Dispersive Readout and Spin-State Spectroscopy of Industrially-Fabricated Silicon Quantum Dots

Abstract

Encouraged by the promise of large-scale quantum computing, this thesis focuses on reliable and scalable readout of spin qubits in gate-defined silicon complementary metal-oxide-semiconductor quantum dots. In particular, this thesis studies the spin states and Pauli spin blockade (PSB) physics of silicon quantum dots using scalable gate-based dispersive sensing and magnetic-field-assisted energy spectroscopy. In the first part of the thesis, I present an expanded description of the PSB-physics of a tunnel-coupled silicon double quantum dot defined in the corners of a split-gate transistor. Using gate-based magnetospectroscopy and by developing a quantum capacitance model for reconstruction of quantum dot energy spectra, I report successive steps of PSB and PSB-lifting involving spin states with total spin angular momentum up to S = 3. More particularly, I discover the formation of a hybridized spin quintet state and the presence of triplet-quintet and quintet-septet PSB. This enables studies of the quintet relaxation dynamics from which I find a characteristic relaxation time of T1 ~ 4 μs. Subsequently, I present an experimental observation of a new, highly prevalent PSB-lifting mechanism in a silicon double quantum dot due to incoherent tunneling between different spin manifolds. Through dispersively-detected magnetospectroscopy of the double quantum dot in 16 charge configurations, I find the mechanism to be energy-level selective and non- reciprocal for neighbouring charge configurations. Additionally, I report a large coupling of different electron spin manifolds of 7.90 μeV, the largest reported to date, indicating an enhanced spin-orbit coupling which may enable all-electrical qubit control. Finally, I introduce Pulse Assembler, a software tool developed to aid execution of spin qubit control experiments. Designed to combine the strengths of the Qiskit, Pulse lib and QCoDeS software packages, Pulse Assembler introduces a JSON-file-based representation of qubit control pulses that allows parametrisation of any pulse parameter. As a result, pulse parameter sweeps can be implemented in just a few lines of code.