Molecular Strong Coupling and Entanglement Formation in Extreme Nanophotonic Environments

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Nanoscale photonic environments, supporting light-matter interactions with molecules or cold atoms, are at the heart of nano-optics. This work focuses on developing quantum mechanical models to better understand such systems and the design of novel photonic environments for use in quantum information technologies. The following are brief summaries of my ongoing work. Quantum networks exploit both local and global entanglement over separated network nodes to provide unbreakable encryption and scalable computation. However, most high-fidelity local nodes are only weakly coupled to the electromagnetic field, limiting the inter-node entanglement rate. Further to this, almost all strongly coupled photonic devices are made of silicon and operate at telecommunication wavelengths, making them unsuitable for entanglement with cold atoms. In this work, we design nanophotonic crystal resonators that overcome these challenges, commanding unprecedented optical confinement and strong field enhancements while operating at 780 nm for entanglement with rubidium. Our designs exist deep into the strong coupling regime, where we demonstrate local multipartite entanglement that is robust to displacement of the trapped atoms. High fidelity entanglement and a scalable photonic architecture make our systems ideal for constructing large quantum networks, where both local and remote entanglement can be realized.Nonreciprocal devices, possessing direction dependent wave propagation, are a key component in quantum information technologies as they act to protect qubits from reflections and noise. It has recently been shown that quantum nonreciprocity can be generated in passive devices, without an external bias, but instead induced through a combination of system nonlinearity and spatial symmetry breaking. In this work we adapt our cavity design to create a realistic photonic crystal waveguide, coupled to two detuned cold atoms, that exhibits nonreciprocity through excitation of a slowly decaying dark state. By expanding the model to larger numbers of atoms, we aim to overcome the theoretical two-atom efficiency and create a system with superior nonreciprocity.Plasmonic structures facilitate rapid energy exchange between light and molecules, overcoming large heating losses in the metal through confinement of light well below the diffraction limit. Semi-classical and fully quantum formalisms are employed to describe these phenomena. However, most assume the interaction is between a two-level system and a single plasmonic resonance, neglecting a large collection of higher order modes and the complex molecular structure. In this work, we treat the plasmonic cavities as open systems, supporting a set of quasi-normal modes (QNM's) with complex eigenfrequencies. We reveal the impact of high-order modes on the single molecule dynamics and semi-persistent entanglement generation between two molecules. Numerical simulations are performed within the nanoparticle on mirror cavity, and similar systems with morphological changes to the facet shape, making them ideal for room temperature entanglement generation and quantum technologies.