Four-Wave Mixing at peV Energy Scales

TL;DR

This paper reports measurements of third-order magnetic susceptibility in a disordered quantum Ising magnet, demonstrating four-wave mixing at extremely low energy scales (~peV) and exploring its temperature and field dependence.

Contribution

It provides the first experimental observation of four-wave mixing at peV energy scales in a quantum magnetic system, revealing insights into coherent spin dynamics.

Findings

$ ext{Re} \, ilde{eta}( u)$ follows a $rac{1}{T}$ dependence.

$ ext{Im} \, ilde{eta}( u)$ exhibits a high-temperature cutoff linked to dissipation.

$ ilde{eta}( u)$ decreases with transverse field, approaching a constant offset.

Abstract

We measure the non-linear magnetic susceptibility $\chi^{(3)}$ of the disordered quantum Ising magnet, \lihofour, and demonstrate four-wave mixing due to coherent (anti-)Stokes Raman scattering at $\sim$ 100 Hz (p$e$V) energy scales. The temperature dependence of $\chi^{(3)}$ approximately follows a $\frac{1}{T}$ form, with a high-$T$ cutoff that can be linked to dissipation in the coherent spin clusters. $\chi^{(3)}$ also decreases monotonically with a transverse field, approaching a constant offset above a few kOe, suggesting the presence of both coherent, and spontaneous Raman scattering.