Coherent electric field control of spin systems for quantum technologies

Thesis

Spin systems offer a versatile platform for exploring fundamental phenomena and developing quantum technologies. Conventional manipulation of spin states with magnetic fields faces intrinsic limitations, including crosstalk and poor nanoscale confinement. Electric fields, by contrast, can be precisely localised, potentially opening new routes for scalable spin control and device integration.

This thesis investigates the electric-field control in spin systems exhibiting spin-electric coupling (SEC) and its relevance to quantum information and sensing. Chapter 2 presents a proof-of-concept electric-field quantum sensor based on an optically excited state in an organic molecular nanomagnet integrated into a capacitive device. Unlike conventional SEC that typically requires strong atomic spin-orbit coupling (SOC), the effect here arises from electric-field-induced redistribution of charge within the excited state. Notably, this mechanism yields a coupling strength comparable to that of SOC-driven systems, thus expanding the range of materials suitable for SEC studies.

In Chapter 3, we demonstrate the electric control of nuclear spins in magnetic defects within a semiconducting crystal. In this system, the electron-nuclear interaction, often suppressed in nuclear-spin qubits to preserve coherence, is harnessed to enhance nuclear SEC. The underlying mechanism relies on the electric field modulating the electron magnetic anisotropy, whose electric sensitivity is transferred to the nuclei via the hyperfine coupling. Using this approach, we were able to drive nuclear spin transitions using resonant electric fields. Building on these results, Chapter 4 investigates electrically driven electron transitions, proposing a resonator architecture for their investigation and analysing possible mechanisms that mediate them.

Finally, Chapter 5 explores the SEC in polyoxometalate molecular complexes and introduces strategies to generate and electrically control their clock transitions, that is, spin transitions whose energy is, to first order, independent of the magnetic field. We further propose a theoretical scheme for generating entanglement between two clock spins, marking a step toward the development of scalable multi-qubit platforms.

Taken together, the studies presented in this thesis advance spin-based quantum technologies by establishing a foundation for fully electrical control of spin systems.

Authors: Fontana, N

• DOI: 10.5287/ora-pmokodvkx
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: electron spin resonance; quantum information science; spin systems; spin-electric coupling; molecular magnetism
• Subjects: Experimental Condensed Matter Physics; Experimental Physical Chemistry