Fig. 2: Experimental observation of the non-reciprocity in hot atoms.

a The forward (red) and backward (blue) propagation transmission spectra as a function of the weak probe field detuning Δs at the temperature of 80 °C. b The forward (green) and backward (brown) coincidence counts for 300 s as a function of the delay time τ with a temporal bin width of 1 ns.