Narrow optical homogeneous linewidths in rare earth doped nanocrystals.

A homogeneous linewidth of 85.6±4.4  kHz is reported in 60 nm Eu3+ doped Y2O3 nanocrystals at 1.3 K. This linewidth was measured by two-pulse photon echoes on highly scattering powders using heterodyne detection. Spectral diffusion was also investigated by three-pulse photon echoes and resulted in a limited broadening of the homogenous linewidth of about 250 kHz over 120  μs. Compared to achievable Rabi frequencies, in the range of several MHz, these values show that rare earth doped nanocrystals can be useful for applications in optical quantum information processing.