Sensitivity and heat penalty in all-optical quantum thermometry with Germanium-vacancy color centers in diamond

All-optical thermometry based on laser-driven photoluminescence (PL) of germanium–vacancy (GeV−) centers in diamond is quantified in terms of a trade-off between temperature sensitivity and laser-induced heating. We show that the noise-floor sensitivity ηT of the temperature readout from the GeV− PL return scales as (pΔt)−1/2 with the laser power p and detection time Δt, allowing the temperature uncertainty to be reduced by increasing p and Δt. This noise-floor reduction is, however, never penalty-free. Specifically, higher laser powers translate into higher temperatures of the diamond crystal. We demonstrate that the noise-floor as low as ηT = 37.5 mK/Hz can be achieved with the laser power set at p = 6.30 mW. We also show that a further reduction of ηT is possible at higher p. The experimental setting implemented in this study helps keep the level of heat released in a diamond crystal well below the typical level of microwave-induced heating in nitrogen-vacancy center-based thermometry, thus offering an advantageous approach for diamond-based thermometry in biological systems.