Gate tunable spin splitting of germanium quantum well Josephson junction.

Proximitized Ge heterostructures are a promising host platform for Andreev qubits and topological qubits because of their strong spin-orbit coupling, high mobility, and naturally low abundance of nuclear spins [1]. An important distinction between Ge and traditional Andreev qubit materials like InAs is the form of their Rashba spin-orbit coupling, which is linear in momentum for InAs but cubic for Ge. Here, we compare the effects of linear vs cubic spin-orbit coupling on the spin splitting of the Andreev bound spectrum. Our numerical calculations indicate a distinct spin-splitting behavior as a function of chemical potential and junction width. Despite suggestions that Ge could be more resilient to charge noise, we show that the effect of charge traps on spin splitting is similar in both cases. These results highlight some of the benefits and challenges for using Ge as a platform for Andreev spin qubits.

References:

[1]Scappucci, G. et al. Nat. Rev. Mater. 6, 926 (2021).