Low-Overhead Defect-Adaptive Surface Code with Bandage-Like Super-Stabilizers

TL;DR

This paper introduces a low-overhead, automated method for adapting surface codes to defective quantum processors using bandage-like super-stabilizers, significantly reducing qubit overhead and improving code robustness.

Contribution

The paper proposes a novel defect-adaptive surface code approach utilizing bandage-like super-stabilizers to enhance fault tolerance with fewer qubits in defective quantum processors.

Findings

Reduces disabled qubits by one-third at 2% defect rate.

Increases average code distance by 63%.

Scales better with larger processors and higher defect rates.

Abstract

To make practical quantum algorithms work, large-scale quantum processors protected by error-correcting codes are required to resist noise and ensure reliable computational outcomes. However, a major challenge arises from defects in processor fabrication, as well as occasional losses or cosmic rays during the computing process, all of which can lead to qubit malfunctions and disrupt error-correcting codes' normal operations. In this context, we introduce an automatic adapter to implement the surface code on defective lattices. Unlike previous approaches, this adapter leverages newly proposed bandage-like super-stabilizers to save more qubits when defects are clustered, thus enhancing the code distance and reducing super-stabilizer weight. For instance, in comparison with earlier methods, with a code size of 27 and a random defect rate of 2\%, the disabled qubits decrease by $1/3$, and the average preserved code distance increases by 63\%. This demonstrates a significant reduction in overhead when handling defects using our approach, and this advantage amplifies with increasing processor size and defect rates. Our work presents a low-overhead, automated solution to the challenge of adapting the surface code to defects, an essential step towards scaling up the construction of large-scale quantum computers for practical applications.