Sub-MHz homogeneous linewidth in epitaxial Y2O3: Eu3+ thin film on silicon

Abstract

Thin films provide nanoscale confinement together with compatibility with photonic and microwave architectures, making them ideal candidates for chip-scale quantum devices. In this work, we propose a thin film fabrication approach yielding the epitaxial growth of Eu³⁺ doped Y₂O₃ on silicon. We combine two of the most prominent thin film deposition techniques: chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). We report sub-megahertz optical homogeneous linewidths up to 8 K for the Eu³⁺ dopants in the film, and lowest value of 270 kHz. This result constitutes a ten-fold improvement with respect to previous reports on the same material, opening promising perspectives for the development of scalable and compact quantum devices containing rare-earth ions.

Keywords: homogeneous linewidth; quantum technologies; rare-earth; thin film.

Figure 1:

Epitaxial Y₂O₃: Eu³⁺ thin film on Gd₂O₃/Si substrate. (a) Schematic view of the multilayer structure. (b) Y₂O₃: Eu³⁺ film surface morphology observed by scanning electron microscopy (SEM).

Figure 2:

High-resolution X-ray diffraction (XRD) investigations. (a) θ/2θ scan showing [111] out-of-plane orientation for the Y₂O₃:Eu³⁺ film. (b) Omega scan around one of the (222) diffraction peaks yielding a mosaicity of 0.6°. (c, d) Pole figures showing in-plane orientation corresponding to that of the substrate, further confirming epitaxial growth. The arrows indicate the position of the diffraction spots in the reciprocal space.

Figure 3:

Photoluminescence (PL) spectroscopy of Eu³⁺ ions in the Y₂O₃ thin film. (a) Room temperature PL spectrum showing several Eu³⁺ emission lines including the strong ⁵D₀ →⁷F₂ emission at 611 nm. (b) ⁵D₀ →⁷F₂ PL decay recorded at 50 mK and 611 nm under resonant ⁷F₀ →⁵D₀ excitation at 580.79 nm. The dashed orange line corresponds to a single exponential fit to the data yielding a population lifetime T ₁ = 0.95 ms for the ⁵D₀ excited state.

Figure 4:

High resolution and coherent optical characterizations at mK temperature. (a) Inhomogeneous linewidth for the ⁵D₀ →⁷F₀ transition measured at three different excitation powers by scanning the excitation wavelength while monitoring the ⁵D₀ →⁷F₂ emission at 611 nm. A Gaussian curve fit to the data yields a full width at half maximum (FWHM) of 132 ± 5 GHz. The stars indicate spectral position within the linewidth of the ions probed in (c). (b) Spectral hole burned at 580.787 nm at a temperature of 800 mK (blue solid line). The dashed orange line correspond to a Lorentzian curve fit to the data yielding a hole width of 1.3 ± 0.4 MHz. (c) Homogeneous linewidth (left axis) and hole width (right axis) as a function of burn power measured at three different frequencies within the inhomogeneous line (see (a)). (d) Homogeneous linewidth as a function temperature (blue points). The dashed orange line corresponds to a fit to these data using eq. (1).