What does code degeneracy mean?

Question: In quantum error correction, what does degeneracy mean? A) Different physical errors can have the same action on the code space or produce the same syndrome-relevant effect B) A code has no stabilizer generators C) Every correctable error must have a unique syndrome D) Logical operators are forbidden from commuting with stabilizers Correct: A Explanation: Quantum codes can be degenerate: distinct physical error operators may differ by stabilizers and therefore act equivalently on encoded states. This makes decoding different from simply assigning a unique physical error to every syndrome. Topic: advanced quantum computing / quantum error correction / degeneracy