Halma, a routing-based technique for defects mitigation in quantum error correction

Hardware defects are anticipated as we scale up quantum chips for large-scale computation and must be carefully addressed. In this work, we introduce Halma, a routing-based technique that effectively mitigates check qubit defects during surface code stabilizer measurements on topology-constrained quantum hardware, such as superconducting chips. Halma is both spatially local and temporally efficient, allowing for easy integration into the standard syndrome extraction circuit of the surface code. It introduces minimal noise, has relatively relaxed requirements for defect sparsity, and is fully compatible with the existing superstabilizer technique. Preliminary simulations show significant improvements over the superstabilizer approach in terms of logical error rates for qubits encoded in the surface code with defective check qubits.