A big quantum job needs millions of qubits working together and checking each other's mistakes over and over. Diamond qubits don't need a freezer and fit on a chip smaller than a stamp, but each check is slow, so big jobs can take years. Make the reading faster and watch the time drop.

Each logical qubit is a d × d surface-code patch. The code distance d is the smallest odd number that keeps the total failure below 1%: n_L · steps · d · p_L(d) ≤ 0.01, with p_L(d) = A·Λ^(−(d+1)/2). One syndrome round takes preparation + four gates + readout, and each logical step takes d rounds.

A and Λ are fitted to Stim + PyMatching circuit-level simulations (d = 3, 5, 7) with NV noise: 0.3% link, 1% readout, 0.2% preparation, and idle error during readout; Λ is forced non-increasing in readout time. "Standard" uses depolarizing gate and idle noise (200,000 shots); the two "biased" models use native circuits from adamas.xzzx_native with gate noise biased toward Z (bias 100, assumed, not measured) and pure dephasing during readout (100,000 shots, worse memory basis). If NV noise is that biased, the standard code needs about twice the distance and the XZZX code restores the baseline (Figure 51). The NV Λ assumes a 0.3% link error that has not been demonstrated, while the superconducting reference uses the measured Λ = 2.14. Workloads are illustrative scales, not published algorithm counts. Chapter E10, Section E10.5.