Thesis presented June 09, 2021

Abstract:
Owing to ever increasing gate fidelities and to a potential transferability to industrial CMOS technology, silicon spin qubits have become a compelling option in the strive for quantum computation. However, hole spin qubits in silicon remain a barely explored hosting platform as compared to their electron counterpart. Hole spins carry some attractive properties: for instance, strong spin-orbit coupling enables fast coherent spin rotations using a radio-frequency electric field; also, we expect long coherence times due to the absence of contact hyperfine interaction. In this thesis, we conduct experiments on p-type silicon-nanowire devices to take advantage of the above mentioned properties.
In order to pave the way for large-scale quantum processors, the development of scalable qubit readout schemes involving a minimal device overhead is a compelling step. Here we report the implementation of gate-coupled RF reflectometry for the dispersive readout of a fully functional hole spin qubit device. We use a p-type double-gate transistor made using industry-standard silicon technology. The first gate confines a hole quantum dot encoding the spin qubit, the second one a helper dot enabling readout. The qubit state is measured through the phase response of a lumped-element resonator to spin-selective interdot tunneling. The demonstrated qubit readout scheme requires no coupling to a Fermi reservoir, thereby offering a compact and potentially scalable solution whose operation maybe extended above 1 K.
In a scalable architecture, each spin qubit will have to be finely tuned and its operating conditions accurately determined. In this prospect, spectroscopic tools compatible with a scalable device layout are of primary importance. Here we report a two-tone spectroscopy technique providing access to the spin-dependent energy-level spectrum of a hole double quantum dot defined in a split-gate silicon device. A first GHz-frequency tone drives electric-dipole spin resonance enabled by the valence-band spin-orbit coupling. A second lower-frequency tone (?500 MHz) allows for dispersive readout via rf-gate reflectometry. We compare the measured dispersive response to the linear response calculated in an extended Jaynes-Cummings model and we obtain characteristic parameters such as g-factors and tunnel/spin-orbit couplings for both even and odd occupation.

Keywords:
qubit, silicon, quantum computing, hole, spectroscopy, spin

On-line thesis.