26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

The effects of strain and electric fields on the quadrupole tensor of an individual Sb donor in a silicon device

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Speaker

Evert Stolte (UNSW)

Description

The I=7/2 nuclear spin of a 123Sb donor in silicon forms an eight-level qudit which has demonstrated logical encoding of non-classical states [1]. In our nanoscale electronic devices, the nuclear quadrupole tensor provides the anharmonicity required for individual transition addressability. Further, voltage pulses on gates can modulate the quadrupole tensor, which can manifest as in-situ energy detuning or coherent nuclear electrical resonance driving (NER) localized at the donor site [2]. The strength and orientation of a donor’s quadrupole tensor depend on the local electric field gradient (EFG) at the nucleus, which arises from the strain shift to the silicon crystal field, and electric fields produced by voltage biases on gates or trapped charges [3]. The relative strengths of these terms have previously remained unclear.

In this project, we have measured the quadrupole splitting and NER Rabi rates as a function of magnetic field angle, to determine the full quadrupole tensor of multiple donors. Subsequently, we compare this with COMSOL modelling of the device that maps the strain — which originates from the thermal expansion of nanofabricated gates relative to the bulk — and the electrostatic environment. This allows us to elucidate the separate origins of the quadrupole splitting. Our results motivate device-design strategies for engineered quadrupole interactions, including the substitution of poly-silicon for aluminum gates to reduce fabrication-induced strain and intentionally strain-inducing capping structures for oriented electric field gradients.

[1] X. Yu et al., “Schrödinger cat states of a nuclear spin qudit in silicon,” Nat. Phys., vol.21, no.3, pp.362–367 (2025)
[2] S. Asaad et al., “Coherent electrical control of a single high-spin nucleus in silicon,” Nature, vol.579, no.7798, pp.205–209, (2020)
[3] L. A. O’Neill et al, “Engineering local strain for single-atom nuclear acoustic resonance in silicon,” Applied Physics Letters, vol.119, no.17, p.174001 (2021)