What does magic-state distillation accomplish?

Question: Which statement most accurately describes magic-state distillation in a Clifford-based fault-tolerant architecture? A) It approximates a non-Clifford unitary through increasingly long sequences of physical Clifford gates B) It converts arbitrary mixed states into pure stabilizer states, which are then used as logical qubits C) It directly corrects coherent errors in a logical T gate without ancillary states or postselection D) It consumes multiple noisy non-stabilizer ancillas and, when their noise is below a protocol threshold, probabilistically produces fewer higher-fidelity magic states Correct: D Explanation: Stabilizer operations alone are not computationally universal. Magic-state distillation uses Clifford operations, Pauli measurements, error-detecting codes, and postselection to purify noisy non-stabilizer resources that can enable fault-tolerant non-Clifford gates. Topic: advanced quantum computing / magic-state distillation / fault tolerance