Given m bounded observables O1,…,Om on a d-dimensional system and copies of an unknown state ρ, estimate each Tr(Oiρ) to additive error ε. Can the quantum sample complexity match the classical rate O(log(m)/ε2), or is there a provable separation? The 2024 source cites an upper bound O(log2(m)log(d)/ε4). See the cited papers for normalization and success-probability conventions.