What does operating below a surface-code threshold imply?

Question: What is the operational meaning of demonstrating a surface-code memory below threshold? A) Increasing the code distance suppresses the logical error rate, provided the physical error process remains below the relevant threshold B) Every logical operation becomes error-free once the physical error rate is below one percent C) Syndrome measurements become unnecessary because errors are corrected passively D) The threshold guarantees exponential suppression under every decoder and every correlated noise model Correct: A Explanation: Below threshold, increasing the size or distance of the code should improve logical reliability rather than make it worse. The numerical threshold is not universal: it depends on the noise model, syndrome-extraction circuit, decoder, and implementation details. Topic: advanced quantum computing / surface code / fault tolerance