The Safer Qubit Route Depends on Distance

Fault-tolerant semiconductor architectures may need to move logical qubits encoded across multiple spins. The authors model two-, three- and four-spin encodings under spatially and temporally correlated 1/f noise and derive fidelity and leakage for several shuttling protocols. Parallel motion generally protects short transfers best, while sequential motion wins at long range, with the crossover depending on device parameters. The analysis reduces prediction to a set of independently measurable pairwise dephasing factors. It is theoretical guidance rather than a device demonstration, but it connects trajectory choice directly to correlated noise and leakage.