Extreme Harmonic Generation in an InAs Spin-Orbit Qubit*

Strong spin-orbit materials have shown great promise in the field of quantum computation. Unlike conventional semiconductor materials, fast all-electrical control is achieved through electric dipole spin resonance (EDSR). In this work we explore EDSR in an InAs nanowire spin-orbit qubit. We observe signs of harmonic generation where spin flips occur at the resonance condition $n h f = g \mu_{\rm B} B$, where $f$ is the applied frequency, $B$ is the magnetic field, $g$ is the $g$-factor and $n$ is an integer. Near the interdot charge transition we observe harmonics up to $n$ = 8, indicating extreme harmonic generation. At far detuning we only observe the $n=1$ resonance. Further, we find odd/even structure in the harmonic response: odd harmonics result in an increase in the leakage current while even harmonics result in its suppression. Finally we observe oscillations in the resonant current as a function of detuning. The striking detuning dependence suggests that the harmonics may be caused by Landau-Zener transitions occurring due to the anti-crossing between the differing charge states. Numerical simulations of the system are qualitatively consistent with this picture.