Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors for their long spin coherence time under ambient conditions. However, their spin resonances are relatively insensitive to non-magnetic parameters such as temperature. A magnetic-nanoparticle-nanodiamond hybrid thermometer, where the temperature change is converted to the magnetic field variation near the Curie temperature, was demonstrated to have enhanced temperature sensitivity (11 mK Hz^{-1/2}) [Phys. Rev. X 8, 011042 (2018)], but the sensitivity was limited by the large spectral broadening of ensemble spins in nanodiamonds. To overcome this limitation, here we showed an improved design of a hybrid nanothermometer using a single NV center in a diamond nanopillar coupled with a single magnetic nanoparticle of copper-nickel alloy, and demonstrated a temperature sensitivity of 76 uK Hz^{-1/2}. This hybrid design enabled detection of 2 millikelvins temperature changes with temporal resolution of 5 milliseconds. The ultra-sensitive nanothermometer offers a new tool to investigate thermal processes in nanoscale systems.
@article{arxiv.1912.12097,
title = {Ultra-sensitive hybrid diamond nanothermometer},
author = {Chu-Feng Liu and Weng-Hang Leong and Kangwei Xia and Xi Feng and Amit Finkler and Andrej Denisenko and Jörg Wrachtrup and Quan Li and Ren-Bao Liu},
journal= {arXiv preprint arXiv:1912.12097},
year = {2019}
}