Fig. 3. Leakage during the bit-flip code.

The growth in $∣2⟩$ population vs. stabilizer code length. The circuit is run for a number of rounds and terminated with a readout sensitive to $∣2⟩$ population. The experimental data are averaged over measure or data qubits and fitted to an exponential (dashed lines) to extract rates. Further data are included in Supplementary Note 3. The inset shows the 21 qubit chain as implemented on the Sycamore device.