We propose and demonstrate two cavity-assisted thermometry methods that exploit the sensitivity of cavity radiation to the position of the ion in the cavity mode to achieve highly sensitive temperature measurements. Our analysis allows us to determine the relative positions of the rf null and the cavity mode by the change of cavity emission at different positions of the ion in the cavity mode. By analyzing the second-order correlation function of the cavity emission, temperature measurements from near the motional ground state to over tens of millikelvin can be achieved and motion patterns of different frequencies can be characterized. We demonstrate our approach by measuring the temperature of a single ${}^{138}{\mathrm{Ba}}^{+}$ ion trapped in a fiber microcavity with a length of 230 $\text{μ}\mathrm{m}$ using both proposed methods, achieving comparable results.

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• Atoms, ions, & molecules in cavities
• Cavity quantum electrodynamics
• Light-matter interaction
• Quantum information with trapped ions
• Quantum sensing
• Optical microcavities
• Trapped ions
• Thermometry