  Pre-fault tolerant quantum computers have already demonstrated the ability to
estimate observable values accurately, at a scale beyond brute-force classical
computation. This has been enabled by error mitigation techniques that often
rely on a representative model on the device noise. However, learning and
maintaining these models is complicated by fluctuations in the noise over
unpredictable time scales, for instance, arising from resonant interactions
between superconducting qubits and defect two-level systems (TLS). Such
interactions affect the stability and uniformity of device performance as a
whole, but also affect the noise model accuracy, leading to incorrect
observable estimation. Here, we experimentally demonstrate that tuning of the
qubit-TLS interactions helps reduce noise instabilities and consequently
enables more reliable error-mitigation performance. These experiments provide a
controlled platform for studying the performance of error mitigation in the
presence of quasi-static noise. We anticipate that the capabilities introduced
here will be crucial for the exploration of quantum applications on solid-state
processors at non-trivial scales.
