PhD defence by Rohan Radhakrishnan

Abstract

The development of quantum technologies promises a revolution in how we communicate, compute, and sense the world around us. At the heart of these emerging technologies lies the ability to control individual particles, such as electrons or photons, which are particles of light. My PhD research focuses on designing and studying quantum dots, tiny semiconductor nanostructures that can trap single electrons and emit single photons.

A quantum dot acts like an artificial atom: it has discrete energy levels, and when it is excited by light, it emits one photon at a time. But, unlike a natural atom, it can be engineered to change its properties. Researchers have recently developed multiple innovative fabrication methods for building the best quantum dots; however, most of them do not offer a high degree of designability and are limited to the fabrication of single quantum dots, lacking the necessary scalability for quantum photonic technologies.

Fabricating quantum dots inside a nanowire stands out thanks to its intrinsic ability to build them on top of each other along the nanowire axis. My research explores multiple aspects of this platform. Firstly, I show that AlGaAs nanowires are a universal platform that can host quantum dots made with different materials (GaAs, InGaAs, and InAs) that usually require different hosting platforms. Next, I explore a type of quantum dot not defined by its material composition but by its crystal structure. Known as crystal-phase quantum dots, I study a few of their properties in AlGaAs nanowires, where they are still unexplored. Moreover, I show how they can be deterministically fabricated in GaAs nanowires along with good optical properties. Finally, I present the concept of the location qubit, a new qubit definition specifically developed to leverage multi-quantum dot systems in building a photonic quantum processor — an essential building block of the emerging quantum internet.

Supervisors

• Main Supervisor: Associate Professor Nika Akopian, DTU Electro
• Co-supervisor: Associate Professor Christos Markos, DTU Electro

Assessment committee

• Associate Professor Luca Vannucci DTU Electro (chair)
• Research Director Julien Claudon, SP2M then PHELIQS (CEA Grenoble, France)
• Head of Department Sabbir Ahmed Khan, DFM-Danish National Metrology Institute, Denmark

Master of the Ceremony

• Senior Researcher Philip Trøst Kristensen, DTU Electro, Denmark