Vukusic, Lada

Charge sensing and spin relaxation times of holes in Ge hut wires - IST Austria 2018

Thesis

Abstract Acknowledgments About the Author List of Publications List of Tables List of Figures List of Abbreviations 1 Introduction 2 Self-assembled SiGe nanostructures 3 Basics of transport in quantum dots 4 Fabrication and measurement techniques 5 Charge sensing in Ge hut wires 6 Hole tunnelling times in Ge hut wires 7 Single-shot readout of hole spins in Ge 8 Conclusion and outlook Bibliography A Fabrication details B Electrical circuit components C Rise time calculation D Software

A qubit, a unit of quantum information, is essentially any quantum mechanical two-level system which can be coherently controlled. Still, to be used for computation, it has to fulfill criteria. Qubits, regardless of the system in which they are realized, suffer from decoherence. This leads to loss of the information stored in the qubit. The upper bound of the time scale on which decoherence happens is set by the spin relaxation time. In this thesis I studied a two-level system consisting of a Zeeman-split hole spin confined in a quantum dot formed in a Ge hut wire. Such Ge hut wires have emerged as a promising material system for the realization of spin qubits, due to the combination of two significant properties: long spin coherence time as expected for group IV semiconductors due to the low hyperfine interaction and a strong valence band spin-orbit coupling. Here, I present how to fabricate quantum dot devices suitable for electrical transport measurements. Coupled quantum dot devices allowed the realization of a charge sensor, which is electrostatically and tunnel coupled to a quantum dot. By integrating the charge sensor into a radio-frequency reflectometry setup, I performed for the first time single-shot readout measurements of hole spins and extracted the hole spin relaxation times in Ge hut wires.

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