Anisotropic spin-valley coupling in Si/SiGe quantum dots

Silicon-based quantum computers leverage established fabrication techniques to create stable gate-defined quantum dots and achieve long qubit coherence times. While spin-orbit coupling is weak in bulk silicon, it is enhanced at the silicon interface with SiO₂ in SiMOS or with SiGe in Si/SiGe quantum wells. This can be used for spin qubit control through, e.g., intervalley spin-orbit coupling [1,2]. However, this same control mechanism may also lead to rapid qubit relaxation when the Zeeman energy is similar to the valley splitting [3,4]. In this work, we investigate both intra- and intervalley spin-orbit coupling in a Si/SiGe quantum dot device using an angle-resolved magnetospectroscopy technique. We monitor the singlet-triplet qubit rotation frequency while varying the magnetic field magnitude and direction and observe magnetic field orientation-dependent spin-valley coupling. We use these data to parameterize a model that captures the magnetic field dependence of g-factor differences and spin-valley coupling. Finally, we compare our Si/SiGe results to similar measurements in a SiMOS device.

[1] Jock, R. M. et al. Nat. Comm. 13, 641 (2022)

[2] Cai, X. et al. Nat. Phys. 19, 386 (2023)

[3] Yang, C. H. et al. Nat. Comm. 4, 2069 (2013)

[4] Zhang, X. et al. PRL 124, 257701 (2020)



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