Nonlinear quantum optics using Rydberg excitons

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The 20th century has witnessed the birth of quantum mechanics, a microscopic theory which defied every bit of intuition regarding the world around us. This discovery, led to pioneering insights about the nature of light, matter, and their interaction at the absolute smallest scales. Subsequently, this gave birth to a new era of technological civilisation with the invention of semiconductors, and the laser. Now, we are at the dawn of a second quantum revolution, where it is thought to be responsible for most of the key technological advancements of the 21st century. From virtually unhackable communications, to synthetic materials with exotic properties, quantum technologies constitute the common denominator for these advancements.While the scientific community is pushing towards the implementation of quantum hardware on a variety of platforms, a prominent candidate that has recently emerged as a solid-state solution is the cuprous oxide. Owning to its large binding energy and high optical purity, observation of Rydberg-state excitations was possible in samples of naturally occurring cuprous oxide. Rydberg excitations possess exaggerated properties like large radii and transition dipole moments, strong polarisability and long radiative lifetimes, controlled by state selection and application of external fields. These properties lead to strong van der Waals forces between different excitations within the crystal, that dominate over several microns. This grants capability to engineer interactions between spatially separated spins and photons, while preserving state read-out capability via optical means.This work is multi-faceted, and firstly we will focus on the growth of synthetic cuprous oxide micro-crystals that are of high optical purity, at the available thin-film deposition and annealing facilities at the University of Oxford. While working on synthetic crystal growth, an effort will run in parallel to design and assemble an all-optical experiment operating at cryogenic temperatures which will be the main characterisation station. Characterisation of the samples will be made possible by employing reflection-based photoluminescence spectroscopy, both at zero and finite magnetic fields, and real-space microscopy techniques like scanning confocal microscopy. Spectroscopy will allow us to probe the quality of the synthetic samples, while scanning confocal microscopy will allow to construct photoluminescence maps and grant the option to deterministically steer the beam to optically active areas of interest. Moreover, a combination of continuous-wave and pulsed lasers will aid in tailoring and characterising the spin-state of the Rydberg excitations. At a later stage, this project will focus on the deterministic positioning of individual micro-crystals on a platform that is compatible with current chip manufacturing industry-standards and investigate the possibility of integrating this platform with electronic and photonic components, as a pathway towards on-chip programmable quantum simulation of spin models.This project falls under the "Quantum optics and information" research area.