Gate Tunable Hole Charge Qubit Formed in a Ge/Si Nanowire Double Quantum Dot Coupled to Microwave Photons

A controllable and coherent light-matter interface is an essential element for a scalable quantum information processor. Strong coupling to an on-chip cavity has been accomplished in various electron quantum dot systems, but rarely explored in the hole systems. Here we demonstrate a hybrid architecture comprising a microwave transmission line resonator controllably coupled to a hole charge qubit formed in a Ge/Si core/shell nanowire (NW), which is a natural one-dimensional hole gas with a strong spin–orbit interaction (SOI) and lack of nuclear spin scattering, potentially enabling fast spin manipulation by electric manners and long coherence times. The charge qubit is established in a double quantum dot defined by local electrical gates. Qubit transition energy can be independently tuned by the electrochemical potential difference and the tunnel coupling between the adjacent dots, opening transverse (σx) and longitudinal (σz) degrees of freedom for qubit operation and interaction. As the qubit energy is swept across the photon level, the coupling with resonator is thus switched on and off, as detected by resonator transmission spectroscopy. The observed resonance dynamics is replicated by a complete quantum numerical simulation considering an efficient charge dipole-photon coupling with a strength up to 2π × 55 MHz, yielding an estimation of the spin-resonator coupling rate through SOI to be about 10 MHz. The results inspire the future researches on the coherent hole-photon interaction in Ge/Si nanowires.