What is a global phase?

Question: Why does global phase usually not affect measurement results? A) Because it deletes the quantum state B) Because it creates a new qubit C) Because multiplying the entire quantum state by the same phase does not change measurement probabilities D) Because it forces every result to become 1 Correct: C Explanation: A global phase multiplies the entire state by the same complex factor. It does not change measurement probabilities, although relative phase between components can matter. Topic: quantum computing / phase / measurement