Frames from Functional Calculus

We introduce frames generated by applying families of functions to a diagonal operator through functional calculus, with diagonal entries forming a Carleson interpolating sequence.

First, for separated spectra contained in a Stolz domain and an angular sector, we prove that systems of fractional operator powers remain frames whenever the step size satisfies the natural angular restriction.

This extends earlier results for positive real spectra and permits noninteger powers.

We also show that the angular restriction is sharp in general.

Second, we give an $\ell^2$-perturbation criterion for frames generated by more general continuous functions, assuming a density condition on a curve containing the spectrum.

The results broaden the class of structured frames available in dynamical sampling and related operator-orbit problems.