  Carrier spins in semiconductor nanocrystals are promising candidates for
quantum information processing. Using a combination of time-resolved Faraday
rotation and photoluminescence spectroscopies, we demonstrate optical spin
polarization and coherent spin precession in colloidal CsPbBr3 nanocrystals
that persists up to room temperature. By suppressing the influence of
inhomogeneous hyperfine fields with a small applied magnetic field, we
demonstrate inhomogeneous hole transverse spin-dephasing times (T2*) that
approach the nanocrystal photoluminescence lifetime, such that nearly all
emitted photons derive from coherent hole spins. Thermally activated LO phonons
drive additional spin dephasing at elevated temperatures, but coherent spin
precession is still observed at room temperature. These data reveal several
major distinctions between spins in nanocrystalline and bulk CsPbBr3 and open
the door for using metal-halide perovskite nanocrystals in spin-based quantum
technologies.
