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

The leading cause of memory decoherence in SiGe spin qubits is magnetic interations with spinful nuclei [1]. In recent years, the role of interactions with spin-9/2 ⁷³Ge nuclei has been emphasized [2]. HRL Laboratories has recently demonstrated a dynamical decoupling sequence for exchange-only qubits, called NZ1, which can be used as an incisive probe of magnetic error contributions [3]. In this talk, we explore the dependence of NZ1 fidelity on both  and the operating magnetic field . We find multiple regions of increased noise that arise from resonant coupling between the NZ1 sequence and magnetic transitions with ⁷³Ge nuclei. This two-dimensional mapping of the NZ1 sequence reveals rich noise structures: we identify these with variations in electric field gradients due to SiGe alloy disorder in our device.

 

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

[2] Cvitkovich, et al. Phys. Rev. App. 22, 064089 (2024)

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