Impact of Surface Treatment on Magnetic Noise in Superconducting Qubits

Interfacial and surface defects contribute to 1/f magnetic flux noise, a major source of superconducting qubit dephasing. In this work, we investigate various UHV vacuum packaging approaches and in situ surface treatments aimed at reducing the density of magnetic defects in superconducting qubits. Additionally, we examine the dependence of flux noise power on qubit geometry. To quantify the 1/f flux noise, we employ single-shot Ramsey interferometry, allowing us to extract the power spectral density of flux fluctuations in the compound junction of the qubit.