Ultra-sensitive hybrid diamond nanothermometer

Abstract Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors because of 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, were demonstrated to have enhanced temperature sensitivity ($11{\rm{\,\,mK\,\,H}}{{\rm{z}}^{ - 1/2}}$) (Wang N, Liu G-Q and Leong W-H et al. Phys Rev X 2018; 8: 011042), but the sensitivity was limited by the large spectral broadening of ensemble spins in nanodiamonds. To overcome this limitation, here we show 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 demonstrate a temperature sensitivity of $76{\rm{\,\,\mu K\,\,H}}{{\rm{z}}^{ - 1/2}}$. This hybrid design enables detection of 2 mK temperature changes with temporal resolution of 5 ms. The ultra-sensitive nanothermometer offers a new tool to investigate thermal processes in nanoscale systems.