The reliable measurement of temperature is vital in a very wide range of scientific and industrial settings. Current generation thermometers all drift in their output with use. Our aim is to develop the next generation of temperature sensors that are driftless, able to measure temperatures reliably with low uncertainties over decadal timescales. In this PhD project you will help develop this solution based on a practical optically based thermometer using Doppler-broadening in an atomic vapour to provide primary (calibration-free) in-situ, traceable temperature measurements. We will work to miniaturise the thermometer to centimetre-scale, with a target of sub 0.1 kelvin accuracy across 300–500 K with the longer term-goal of developing the sensors into practical thermometers with similar form factors to, and as a viable alternative for, current temperature sensors to enable more efficient industrial processes, reducing energy use, and advancing digital, autonomous temperature traceability.