Simulating noise on a quantum processor: interactions between a qubit and resonant two-level system bath

Two-level system (TLS) defects are one of the limiting factors affecting qubit coherence. The two primary models for TLS behavior are the standard model, which describes the interactions of distributions of TLSs with continuous wave devices, and single TLS models. However, there is very little work exploring the experimentally observed intermediate range where countable numbers of TLSs interact with quantum devices. Our work closes the gap on this regime. We start with one million TLSs distributed around the surface of a qubit and pick the 200 highest coupled TLSs. We then perform a full Lindbladian simulation to analyze the effects of resonant TLSs defects on qubit energy relaxation times. We find that 150 of the strongest coupled TLSs are enough to accurately describe the qubit energy relaxation time. We show that T1 dropouts can occur due to a strongly coupled TLS as far as a few microns away from the junction. We then draw conclusions about TLS distribution limitations based on experimental observation.