Optical and RF Engineering of Bismuth in Silicon Devices

Group‑V donor spins in silicon are leading solid‑state platforms for long‑coherence quantum technologies. Bismuth in silicon (Si:Bi) is unique, the electron spin S = 1/2 couples to a large nuclear spin I = 9/2 via a strong isotropic hyperfine interaction A ≈ 1.475 GHz. This produces a zero‑field manifold split by ≈ 5A ≈ 7.38 GHz with field‑dependent structures and “clock‑like” (ZEFOZ) operating points that suppress first‑order magnetic dephasing. We focus on understanding and modeling the Si:Bi level structure as a function of magnetic field; performing and interpreting Hahn spin‑echo measurements in the 2–7 GHz bands to extract T2; using two‑pulse techniques in the THz to access donor valley‑orbit transitions.

We drive an ESR transition with frequency f(B0) chosen from the Si:Bi manifold. For a target frequency (e.g., 2 GHz or 7 GHz), the operating field B0 is near f/(ge μB/h), shifted by hyperfine mixing. Transitions near ZEFOZ regions can offer improved dephasing immunity (small ∂f/∂B), though weaker.

Transitions for the donor 1s manifold, such as 1s(A1) → 1s(T2) lie in the several‑THz band, accessed via long wavelengths at the HFML-FELIX Institute. Two phase‑coherent pulses separated by delay T drive the A1→excited‑state coherence, combined with the GHz source allow us to perform RF engineering of this optical system. We confirm our finding against models validated up to 30T.