Bad Qubits — Learn Quantum by Doing

Multiple choice

For a fault-tolerant gadget built on a distance-3 code, what is the defining error-containment property ('one fault in, at most one error out')?

A single fault may cause any number of errors, provided the gadget computes the correct syndrome
A single fault anywhere inside the gadget causes at most one error on each encoded output block
A single fault inside the gadget always causes zero errors on the output blocks
Up to two faults inside the gadget cause at most one error on each output block