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Marion Bassi

Tunable resilience to charge noise of a hole spin

Published on 27 June 2024
​Thesis presented June 27, 2024

Spin quantum bits (qubits) established in group-IV semiconductor quantum dots structures (QD) embody a promising platform for large-scale quantum processors leveraging on small footprint and compatible fabrication processes with mainstream semiconductor industry. In particular, hole particles recently gained attention as spin qubit platform as they enable fast and all-electrical manipulation due to their intrinsically large spin-orbit coupling. The latter coupling however stands as a two-edged sword as it also exposes the hole spin to undesired interactions with the surrounding environment, which in turn degrade the qubit coherence time. Over the past years, many efforts have been conducted to mitigate electrical noise influence stemming from the environment thus revealing the existence of preferential points of enhanced coherence time, named ''sweetspots'', depending on magnetic field orientation.
In this manuscript, the emphasis is laid on the characterization of electrical noise contributions impacting a single hole spin qubit with respect to magnetic field orientation on a P-doped natural silicon-MOS architecture. The hole particle is spatially confined in a QD defined electrostatically within the device. The spin orientation is readout by radio-frequency reflectometry based on energy-selective readout method. We experimentally demonstrate that the reported ''sweetspots'' belong in fact to continuous ''sweetlines'' wrapped around the sphere of magnetic-field polar-angle components, in agreement with theoretical predictions. We also show that, in addition to extended coherence time, sweetline operation is compatible with efficient electric-dipole spin resonance with Rabi frequencies, ƒ​R, comfortably exceeding 10 MHz, and a qubit quality factor Q = 2ƒRT2R as high as 690, competing with reported values for electrons. Our study evidences ample gate-voltage control of the sweetlines position in magnetic field, an aspect particularly relevant in the purview of scalability. Finally, the experimental investigation of such optimal operation points is extended to a two qubit system as a proof of concept underscoring the importance of sweetlines tuning for spin qubit systems.

Hole spin, qubits, quantum dot, radio-frequency reflectometry, quantum computer, spin-orbit coupling, sweetspot, coherence time, sweetlines