Effect of surface treatment on superconducting qubit coherence

A promising approach toward solid-state universal quantum computer relies on the use of frequency-tunable qubits to apply the necessary entangling gates. However, while the qubits are detuned from a flux insensitive point, they are susceptible to flux noise, causing rapid dephasing. Furthermore, weakly-coupled defects can resonantly interact with the qubit, leading to energy relaxation. Thus, these points of defect interaction must be avoided during operation, thereby exasperating the frequency crowding issue present in large qubit arrays.

Previous experiments indicate that surface adsorbates play a role in both flux noise and microwave dielectric loss. Here we explore the effect of UHV bake and UV irradiation surface treatments on qubit dephasing and energy relaxation. We describe the results of Ramsey-based measurement flux noise power spectral density and T1 swap spectroscopy for treated and untreated devices.