  We use a laser-driven single (In,Ga)As quantum dot (QD) in the dressed state
regime of resonance fluorescence ($T = 4$ K) to observe the four
$D_1$-transition lines of alkali atomic cesium ($Cs$) vapor at room
temperature. We tune the frequency of the dressing continuous-wave laser in the
vicinity of the bare QD resonance $\sim 335.116$ THz ($\sim 894.592$ nm) at
constant excitation power and thereby controllably tune the center and side
channel frequencies of the probe light, i.e. the Mollow triplet. Resonances
between individual QD Mollow triplet lines and the atomic hyperfine-split
transitions are clearly identified in the $Cs$ absorption spectrum. Our results
show that narrow-band (In,Ga)As QD resonance fluorescence (RF) is suitable to
optically address individual transitions of the $D_1$ quadruplet without
applying magnetic field or electric field tuning.
