Recovery dynamics of a gap-engineered transmon after a quasiparticle burst

TL;DR

This study investigates how gap-engineered transmon qubits respond to quasiparticle bursts caused by ionizing radiation, revealing that gap engineering reduces burst detection but is limited by slow phonon thermalization.

Contribution

The paper demonstrates that gap engineering can significantly reduce quasiparticle burst detection in transmons, but thermalization delays limit its effectiveness.

Findings

Gap engineering reduces burst detection rate by a factor of five.

Quasiparticle thermalization is slower than expected, limiting mitigation.

Phonon thermalization delays impact qubit coherence recovery.

Abstract

Ionizing radiation impacts create bursts of quasiparticle density in superconducting qubits. These bursts temporarily degrade qubit coherence which can be detrimental for quantum error correction. Here, we experimentally resolve quasiparticle bursts in 3D gap-engineered transmon qubits by continuously monitoring qubit transitions. Gap engineering allows us to reduce the burst detection rate by a factor of five. This reduction falls four orders of magnitude short of that expected if the quasiparticles were to quickly thermalize to the cryostat temperature. We associate the limited effect of gap engineering with the slow thermalization of the phonons in our chips after the burst.