quantum Machine Learning
• Reasoning under Uncertainty: Sequential Decision Making
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Security and Privacy: Large-scale security measurements
• Economics, Online Markets and Human Computation: LLM based quality controls for crowd work
• Responsible Web: Human-perceived consequences of algorithmic deployment on the web

Abstract

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.

Problem

• quantum changepoint detection
• classical shadows
• sequential detection
• observable constraints
• universal measurement

Innovation

• classical shadows
• sequential changepoint detection
• e-detectors
• quantum observables
• universal measurement