Electrical behaviour of quantum systems at high frequencies - Bridging the gap between transistor and qubit

Devices harnessing quantum phenomena have made tremendous progress in the last decade, irreversibly changing the scientific and technological landscape. Quantum technologies have unlocked unprecedented performance and capabilities, while quantum computing has demonstrated computational advantage, ushering in a new paradigm of conceiving information processing, and inching closer to Feynman's dream of performing tasks classically out of reach within the lifetime of the Universe. As technology progresses towards fault-tolerant quantum information processing, scaling of quantum systems becomes increasingly important to unleash the full potential of the quantum dynamics. This requirement for large-scale integration, however---and the consequent necessity for optimization in such a resource-constrained problem---requires a deep understanding of the physics underlying quantum devices and their operation. Moreover, the interaction of quantum systems with larger classical circuits they are embedded within is a treasure trove of emergent phenomena with the potential of becoming quantum technologies in their own right or key enabling technologies for quantum computation. Scalable solid-state quantum technologies require reliable modelling to confidently design systems containing the large number of qubits necessary to perform tasks of societal impact, as well as aiding the integration with analogue and digital electronics necessary for their practical use. This thesis represents a bridge between the physical description of quantum phenomena and the electrical behaviour that originates when quantum systems are embedded in larger classical networks, with the aim of abstracting the complexity of quantum mechanics and thus enabling the design and engineering of complex devices. This thesis constructs from first principles the theory of quantum-classical modelling and co-simulation and details its application in varied quantum-dot-based devices, such as charge and spin qubits and open quantum systems. Theoretical models are accompanied by novel experimental results, demonstrating the capabilities of the underlying theoretical frameworks, investigating fundamental physical phenomena, and showcasing novel applications of quantum devices. This thesis explores several aspects of quantum dynamics in the solid state and its resulting electrical behaviour. It presents a unified linear response theory capable of ranging from the semiclassical to the coherent regime, providing the small-signal electrical response of an arbitrary quantum system in the form of a repeated network of linear circuit elements. This is leveraged to describe the electrical response of a double quantum dot charge qubit, exploring novel regimes such as the resonant excitation of a coherent qubit---hitherto sole territory of circuit quantum electrodynamics---and observing the disappearance of coherent features in the limit of fast decoherence. Moreover, this thesis presents a beyond-adiabatic model for the single electron box and explores the novel regimes predicted by the theory, investigating the nature of coherent quantum interference in a strongly dissipative open quantum system. A single electron box and a double quantum dot are also employed to experimentally demonstrate the use of nonlinear quantum systems as a frequency multiplier based on single-electron transitions. The spin and charge dynamics in a doubly occupied double quantum dot in the presence of spin-orbit coupling are also explored, with particular emphasis on Pauli spin blockade and its lifting. This is recast in an analogy with the well-known technique of polarimetry, offering an intuitive explanation of the complex spin dynamics---substantiated by experimental observation---with implications on the achievable fidelity of rapid spin readout. Furthermore, this work showcases how the modelling framework constructed throughout this thesis is compatible with industry-standard (classical) electrical circuit simulators, enabling quantum technologies to leverage the multiple decades of development in electronic computer-aided design and automation tools in the semiconductor industry. Overall, this work demonstrates how accurate modelling of the electrical behaviour of quantum systems is paramount for the understanding of nanoscale physics, enabling both novel scientific exploration of the boundaries between quantum and classical regimes, and allowing the technological exploitation of quantum phenomena. For the purpose of quantum information processing, this modelling effort provides the key advantage of abstracting the complex quantum-mechanical device physics behind their corresponding electrical characteristics, allowing quantum technologies to participate in the design paradigms that have enabled the unprecedented scaling of classical electronics, laying a concrete path towards very large-scale quantum integration.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Peri, Lorenzo

Advisors dc:contributor.advisor

• Ford, Christopher JB
• Gonzalez-Zalba, M Fernando

• Qubits
• Quantum dots
• Quantum modelling
• Spin

Licence

• https://www.repository.cam.ac.uk/bitstreams/90f58384-30a8-4995-acb1-0f40577f1fba/download
• https://creativecommons.org/licenses/by/4.0/

Language dc:language

eng

Author Identifier

0000-0002-3603-1648

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/392660