Surface-Code Quantum Error Correction for Molecular Tweezer Arrays: Encoding, Layout, and Correlated Noise
Polar molecules trapped in optical tweezer arrays offer a promising platform for quantum information processing, providing precise control and long-range interactions that enable high-fidelity gate operations. We investigate quantum error correction in this system and show the influence of underlying physical noise. A mapping is constructed from a molecular tweezer array onto a rotated surface code in which a single specification of the array, namely, which code qubits share a molecule and where those molecules are located, determines both the correlated erasure structure and the dipolar exchange graph. We compare molecular encodings with rotational qudit dimensions (D), two and four under heralded molecular loss, coherent dipolar exchange, and imperfect heralding. It is found that a D= 4 encoding with spatially dispersed pairing exhibits a finite distance crossing at approximately the same per molecule loss rate as D= 2, while using 48-49 % fewer molecules, at the cost of a 6-10 % increase in sub-threshold logical error. Fixing the encoding and varying only the spatial embedding produces substantially larger effects: pairing the two co-located qubits along a lattice direction yields a logical-sector asymmetry of approximately fifty times. Over the simulated distances (d = 5, 7, 9), the disfavoured sector shows little or no suppression of logical error with increasing code distance, whereas the favoured sector improves by a factor of 1.5-2.3. We also find that Pauli twirl of the exchange interaction overestimates the logical error rate, which we attribute to the excitation-conserving structure of the interaction. These results reveal that the spatial embedding of correlated loss units is an important design parameter for molecular architectures and that single-sector benchmarks may be insufficient when correlated loss has directional structure.