Large and tunable g-factor differences in planar-Ge hole singlet-triplet qubits*

Hole spins in Ge heterostructures bring together several exceptional properties, which makes them
one of the most promising candidates for the realization of a spin based quantum processor. Firstly,
holes couple weakly with nuclear spins resulting in large coherence times. Secondly, the large spin-
orbit coupling allows fast and fully electrical spin state manipulation. Finally, the small effective mass
and the low disorder in this material allow spin qubit nanodevices with complex designs. Very recent
experiments have demonstrated high-quality qubits operating in depletion mode [1], two qubit
gates [2] and 4-qubit devices [3].
Here we show the two-axis operation of a singlet-triplet qubit formed in planar Ge DQDs. X-axis
rotation frequencies of more than 100 MHz already at static magnetic fields of a few mT are
achieved due to the large g-factor difference (Δg) between the dots. We show that this large g-factor
difference is an intrinsic feature of planar Ge singlet-triplet qubits and investigate the Δg tunability
with the DQD hole occupation number and the middle barrier gate voltage.
[1] D Jirovec, et al. arXiv:2011.13755 (2020)
[2] N W Hendrickx, et al. Nature 577,487-491 (2020)
[3] N W Hendrickx, et al. arXiv:2009.04268 (2020)