Silicon spin qubits with implanted single donor ions*

Single group-V donors in isotopically-enriched silicon (²⁸Si) are strong qubit candidates due to their long spin coherence times [1], small footprints and compatibility with the microelectronics industry. The spin of both the donor electron and nucleus, our resources for storing quantum information, can be controlled and readout using surface nanoelectronics and coupled over a range of length scales. High spin nuclei, such as antimony (¹²³Sb), provide exciting opportunities for storing more quantum information, all electrical control [2] and exploring quantum chaos [3].

The most versatile method for introducing donors in Si is ion implantation, a foundational technique of the information technology industry that has already demonstrated the production of long-lived phosphorus (³¹P) donor qubits. To date, we have utilised timed implantation to randomly distribute roughly the desired number of donors in the region of interest of our Si chip. This has allowed us to explore one and two qubit systems, however, in order to produce the large-scale arrays of qubits required to run useful quantum algorithms, we require deterministic ion implantation, in which single donor ions are implanted into precise locations.

Our solution to deterministic implantation relies on implanting donor ions through a moveable nanostencil into desired locations within the Si substrate. We count in single donor ions by collecting the ion beam induced charge (IBIC) signal at biased detector electrodes. Recent work [4] has shown the excellent detection fidelity (99.85 %) of near-surface implanted single ³¹P ions using these IBIC detectors. This method enables arrays of donors to be fabricated in a step-and-repeat process. Our goal is to integrate these deterministically implanted donors with surface control and readout nanociruitry to produce arrays of donor spin qubits to realise the flip-flop qubit architecture [5].

[1] J. T. Muhonen et al., Nature Nano. 9, 986 (2014)

[2] S. Asaad et al., Nature 579, 205 (2020)

[3] V. Mourik et al., Phys. Rev. E 98, 042206 (2018)

[4]  A. M. Jakob et al., Adv. Mat. 34, 2103235 (2022)

[5] G. Tosi et al., Nature Comm. 8, 450 (2017)