Fig. 1: Simulated third-order correlation spectra of different types of classical and quantum noises.
From: Quantum nonlinear spectroscopy of single nuclear spins
a The scheme of correlation measurement. A sensor spin is initially prepared in the state |x〉, then its z-component \({\hat{S}}_{z}\) is coupled to a classical noise B(t) or a quantum object by \(\hat{B}\left(t\right)\), and the measurements along eθ are correlated to determine the statistical moments, e.g., Sijk. b 2D spectra \(\widetilde{S}\big({\nu }_{{ij}},{\nu }_{{jk}}\big)\) of the third moment Sijk for a Gaussian noise (upper) and a random-phased AC field (lower). c 2D spectra of the third moment for a sensor coupled uniformly to N spin-1/2’s (N = 1, 2, 3, and 6).
