Dispersive charge sensing in Ge/Si core/shell nanowire quantum dots*

Germanium/silicon core/shell nanowires are a powerful platform to study and optimize the properties of the hole spin qubits. The p-type hole wavefunction does not suffer from the contact hyperfine interaction, promising long coherence times. Another advantageous property is the strong and electrically tunable direct Rashia spin-orbit interaction (dr-SOI) [1], which allows switching between ultrafast qubit manipulation with Rabi frequency above 400 MHz [2], and an idling regime with weak SOI and long coherence time. Additionally, strong SOI enables the electrical tunability of the Lande g-factor useful e.g. for the implementation of a phase-gate but also opens a decoherence channel by coupling the spin to the charge noise.

Here, we optimize the device fabrication and in particular the oxides by adding annealing steps that can passivate interface traps, with the goal to reduce charge noise and increase the qubit coherence. We also show the progress towards establishing the gate-based dispersive charge sensing aiming for the few-hole regime and fast single-shot spin readout.

[1] Froning et al., Phys. Rev. Research 3, 013081 (2021)

[2] Froning et al., Nat. Nanotechnol. 16, 308 (2021)