Quantum error correction method and apparatus

Quantum error correction for a quantum computing system comprising a decoding system 102: receiving 214 an error syndrome representative of an error state of qubits 106; and sending 220 a signal to a control system 104 upon determining that a probability of successfully correcting the error state fails to satisfy a predetermined success criterion. The signal may indicate the probability of successfully correcting the error state. The control system determines 224 whether to modify a quantum computation being performed on the qubits, e.g. restarting or aborting. The determination is based on: an amount of remaining quantum computation; a count of how many signals have been received; determining a logical error probability value exceeding a predefined maximum. The decoding system also identifies a proposed correction operation based on the syndrome and sends it to the control system. Determining that the probability of successfully correcting the error state fails to satisfy the success criterion comprises identifying at the decoding system an ambiguous decoding scenario.