Nanoscale systems possessing long-lived spins and the ability to coherently couple to light are highly demanded for quantum devices implementations. Several approaches, like NV centers in diamond, semiconductor quantum dots are intensively investigated in the field, where an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. In this context, chemically synthesized Eu3+ doped Y2O3 nanoparticles have demonstrated great potential for quantum technologies based on their narrow optical homogeneous linewidth, down to the 10 kHz level, and millisecond-long spin coherence time. Here, we investigate an alternative nanoscale material: Pr3+: Y2O3. We first determine the Pr3+ hyperfine structure in Y2O3 by spectral hole burning and then measure photon and spin echoes from nanoparticles down to 150 nm. Spin T2 up to 880 μs was obtained for the ±3/2↔±5/2 hyperfine transition at 10.42 MHz, a value which exceeds that of bulk Pr3+doped crystals so far reported. These promising results confirm nanoscale Pr3+:Y2O3 as a very appealing candidate to integrate quantum devices.
Rare earth (RE) doped crystals are promising materials for quantum information processing (QIP). In particular, Eu3+:Y2O3 bulk crystals present long optical coherent lifetimes (T2), a fundamental parameter for QIP. In this thesis, we investigated this system at the nanoscale, which could be used to build hybrid devices where RE are coupled to other quantum systems. This work focuses on the development of Eu3+: Y2O3 particles with sub-wavelength size and on the static and dynamical contributions to Eu3+ optical linewidth. Systems with different particle and crystallite sizes were prepared using homogeneous precipitation. Optical inhomogeneous linewidths were found to decrease with high temperature annealing and reached values close to those of bulk crystals, showing that low defect concentrations can be obtained. A quasi-linear correlation with Raman linewidths was also observed. T1 population decays were measured by fluorescence and found longer than in the bulk, in good agreement with a model based on an effective refractive index model. Optical T2 were investigated by photon echo (PE) and holeburning techniques. We observed a coherence lifetime of 7.1 µs at 1.7 K in a 0.5 % Eu3+ doped sample, the highest value reported for any nanocrystal. Temperature dependence and spectral diffusion studies indicate that structure fluctuations and spin flips dominate dephasing.
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 $^{1}D_{2}(0)\ensuremath{\leftrightarrow}^{3}H_{4}(0)$ 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. Ground-state 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 $880\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$ was obtained for the $\ifmmode\pm\else\textpm\fi{}3/2\ensuremath{\leftrightarrow}\ifmmode\pm\else\textpm\fi{}5/2$ 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.
Rare-earth dopants in solids are conducive of sharp optical transitions and long spin coherence at cryogenic temperatures. While superb coherences are routine in high-quality bulk crystals, the more versatile materials such as rare-earth doped nanoparticles and ceramics have suffered from excessive decoherence due to disorder. This work reports a surprisingly narrow linewidth of Er in Y
2O
3 ceramics made with industry-standard synthesis technique, putting it on par with the best single crystalline counterpart. The ultranarrow linewidth also helps clarify decoherence pathways within the matrix.