Magnetic field study of spin-orbit and nuclear spin dynamics on singlet-triplet qubit coherence in Si/SiGe quantum dots

Multi-qubit platforms based on Si/SiGe heterostructures are attractive because of their long coherence times and well-established fabrication processing, but are nonetheless limited by intrinsic material qualities that drive dephasing. One contribution is the spin-orbit interaction that arises from interfacial disorder and inversion asymmetry in the crystal lattice and can induce qubit susceptibility to charge noise through electrostatic variations in the electron g-factor. Another intrinsic contribution to dephasing is due to the contact hyperfine interaction with ²⁹Si within the Si quantum well (QW) and both ²⁹Si and ⁷³Ge in the SiGe barriers. In this work, we explore decay dynamics of a spin-orbit driven singlet-triplet qubit hosted in a gate-defined 3QD device fabricated by Intel Corporation consisting of an isotopically purified 5 nm Si QW (800 ppm ²⁹Si) within a Si/SiGe heterostructure. We map out the magnetic field angle- and magnitude-resolved dependence of T₂* and T₂^Hahn and observe variations in coherence. We compare the results with the field dependence of the spin-orbit and hyperfine interactions to assign their relative contributions to noise, and make interpretations of the underlying physical mechanisms by modeling decay dynamics. The results aim to shed light on coherence-limiting mechanisms in spin qubits and offer a pathway to minimizing their detrimental effects.

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