Characterizing Low-Frequency Qubit Noise

Fluctuations of the qubit frequencies are one major problems to overcome on way scalable quantum computers. Of particular importance fluctuations with a correlation time that exceeds decoherence due decay and dephasing by fast processes. The statistics can be characterized measuring correlators outcomes periodically repeated Ramsey measurements. We describe dynamics during measurements evaluate two-time correlator for noise from two-level systems two- three-time Gaussian noise. explicit expressions compared simulations. find that, even though generally significantly different, already ten mimic provided they symmetric. This is not case asymmetric systems.