Donor atoms in silicon are a versatile platform for experiments in quantum information processing, as

well as quantum foundations. The electron [1] and nuclear [2] spin of a 31 P donor were the first qubits

demonstrated in silicon, and went on to become among of the most coherent qubits in the solid state,

with coherence times exceeding 30 seconds [3], and quantum gate fidelities approaching 99.99% [4].

This talk will provide an overview of the strategies we are devising to scale up beyond singe, isolated

donors. Some of these methods have been already experimentally demonstrated, while others are in

progress.

Using magnetic resonance, we have demonstrated an exchange-based 2-qubit CROT gate for electron

spins [5], in a device where we implanted a high dose of ${}^{31}\text{P}$ donors. Future experiments will focus on

using deterministic, counted single-ion implantation, for which we have recently demonstrated the

capability to detect an individual ion with 99.85% confidence [6]. With nuclear spins, we have achieved

the landmark result of universal 1- and 2-qubit logic operations with >99% fidelity, and prepared a 3-

qubit GHZ entangled state with 92.5% fidelity [7]. We have also demonstrated the coherent electrical

control of an electron-nuclear flip-flop qubit [8], which will greatly facilitate the integration of single-atom

qubits in nanoelectronic devices.

Heavier donors possess a high nuclear spin quantum number and a nonzero electric quadrupole

moment. In the process of operating a single spin-$7/2$ ${}^{123}\text{Sb}$ nucleus, we (re)discovered the phenomenon

of nuclear electric resonance, and applied it for the first time to a single nuclear spin [9]. Encoding

quantum information in the larger Hilbert space of high-spin nuclei will enable interesting options for

logical qubit encoding and quantum error protection [10]. This “scaling up inwards” strategy, combined

with “scaling up outwards” via exchange interaction and electric dipole coupling, provides great flexibility

in the design of a blueprint large-scale donor-based quantum computer in silicon.

[1] J. Pla et al., Nature 489, 541 (2012)

[2] J. Pla et al., Nature 496, 334 (2013)

[3] J. Muhonen et al., Nature Nanotechnology 9, 986 (2014)

[4] J. Muhonen et al., J. Phys: Condens. Matter 27, 154205 (2015)

[5] M. Madzik et al., Nature Communications 12, 181 (2021)

[6] A. Jakob et al., Advanced Materials 34, 2270022 (2022)

[7] M. Madzik et al., Nature 601, 348 (2022)

[8] R. Savytskyy et al., arXiv:2022.04438 (2022)

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

[10] J. Gross, Phys. Rev. Lett. 127, 010504 (2021)