Abstract
The spin-orbit interaction lies at the heart of quantum computation with spin qubits, research on topologically non-trivial states, and various applications in spintronics. Hole spins in Ge/Si core/shell nanowires experience a spin-orbit interaction that has been predicted to be both strong and electrically tunable, making them a particularly promising platform for research in these fields. We experimentally determine the strength of spin-orbit interaction of hole spins confined to a double quantum dot in a Ge/Si nanowire by measuring spin-mixing transitions inside a regime of spin-blockaded transport. We find a remarkably short spin-orbit length of $\sim$65 nm, comparable to the quantum dot length and the interdot distance. We additionally observe a large orbital effect of the applied magnetic field on the hole states, resulting in a large magnetic field dependence of the spin-mixing transition energies. Strikingly, together with these orbital effects, the strong spin-orbit interaction causes a significant enhancement of the $g$-factor with magnetic field.The large spin-orbit interaction strength demonstrated is consistent with the predicted direct Rashba spin-orbit interaction in this material system and is expected to enable ultrafast Rabi oscillations of spin qubits and efficient qubit-qubit interactions, as well as provide a platform suitable for studying Majorana zero modes.
Highlights
The spins of single electrons or holes can be coupled to orbital degrees of freedom through the spin-orbit interaction
In a solid-state environment, this interaction arises from the motion of electrons or holes in electric fields associated with the host lattice atoms, structural or bulk inversion fields, or externally applied electric fields, and its strength can range from a typically small perturbation in the conduction band to a significant effect in the valence band [1]
Summarizing, we have characterized the strength of spinorbit interaction for hole spins confined in a double quantum dot in a Ge/Si nanowire, using spectroscopy measurements in Pauli spin blockade
Summary
The spins of single electrons or holes can be coupled to orbital degrees of freedom through the spin-orbit interaction. Of spin-orbit interaction strength promises exquisite control over qubit coherence and manipulation speeds, providing a gate-controlled ON/OFF switch of the coupling to electrical environmental degrees of freedom, which could be used to, on the one hand, maximize the coupling to microwave drive fields and, on the other hand, minimize the coupling to charge noise Such controllable coupling would make it possible to combine ultrafast qubit operations with long coherence times. Due to the tunable nature of the spin-orbit interaction, the magnitude of the g factor of hole spins in Ge/Si nanowires can be modulated over a large range using applied electric fields [26,27] This feature enables local control over the Zeeman energy and allows to tune the energy of a qubit relative to a spin resonance driving field, or to a microwave cavity mode, making it possible to selectively address individual qubits in a multiqubit device. It causes a renormalization of the g factor, which we find here to lead to a Zeeman energy that is a nonlinear function of the applied magnetic field
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