Detection of long-range coherence in driven hot atomic vapors by spin noise spectroscopy

Abstract

We study intriguing dynamical features of hot Rubidium atoms driven by two light fields. The fields resonantly drive multiple Zeeman states within two hyperfine levels, yielding a cascaded-^-like structure in the frequency space. A non-Hermitian Floquet tight-binding lattice with imaginary hopping between the nearest states effectively describes the coherence dynamics between Zeeman states within the ground hyperfine level. This emergent non-Hermitian dynamics is responsible for the generation of long-range coherence between the distant Zeeman states in the nonequilibrium steady state. By performing minimally invasive spin noise spectroscopy at strong driving intensity, we observe higher harmonic peaks in the coherent part of the power spectrum. Such sharp coherent peaks arise exclusively from long-range coherence between distant ground states via multiphoton transitions. Moreover, the peak amplitudes reveal an exponential decay of the coherence with increasing separation between the states.