Relaxation Mechanisms of Transmon Qubits Far Detuned from Readout Resonators

Achieving long qubit relaxation times is crucial for implementations of quantum computing. The superconducting transmon is one of the leading quantum computing platforms, for which coherence time improvements have been approached through improvements in materials, defect engineering, and circuit design. We characterize and discuss the effects of resonator-qubit detuning on qubit performance in systems where qubit readout is and is not protected by a Purcell filter, exploring also the impact of different material systems. We further explore the influence of circuit design and readout parameters on both relaxation and dephasing. This work enriches our basic understanding of loss mechanisms in transmon qubits and circuits.