Figure 1: Correlated and uncorrelated spin fluctuations in inhomogeneously broadened QD ensembles.
(a) Illustrations depicting the inhomogeneously broadened absorption band of a QD ensemble (green line), along with the homogeneously broadened absorption and associated Faraday rotation spectra [α(ω) and θ(ω)] of two representative singly charged QDs in the ensemble (QDA and QDB). The probe laser that is shown is primarily sensitive to fluctuations of the spin in QDA, but not QDB. (b) Cartoon showing two probe lasers at photon energies ω1 and ω2. The dotted lines depict the Faraday rotation (FR) sensitivity of each laser to spin fluctuations in QDs at energy ω, which has the same functional form as θ(ω) (note that the probe lasers are not sensitive to spin noise from QDs exactly on resonance, because θ(ω) is an odd function). Here, the two lasers are well separated in energy (Δω≫γh), and therefore they are sensitive to different subsets of QDs, so that the FR noise on the two lasers [θ1(t) and θ2(t)] are largely uncorrelated in time. (c) The same, but for the case of small laser detuning (Δω≤γh). Here, the two lasers probe predominantly the same dots and FR noise is correlated, giving larger measured noise power ‹[θ1(t)+θ2(t)]2›.
