Abstract: There are still many great open questions in modern science, for example (i) how to build a large-scale quantum computer, (ii) how to understand the transition from quantum to classical behaviour, and (iii) reconciling quantum mechanics with general relativity. In this seminar, I will show what contributions can be given to these diverse fields by designing and operating silicon nanoscale devices that contain ion-implanted donor atoms, especially when they host a high-spin nucleus.

In quantum information science, the electron [1] and nuclear [2] spins of 31P donors in silicon represent some of the most performant qubits in the solid state, with exceptionally long coherence times [3], and 1- and 2-qubit gate fidelities exceeding 99% [4]. Great progress is being made to demonstrate robust scale-up strategies for such platform, including the development of deterministic single-ion implantation [5].

Moving to heavier donors such as 123Sb provides a larger Hilbert space (8 dimension in the nucleus alone, 16 when including the electron [6]) that can be used to encode logical qubits [7]. I will present fresh experimental data on creating and manipulating “Schroedinger cat” states [8] of the 123Sb nucleus [8], demonstrating the ability to perform the full range of SU(2) and SU(8) operations on the system.

The higher complexity, and the presence of an electric quadrupole interaction with the nucleus, opens the door to explorations of quantum chaos [9] and other fundamental questions in quantum mechanics.

The nuclear spin of 123Sb donors also couples to mechanical strain [10]. This can be exploited to design devices containing piezoelectric materials to coherently drive nuclear acoustic resonance [11]. Taken to the extreme, one can envisage reaching the strong-coupling regime between a single 123Sb nuclear spin and a macroscopic mechanical oscillator, with potential applications to the study of the quantum-classical transition caused by gravitational effects [12].