Brieger, RaphaelRaphaelBriegerHeinrich, MarkusMarkusHeinrichRoth, IngoIngoRothKliesch, MartinMartinKliesch2025-03-062025-03-062025-03-04Physical review letters 134: 090801 (2025)https://hdl.handle.net/11420/54662Expectation values of observables are routinely estimated using so-called classical shadows—the outcomes of randomized bases measurements on a repeatedly prepared quantum state. In order to trust the accuracy of shadow estimation in practice, it is crucial to understand the behavior of the estimators under realistic noise. In this Letter, we prove that any shadow estimation protocol involving Clifford unitaries is stable under gate-dependent noise for observables with bounded stabilizer norm—originally introduced in the context of simulating Clifford circuits. In contrast, we demonstrate with concrete examples that estimation of “magic” observables can lead to highly misleading results in the presence of miscalibration errors and a worst case bias scaling exponentially in the system size. We further find that so-called robust shadows, aiming at mitigating noise, can introduce a large bias in the presence of gate-dependent noise compared to unmitigated classical shadows. Nevertheless, we guarantee the functioning of robust shadows for a more general noise setting than in previous works. On a technical level, we identify average noise channels that affect shadow estimators and allow for a more fine-rained control of noise-induced biases.en0031-9007|||1079-71142025American Physical SocietyTechnology::600: TechnologyJournal Article10.1103/PhysRevLett.134.0908012310.19947Journal Article