Resisting high-energy impact events through gap engineering in superconducting qubit arrays

TL;DR

This paper demonstrates that gap engineering in superconducting qubit arrays effectively prevents correlated errors caused by high-energy impacts, enhancing fault tolerance in quantum computing.

Contribution

It introduces a novel gap engineering approach in superconducting qubits to resist high-energy impact-induced correlated errors, improving quantum error correction reliability.

Findings

Strong gap engineering prevents T1 degradation during impact events.

Weak gap engineering shows correlated T1 degradation under impact.

Strong gap engineered qubits are robust to optical QP poisoning.

Abstract

Quantum error correction (QEC) provides a practical path to fault-tolerant quantum computing through scaling to large qubit numbers, assuming that physical errors are sufficiently uncorrelated in time and space. In superconducting qubit arrays, high-energy impact events produce correlated errors, violating this key assumption. Following such an event, phonons with energy above the superconducting gap propagate throughout the device substrate, which in turn generate a temporary surge in quasiparticle (QP) density throughout the array. When these QPs tunnel across the qubits' Josephson junctions, they induce correlated errors. Engineering different superconducting gaps across the qubit's Josephson junctions provides a method to resist this form of QP tunneling. By fabricating all-aluminum transmon qubits with both strong and weak gap engineering on the same substrate, we observe starkly different responses during high-energy impact events. Strongly gap engineered qubits do not show any degradation in T1 during impact events, while weakly gap engineered qubits show events of correlated degradation in T1. We also show that strongly gap engineered qubits are robust to QP poisoning from increasing optical illumination intensity, whereas weakly gap engineered qubits display rapid degradation in coherence. Based on these results, gap engineering removes the threat of high-energy impacts to QEC in superconducting qubit arrays.