Distributing quantum information with holes in germanium

Abstract

In this thesis, research is presented that explores the characteristics and possibilities of hole spin qubits defined in quantum dots in a germanium/silicon germanium heterostructure. The results of the most important experiments are concerned with distributing quantum information: either by entangling three qubits as the basis for the phase flip code or by shuttling quantum information encoded in a spin qubit. Chapter 2 gives a brief description of the experimental and theoretical background needed to understand the experiments presented in this thesis. The focus lies on the theory that is specific for hole spin qubits in germanium/silicon germanium, in contrast to electron spin qubits in other semiconductor platforms. In chapter 3, the properties of a two-by-two quantum dot device that could facilitate hole spin qubits are discussed, including shell filling and control over the tunnel coupling between the quantum dots. Chapter 4 provides a detailed discussion of the features of a two-by-two qubit system, showing high-fidelity single qubit gates and the implementation of two-, three-, and four-qubit gates. This two-by-two qubit system is used to implement the Phase flip code, of which the results are shown in chapter 5. To facilitate this, the SWAP, CS−1 and the Toffoli-like gate are demonstrated. Chapter 6 explores the possibilities of diabatically shuttling a hole spin qubit through multiple quantum dots. The effects of spin-orbit interaction and the shuttling performances are described. Finally, Chapter 7 discusses the results presented in this thesis and provides an outlook.