Evidence of two-coupled high-spin nuclei in silicon

High-dimensional quantum systems are desirable as they can be used to encode logical qubits that can be error corrected. Sb donor qudit devices is an excellent candidate for such purposes where the full control within its 16-dimensional Hilbert space has been recently demonstrated [Xi Yu et al. arXiv:2405.15494 (2024)]. Here, we report a similar device fabricated using Sb₂ molecular implantation [A. M. Jakob, Adv. Mater. 2024, 36, 2405006], aiming to find Sb donors in proximity allowing entangling operations between the nuclei via geometric gates on the shared electron [Mądzik, M.T et al. Nature 601, 348–353 (2022)]. The device reported here has displayed signatures of two Sb donors asymmetrically coupled to a single electron.

Adiabatic ESR spectrum was performed where 8 possible resonance frequencies, separated by about 100 MHz, were observed due to the hyperfine coupling between the electron and the strongly coupled Sb donor (Strong). We then initialized the “Strong” in the -7/2 state and performed a coherent ESR scan where, again, 8 possible frequencies separated by around 100 kHz, were seen. These shifts result from the hyperfine coupling between the electron and the weakly coupled donor (Weak). We also measured the NMR spectrum of the “Strong” donor spin state using adiabatic ESR, and, while fixing the spin state of the “Strong” donor at -7/2, measured the NMR spectrum of the “Weak” and extracted the quadrupole splitting of 𝑓_{𝑞,𝑠𝑡𝑟𝑜𝑛𝑔}= 35 kHz, and 𝑓_{𝑞,𝑤𝑒𝑎𝑘}= 43 kHz respectively.