Real-time estimation of the optically detected magnetic resonance shift in diamond quantum thermometry toward biological applications

Real-time estimation protocols for the frequency shift of optically detected magnetic resonance (ODMR) of nitrogen-vacancy (NV) centers in nanodiamonds (NDs) are the key to the recent demonstrations of diamond quantum thermometry inside living animals. Here we analyze the estimation process in multipoint ODMR measurement techniques (3-, 4-, and 6-point methods) and quantify the amount of measurement artifact derived from the optical power-dependent ODMR spectral shape and instrumental errors of experimental hardware. We propose a practical approach to minimize the effect of these factors, which allows for measuring accurate temperatures of single ND during dynamic thermal events. Further, we discuss integration of noise filters, data estimation protocols, and possible artifacts for further developments in real-time temperature estimation. This study provides technical details regarding quantum diamond thermometry and analyzes the factors that may affect the temperature estimation in biological applications.