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


Type

Thesis

Change log

Authors

Lundberg, Theodor William 

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.

Description

Date

2021-12-01

Advisors

Sirringhaus, Henning
Robinson, Jason WA
Gonzalez-Zalba, M Fernando

Keywords

dispersive readout, magnetospectroscopy, Pauli spin blockade, quantum computing, quantum dot, silicon, spin qubit

Qualification

Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge
Sponsorship
EPSRC (1948658)
Engineering and Physical Sciences Research Council (1948658)
European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 688539; EPSRC Cambridge NanoDTC, EP/L015978/1

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