Coherent optical and spin spectroscopy of nanoscale Pr3+ : Y2O3

We investigate the potential for optical quantum technologies of Pr3+: Y2O3 in the form of monodisperse
spherical nanoparticles. We measured optical inhomogeneous lines of 27 GHz and optical homogeneous
linewidths of 108 and 315 kHz in particles with 400- and 150-nm average diameters, respectively, for the
1D2(0) ↔ 3H4(0) transition at 1.4 K. Furthermore, ground-state and 1D2 excited-state hyperfine structures in
Y2O3 are here determined by spectral hole burning and modeled by complete Hamiltonian calculations. Groundstate spin transitions have energies of 5.99 and 10.42 MHz, for which we demonstrate spin inhomogeneous
linewidths of 42 and 45 kHz, respectively. Spin T2 up to 880 μs was obtained for the ±3/2 ↔ ±5/2 transition
at 10.42 MHz, a value which exceeds that of bulk Pr3+-doped crystals reported so far. These promising results
confirm nanoscale Pr3+: Y2O3 is a very appealing candidate to integrate quantum devices. In particular, we
discuss the possibility of using this material for realizing spin-photon interfaces emitting indistinguishable single
photons.