What does a surface-code decoder infer?

Question: After repeated syndrome extraction in a surface code, what is the decoder trying to infer? A) The exact microscopic cause of every physical error event B) A likely correction class consistent with the observed syndrome history C) The full quantum statevector of the logical qubit D) The exact eigenvalue of every nonlocal logical operator before correction Correct: B Explanation: The decoder receives syndrome changes over time and chooses a correction or correction class that is consistent and likely under the assumed noise model. It does not need to identify the exact physical error history if different histories are logically equivalent. Topic: advanced quantum computing / surface code / decoding