Two key milestones for quantum computing companies are crossing the [[QEC threshold]] and reducing the [[QEC overhead]].  While each order-of-magnitude reduction in physical error rate reduces the overhead, **improving the physical fidelity beyond 99.9% yields diminishing returns.**  However, this 99.9% fidelity threshold has multiple caveats. For example, it must be consistent across qubits, stable over time, combined with reasonable measurements and resets, and have low ‘leakage’ rates (a type of noise), etc.   Hence, the picture is complex, and many companies claiming 99.9% fidelity on a single two-qubit gate are far from being QEC ready.  However, a quantum hardware company that has reached 99.9% fidelity would benefit from using a set of classical QEC technologies to reduce errors rather than prioritising continued fidelity improvements. This strategy would help reduce the cost-per-qubit and make the quantum computer more power efficient.