Resisting high-energy impact events through gap-engineering in superconducting qubit arrays
Abstract
Quantum error correction (QEC) provides a practical path to fault-tolerant quantum computing through scaling, assuming that physical errors are rare and 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) populations across 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 (gap-engineering) provides a new method to resist QP tunneling.
By fabricating all-aluminum transmon qubits with both strong and weak gap-engineering on the same substrate, we observe a starkly different responses during single high-energy impact events.
Weakly-gap-engineered qubits show high rates of correlated $T_1$ errors, while the strongly-gap-engineered qubits do not show any degradation in $T_1$.
We also show 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 resolves high-energy impacts as a serious threat to QEC using superconducting qubit arrays.
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) populations across 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 (gap-engineering) provides a new method to resist QP tunneling.
By fabricating all-aluminum transmon qubits with both strong and weak gap-engineering on the same substrate, we observe a starkly different responses during single high-energy impact events.
Weakly-gap-engineered qubits show high rates of correlated $T_1$ errors, while the strongly-gap-engineered qubits do not show any degradation in $T_1$.
We also show 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 resolves high-energy impacts as a serious threat to QEC using superconducting qubit arrays.
