Quantum Spintronics with Silicon Carbide and Oxides

Optically active spin defects in semiconductors can be used as quantum bits for information processing and sensing technologies [1]. These spin qubits have a built-in spin-photon interface that emits in the visible, infrared, and telecom bands which is crucial for quantum networks, retain their quantum properties over millisecond timescales or longer, can be manipulated using a simple combination of light and microwave pulses and can be integrated into electronically active devices. We discuss recent advances in this area including the integration of single spin qubits into silicon carbide (SiC) devices, as well as oxides, and pathways to extend spin coherence times [2].

SiC offers a powerful technological platform, mature device integration, and broad compatibility with CMOS fabrication techniques. In particular, the neutral divacancy complex (VV0) has been isolated in SiC optoelectronic devices with lifetime limited single-photon emission [3] and enables strategies for addressing charge noise sensitivity. We can further improve the fundamental quantum properties of these defects through isotopic engineering of the local nuclear spin environment [4]. Combining all these elements make divacancy defects in SiC an ideal platform for integrated devices, with access to both excellent optical properties and long-lived nuclear spin memories.

In addition to exploring the physics of the neutral divacancy (VV0), we are engineering new defect-based spin qubits in SiC for quantum communication and networks. Transition metal ions such as vanadium have host-agnostic orbital structures and operate in the (near) telecom regime [5], and therefore could be naturally integrated into pre-existing telecommunications networks without the need for complicated frequency conversion schemes. With decreasing temperature, we observe a remarkable four-orders-of-magnitude increase in spin relaxation time [6] and identify the underlying relaxation mechanisms which involve a two-phonon Orbach process. These results position vanadium as a prime candidate for scalable quantum nodes in future quantum networks.

Integrating these findings, we present a qubit system Er3+: CeO2 (cerium dioxide) in a nuclear spin free environment for supporting long-lived spins with a telecom C-band spin-photon interface for applications in fiber-based quantum networks. We describe the electron spin coherence of Er3+ ions doped in CeO2 epitaxial films grown on Si substrates [7]. The reduced nuclear spin noise in the host yields an electron spin coherence of 0.66 μs in the isolated ion limit and a spin relaxation of 2.5 ms, all measured at T=3.6 K. These results indicate the potential of this system as a flexible platform for quantum communication.

[1] C. P. Anderson, D. D. Awschalom, Physics Today 76, 26 (2023).
[2] C.P. Anderson et al., Sci. Adv. 8, 5 (2022).
[3] C. P. Anderson, et al. Science, 366, 1225 (2019).
[4] A. Bourassa, et al. Nat. Mater. 19, 1319 (2020).
[5] G. Wolfowicz et al., Sci. Adv. 6, 18 (2020).
[6] J. Ahn et al., Phys. Rev. Appl., in press (2024); arXiv: 2405.16303
[7] J. Zhang et al., npj Quantum Information, in press (2024) ; arXiv : 2309.16785