Microscopic bath effects on noise spectra in semiconductor quantum dot qubits

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 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.

Reference: Seongjin Ahn, S. Das Sarma, J. P. Kestner, arXiv:2007.03689