Bad Qubits — Learn Quantum by Doing

Multiple choice

In the three-qubit bit-flip code with logical states |0_L> = |000> and |1_L> = |111>, which physical operation implements the logical X gate (X_L) transversally?

Apply X to only the first physical qubit
Measure all three qubits and flip the majority value
Apply X to all three physical qubits, mapping |000> -> |111> and |111> -> |000>
Apply a Hadamard to all three physical qubits