Uninterrupted Charge-Parity Detection in Offset-Charge Sensitive Transmons

The performance of transmon-based processors can be limited by spatiotemporal-correlated quasiparticle-induced errors, a significant impediment to quantum error correction. Intentionally operating a transmon in an offset-charge-sensitive regime enables us to probe quasiparticle tunneling dynamics through detection of charge-parity jumps. However, extended monitoring of charge-parity is complicated by the presence of low-frequency charge noise, manifest as offset-charge jumps on the order of minutes. In this work, we apply an external offset-charge modulation and use a direct-dispersive readout scheme to continuously detect charge-parity jumps, uninterrupted by the presence of discrete offset-charge jumps. We use this technique to characterize the impact of gap engineering at the junction in suppressing quasiparticle tunneling and investigate spatiotemporal-correlated errors in an OCS transmon array by monitoring charge-parity transitions of such devices.