  Quantum coherence control usually requires extremely low temperature
environments. Even for spins in diamond, a remarkable exception, the coherence
signal is lost as temperature approaches 700 K. Here we demonstrate quantum
coherence control of the electron spins of nitrogen-vacancy centers in
nanodiamonds at temperatures near 1000 K. The scheme is based on initialization
and readout of the spins at room temperature and control at high temperature,
which is enabled by pulse laser heating and rapid diffusion cooling of
nanodiamonds on amorphous carbon films. Using high-temperature spin control, we
observe the magnetic phase transition of a single nickel nanoparticle at about
615 K. This work enables nano-thermometry and nano-magnetometry in the
high-temperature regime.
