Coupling a Ge/Si nanowire quantum dot to a high-impedance resonator*

Hole spins in Ge/Si core/shell nanowires show a strong and electrically tunable spin-orbit (SO) interaction, allowing strong coupling between spins and photons, e.g. of a superconducting resonator. In addition, the hyperfine interaction is expected to be weak, reducing hyperfine decoherence. Recently, a highly tunable hole spin qubit with SO switch was demonstrated [1]. However, the readout so far has relied on transport through the nanowire, so the qubit was not operated in the few-hole regime.

Here, we present spectroscopy measurements on Ge/Si nanowire double quantum dot system using a high-impedance, magnetic-field resilient, high quality factor NbTiN resonator with a resonance frequency of ~3 GHz. DC current measurements and dispersive readout via the resonator sensed numerous hole transitions simultaneously. But once the DC transport was fully suppressed, we were still able to read dozens of transitions using solely spectroscopy. Following these transitions, we find first indications of depletion to the last hole. We are now aiming to coherently couple a photon from the resonator to the spin of a hole spin qubit in Ge/Si core/shell nanowires.