Cross-correlation spin noise spectroscopy of heterogeneous interacting   spin systems
  We develop and apply a minimally invasive approach for characterization of inter-species spin interactions by detecting spin fluctuations alone. We consider a heterogeneous two-component spin ensemble in thermal equilibrium that interacts via binary exchange coupling, and we determine cross-correlations between the intrinsic spin fluctuations exhibited by the two species. Our theoretical predictions are experimentally confirmed using `two-color' optical spin noise spectroscopy on a mixture of interacting Rb and Cs alkali vapors. The results allow us to explore the rates of spin exchange and total spin relaxation under conditions of strict thermodynamic equilibrium. 
Dibyendu Roy, Luyi Yang, Scott A. Crooker, and Nikolai A. Sinitsyn
cond-mat.mes-hall quant-ph