Optical spin properties of Ce³⁺ centers in thin-film MgAl₂O₄

Recently, we have investigated the polarization dependence of Ce³⁺ centers in bulk spinel (MgAl₂O₄)[1], which can be utilized as a new class of solid-state spin qubits. Since the performance of the solid-state spin qubits depends on the host material properties [2-4], here, we investigate Ce³⁺ spin centers in thin-film spinel.

We deposit 100-nm-thick spinel films on MgO (001) substrate using rf magnetron sputtering. Subsequently, Ce ions are implanted into the film as well as a bulk spinel substrate as a reference with an implantation dose and power of 1.0×10¹⁴ cm^-2 and 45 keV, respectively.

We measure polarization-dependent photoluminescence (PL) excited by a polarized 325 nm laser. In the thin-film (bulk) sample, the change in the degree of circular polarization reaches ~2% (< 1%) under 50 mT at 20 K, suggesting more efficient spin-dependent PL in the film than the bulk. This may be due to the difference in the Ce³⁺ site’s symmetry, and implies the feasibility of optical initialization and readout of the Ce³⁺ spin-qubit state in oxides.

 

[1] M. Kawahara et al., Appl. Phys. Express 17, 072004 (2024).

[2] P. Neumann et al., Science 320, 5881 (2008).

[3] W. F. Kohel et al., Nature 479, 84 (2011).

[4] S. Kanai et al., PNAS., 119, e2121808119 (2022).