Investigation into Low Frequency Charge Noise Mechanisms in a Tantalum Transmon

Recent measurements of the low frequency charge noise environment of a tantalum transmon [1] revealed two unexpected results: a noise power spectral density approximately two orders of magnitude less than that found on comparable aluminum and niobium devices and the presence of preferred charge offsets.  In this work, we present our investigation into the material origins of the tantalum’s novel charge noise environment.  By repeating our measurements over a range of cryogenic temperatures, it is possible to discern two categorical sources of noise.  One type of charge noise event is temperature dependent and causes predominantly nearest-neighbor charge offset transitions.  The other is temperature independent and causes large charge offsets.  The temperature independent noise compares favorably to ionizing radiation events while temperature dependent noise is likely on-chip charge fluctuations which may be a function of tantalum’s uniquely uniform surface chemistry.