Bad Qubits — Learn Quantum by Doing

Multiple choice

Minimum-weight perfect matching (MWPM) decodes a surface code by pairing up 'detection events'. For Z-type checks, how many detection events does a single X error on a bulk (interior) data qubit produce?

Two: it touches two neighbouring Z-checks, lighting both
Zero: a single bulk error is undetectable
One: only the nearest Z-check fires
Four: every adjacent check in all directions fires