Figure 13. Effect of spatial placement of erasure qubits in a \(d=7\) surface code. Color indicates correlation between logical error rate and presence of an erasure qubit at each location in the \(7 \times 7\) grid of data qubits. Correlations are shown for \(\bar Z\) (top), \(\bar X\) (middle) and combined (bottom) error rates. “Checkerboard” patterns are evident in \(\bar Z\) and \(\bar X\) data but disappear for combined data.