Long-Range Exchange Coupling between Ge-Hole Spin Quantum Systems

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Quantum processors promise to tackle problems deemed unsolvable by classical computers, advancing fields such as finance, climate change, chemistry and cryptography, amongst others. Current leading platforms for quantum computation include superconducting qubits, ion traps and spins in quantum dots. While there have been many experiments on single-qubit operation in such platforms, two-qubit entangling operations still remain elusive, which are a crucial requirement for realising a useful quantum computer. As such, of interest are systems which can easily manipulate and couple qubits to achieve multi-qubit connectivity, while leveraging state-of-the-art qubit control and read-out techniques.This PhD project will therefore focus on the study of novel germanium-hole quantum-dot qubits, with the end goal of implementing and extending long-range coupling between spatially separated qubits. Hole spins in germanium are a particularly attractive platform due to fast manipulation speeds, low decoherence rates and ease of fabrication. The project will concern device design, modelling, measurement and characterisation, with considerations towards scaling this architecture. The majority of work will be carried out at the Hitachi Cambridge Laboratory (HCL), the industrial sponsor of this PhD. HCL are experts in gate-based qubit readout, with much work already performed on CMOS qubits. Devices will be fabricated by collaborators which are leaders in growing germanium structures. Due to the facilities and expertise in germanium qubits and long-range coupling techniques at the HCL, this project aims to advance qubit-to-qubit connectivity, paving the way towards scalable, universal quantum computation.