Molecular Strong Coupling and Entanglement Formation in Extreme Nanophotonic Environments

纳米尺度的光子环境支持光与分子或冷原子的相互作用，是纳米光学的核心。这项工作的重点是开发量子力学模型，以更好地理解此类系统，并设计用于量子信息技术的新型光子环境。以下是我正在进行的工作的简要总结。量子网络利用独立网络节点上的局部和全局纠缠来提供不可破解的加密和可扩展的计算。然而，大多数高保真的局部节点只与电磁场弱耦合，限制了节点间的纠缠速率。此外，几乎所有的强耦合光子器件都是由硅制成的，工作在电信波长，这使得它们不适合与冷原子纠缠。在这项工作中，我们设计了纳米光子晶体谐振器，克服了这些挑战，在780 nm工作时获得了前所未有的光学限制和强场增强，用于与Rb的纠缠。我们的设计深入到强耦合区域，在那里我们展示了局域多体纠缠，这种纠缠对囚禁原子的位移是健壮的。高保真纠缠和可扩展的光子体系结构使我们的系统成为构建大型量子网络的理想选择，在那里可以实现本地和远程纠缠。非互易器件具有方向相关的波传播，是量子信息技术的关键组件，因为它们可以保护量子比特免受反射和噪声的影响。最近的研究表明，量子非互易性可以在无外加偏置的无源器件中产生，而是通过系统非线性和空间对称性破缺的组合来诱导的。在这项工作中，我们调整了我们的腔设计，以创建一个现实的光子晶体波导，耦合到两个失谐的冷原子，通过激发缓慢衰减的暗态表现出非互易性。通过将模型扩展到更多的原子，我们的目标是克服理论上的双原子效率，并创建一个具有优越的非互易性的系统。等离子体结构促进了光和分子之间的快速能量交换，通过将光限制在远低于衍射极限的范围内，克服了金属中的巨大热损失。半经典和全量子形式被用来描述这些现象。然而，大多数假设是两个能级系统和单个等离子体共振之间的相互作用，忽略了大量的高阶模式和复杂的分子结构。在这项工作中，我们将等离子体腔视为开放系统，支持一组具有复本征频率的准简正模。揭示了高次模对单分子动力学和分子间半持久纠缠产生的影响。数值模拟是在镜腔上的纳米粒子内进行的，类似的系统具有小面形状的形态变化，使它们成为室温纠缠产生和量子技术的理想选择。

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.