Microscopic bath effects on noise spectra in semiconductor quantum dot qubits
Seongjin Ahn, S. Das Sarma, J. P. Kestner
Abstract
When a system is thermally coupled to only a small part of a larger bath, statistical fluctuations of the temperature (more precisely, the internal energy) of this ``sub-bath'' around the mean temperature defined by the larger bath can become significant. We show that these temperature fluctuations generally give rise to $1/f$-like noise power spectral density from even a single two-level system. We extend these results to a distribution of fluctuators, finding the corresponding modification to the Dutta-Horn relation. Then we consider the specific situation of charge noise in silicon quantum dot qubits and show that recent experimental data [E. J. Connors et al., Phys. Rev. B 100, 165305 (2019)] can be modeled as arising from as few as two two-level fluctuators, and accounting for sub-bath size improves the quality of the fit.