PhD defence by Amedeo Carbone

Abstract

Over the past decade, extremely thin materials—only a single atom thick—have transformed research in physics and materials science. These “two-dimensional” (2D) materials include graphene and hexagonal boron nitride (hBN). Because they are so thin and have novel interesting electrical and optical properties, they are promising building blocks for the next generation of electronic and quantum technologies.

A particularly exciting discovery is that defects in the crystal structure of these materials can act as sources of quantum light, that means they can emit only one photon at a time. Such quantum light sources are important for future technologies like secure communication, sensitive detectors, and quantum computers. But to use them reliably, scientists need ways to create these defects on purpose, measure them accurately, and eventually control them using electrical signals, much like today’s semiconductor devices.

This PhD work focuses on one specific defect in hBN: the negatively charged boron vacancy, in which a boron atom is missing from the crystal. The research tackles two main challenges. First, it investigates how to deterministically create these defects using a focused beam of helium ions. By adjusting the number of ions that hit the material, the study measures how efficiently the defects are formed and how many of them become useful light-emitting centers. This is done by combining optical experiments with a microscopic charge model that helps explain how many defects are in the desired charge state.

The second part of the thesis builds the first steps toward electrical control of these quantum emitters. By placing hBN between two thin layers of graphite, the work demonstrates that an applied voltage can influence how electrons and holes move through the defects and even suppress their light emission under certain conditions. This provides an initial route toward devices where quantum light sources could be switched or tuned electrically.

Overall, the thesis contributes both practical techniques and theoretical insight into how quantum emitters can be engineered in layered materials. These results pave the way for scalable, electrically addressable quantum light sources that could one day form the basis of advanced photonic circuits and quantum technologies.

Supervisors

• Principal supervisor: Associate Professor Nicolas Stenger, DTU Electro, Denmark
• Co-supervisor: Associate Professor Alexander Huck, DTU Physics, Denmark
• Co-supervisor: Professor Alexander Holleitner, TUM, Germany
• Co-supervisor: Dr. Christoph Kastl, TUM, Germany
• Co-supervisor: Professor Martijn Wubs, DTU Electro, Denmark

Evaluation Board

• Associate Professor Timothy Boots, DTU Physics, Denmark
• Professor Vladimir Dyakonov, Julius Maximilian Universität Würzburg, Germany
• Professor Tobias Vogl, TUM, Germany

Master of the Ceremony

• Co-supervisor, Dr. Christoph Kastl, TUM, Germany