Fig. 6: Schematic for example NV center control pulse sequence realizing time modulations in both the noise filter function F(t) and quench function η(t).
From: Intrinsic and induced quantum quenches for enhancing qubit-based quantum noise spectroscopy
As shown in Eqs. (38) and (39), this control sequence in turn enables reconstruction of spectral function \({{{{{{{\mathcal{J}}}}}}}}[\omega ]\). The control pulses are periodically structured as 2M repetitions of a base sequence (period T = tf/2M), so that F(t) and η(t) have period 2T = tf/M. The noise filter function F(t) encodes timings of the standard dynamical-decoupling π-pulses within the qubit subspace. In addition, we can further engineer a modulating quench function η(t) by periodically switching between qubit subspaces of {mz = 0, mz = − 1} and {mz = 0, mz = + 1} (see also Table 1). The corresponding time-dependent NV levels used as sensor qubit states during the protocol are illustrated in the bottom part of the schematic.
