  The effects of a collection of classical two-level charge fluctuators on the
coherence of a dynamically-decoupled qubit are studied. Distinct dynamics are
found at different qubit working positions. Exact analytical formulae are
derived at pure dephasing and approximate solutions are found at the general
working position, for weakly- and strongly-coupled fluctuators. Analysis of
these solutions, combined with numerical simulations of the multiple random
telegraph processes, reveal the scaling of the noise with the number of
fluctuators and the number of control pulses, as well as dependence on other
parameters of the qubit-fluctuators system. These results can be used to
determine potential microscopic models for the charge environment by performing
noise spectroscopy.
