Probing the Temperature of Single Quantum Dots Confined in a Nanoparticle Ion Trap by Fluorescence Thermometry

A charged particle trapped in a temperature-controlled nanoparticle ion trap is subjected to various heating and cooling processes, but probing the particle temperature remains difficult. Here, we demonstrate a method to determine the temperature of a single trapped fluorescent CdSe/CdS quantum dot (QD) by measuring its temperature-dependent fluorescence spectrum after laser excitation at 532 nm. The QD’s mean fluorescence wavelength then yields the QD temperature using the empirical Varshni relation. We observe a linear correlation between the temperatures of the QD and ion trap with a slope of one and an offset of 113 K. These experimental results are in satisfactory agreement with a simple power balance model and provide detailed insight into the relevance of various heating and cooling processes acting on the trapped particles, with photoabsorption, fluorescence, and collisional cooling being the most significant ones.