Dynamical decoupling spectroscopy of nuclear quadrupole transitions in an exchange-only qubit: Theory

The decoherence of Si/SiGe spin qubits due to magnetic nuclei can be greatly suppressed using dynamical decoupling [1,2]. However, highly periodic decoupling sequences can resonantly couple to magnetic transitions of high-spin atoms. In Si/SiGe exchange-only triple-dot qubits, the most important source of these transitions is the internal magnetic structure of the spin-9/2 ⁷³Ge nuclei. In this talk, first-principles calculations of SiGe atomic and electronic structure will be used to predict the spectroscopic features created by these quadrupolar nuclei. We find that the strain induced by SiGe alloy disorder translates to a specific distribution of electric field gradients (EFG) seen by the ⁷³Ge atoms. These EFGs in turn set the magnetic quadrupole energy scales at which resonant coupling between qubit and nuclei occur.

[1] Kerckhoff, et al. PRX Quantum 2, 010347 (2021)

[2] Sun, et al. PRX Quantum 5, 020356 (2024)