Stimulated spin noise in an activated crystal

Abstract

In the spin noise spectroscopy, the magnetic susceptibility spectrum is known to be provided by the spinsystem untouched by any external perturbation, or, better to say, disturbed only by its thermal bath. We propose a new version of the spin noise spectroscopy, with the detected magnetization (Faraday-rotation) noise being stimulated by an external fluctuating magnetic field with a quasi-white spectrum. Experimental study of the stimulated spin noise performed on a BaF 2 : U 3+ crystal in a longitudinal magnetic field has revealed specific features of this approach and allowed us to identify the Van-Vleck and population-related contributions to the AC susceptibility of the system and to discover unusual magnetic-field dependence of the longitudinal spin relaxation rate in low magnetic fields. It is shown that spectra of the stimulated and spontaneous spin noise, being both closely related to the spin-system magnetic susceptibility, are still essentially different. Distinctions between the two types of the spin-noise spectra and two approaches to the spin noise spectroscopy are discussed. arXiv:1906.12104v1 [cond-mat.mes-hall]

Nonlinear spectroscopy of high-spin fluctuations

“…We illustrate experimentally theoretical predictions taking Cs atomic vapour as testbed, because in this case the multiplet corresponding to the total spin S = 3, 4 is easily accessible by the spin noise spectroscopy [31,32]. The results presented in the work can open up a way for system sublevels optical control, which can be executed by combination with radiofrequency addressing of the states [33] or 'active' spin noise spectroscopy [34].…”

Theory of optically detected spin noise in nanosystems

“…In conclusion, we note that the direct measurement of the high order spin correlators is challenging, and a number of alternative detection methods are suggested. For example, to overcome the parametric suppression of the high order cumulants for many spins, one can study the "stimulated" spin noise [163], when external magnetic field [164] or optical orientation synchronizes single spins, so that they are no longer independent. The other possibility of high order spin noise measurement is due to the nonlinear relation between the detected Faraday rotation angle and the spin polarization.…”