Noise-Robust Spin-Orbit Qubit in Germanium Holes via p-Orbital Encoding

Abstract

Germanium hole spin qubits are a leading platform for semiconductor quantum computation due to their strong spin-orbit coupling, all-electrical operability, and absence of valley degeneracy. A central obstacle is charge noise, which couples to the qubit through the same spin-orbit interaction that enables fast electrical control. In this work, we propose a new operational mode of a three-hole quantum dot in a planar Ge/SiGe heterostructure, modeled within a four-band Luttinger-Kohn--Bir-Pikus framework: a spin-$p$-orbital (SpO) qubit encoded in the $p$-shell of the topmost hole. We characterize charge noise sweet spots in the parameter space of electrostatic confinement and magnetic field, and estimate that relaxation rates of the SpO qubit are comparable to those of spin qubits hosted in single holes. We then design and optimize an all-electrical Landau-Zener state-transfer protocol that induces logical qubit state transitions without microwave driving, and we show that the quadrupole-quadrupole Coulomb interaction between neighboring dots enables fast two-qubit entangling gates operated by adiabatic shuttling.