The study develops two thermometry methods using the sensitivity of cavity emission to ion motion. Experiments with a single ¹³⁸Ba⁺ ion in a 230 μm fiber cavity give consistent temperatures with both methods. Analysis of the second-order correlation function shows that the method can cover temperatures from near the motional ground state to tens of millikelvin and distinguish motion at different frequencies.
Paper link: Physical Review Applied 24, 024037 (2025)