A single atom emitting resonance fluorescence into a coherent beam, and its use for non-destructive atom thermometry

Using a far-off-resonance optical dipole trap, we place a single neutral $^{87}$Rb atom in a weak, atom-resonant coherent beam, while also strongly illuminating it from an orthogonal direction to produce resonance fluorescence. The atom-modified coherent beam is then collected and its photon statistics analyzed. We observe first-order interference that can increase or decrease the beam flux, depending on the relative phase of the coherent beam and resonance fluorescence. This confirms predictions of Goncalves et al. [Phys. Rev. A 104, 013724]. The interference visibility is also shown to be a sensitive, time-resolved, non-destructive thermometer: by fitting the resulting photon count distributions, we infer the center-of-mass localization of the atom within the trap. With $1200$ atoms and integration time of $80\mathrm{ms}$ per atom, we demonstrate temperature uncertainties of $4$ for $\sim 30 \mu\mathrm{K}$ temperatures at $\sim 200\mu\mathrm{s}$ time resolution.