A singlet triplet hole spin qubit in planar Ge

Abstract

Spin qubits are considered to be among the most promising candidates for building a quantum processor. GroupIV hole spin qubits have moved into the focus of interest due to the ease of operation and compatibility with Si technology. In addition, Ge offers the option for monolithic superconductor-semiconductor integration. Here we demonstrate a hole spin qubit operating at fields below 10 mT, the critical field of Al, by exploiting the large out-of-plane hole g-factors in planar Ge and by encoding the qubit into the singlet-triplet states of a double quantum dot. We observe electrically controlled g-factor-difference-driven and exchange-driven rotations with tunable frequencies exceeding 100 MHz and dephasing times of 1 $\mu$s which we extend beyond 150 $\mu$s with echo techniques. These results demonstrate that Ge hole singlet-triplet qubits are competing with state-of-the art GaAs and Si singlet-triplet qubits. In addition, their rotation frequencies and coherence are on par with Ge single spin qubits, but they can be operated at much lower fields underlining their potential for on chip integration with superconducting technologies.