Light-Matter Interaction in Nano-Photonic Systems: Harnessing the Weakly Interacting Emitter-Cavity System for Controlling Single Photon Emission

Abstract

This thesis investigates the light-matter interaction of the quantum-electrodynamic system that consists of a quantum emitter weakly interacting with a nanophotonic cavity, in order to control single-photon emission through the cavity's mode. State-of-the-art single-photon sources that are used to generate nonclassical states of light rely on strong interaction between the emitter-cavity system. This strong light-matter interaction between the two-state quantum emitter and the cavity achieves single-photon nonlinearity in the cavity's mode, such that a cavity populated with a single-photon state will repel a subsequent photon upon excitation, a mechanism often referred to as photon blockade. Thus, the cavity transmits one photon at a time. This study's principal result as presented in Chapter 2 is that photon blockade can be achieved in a cavity that is weakly interacting with a two-state quantum system, when the cavity is excited by the field of a weakly interacting scattering emitter. The scattering emitter is pumped by a laser and energy flows from the emitter to the cavity. However, the contrasting loss rates of energy dissipation between the ``lossy'' scattering emitter and the ``low-loss", high-quality cavity yields a Fano interference, such that at the Fano antiresonant frequency, photons are blocked from flowing through the scattering emitter into the cavity. Thus the cavity populated with a single-photon state, from weak interaction to a two-state quantum system, experiences photon blockade when excited through weak interaction with a scattering emitter under a pump-laser operating at the Fano antiresonance. This result of photon-blockade through the Fano interference mechanism is novel because it operates in the weak light-matter interaction regime, for a cavity with a linear response. This study shows that this photon blockade through the Fano interference mechanism is akin to the so called non-Hermitian photon blockade, which we generalize, and is also related to the quantum interference mechanism of the unconventional photon blockade that has been demonstrated for systems having a large degree of nonlinear response through strong intra-cavity interactions; fundamental to such systems is the cooperativity factor--that is the ratio between the light-matter interaction to the rates of energy's dissipation of the emitter-cavity system. This cooperativity factor must be greater than one, a prerequisite for photon-blockade via quantum interference. The ability of nanophotonic cavities to confine and store light to nanoscale dimensions also has important implications for enhancing molecular, excitonic, phononic, and plasmonic optical responses. Spectroscopic signatures of processes that are ordinarily exceedingly weak such as pure absorption and Raman scattering have been brought to the single-particle limit of detection, while new emergent polaritonic states of optical matter have been realized through coupling material and photonic cavity degrees of freedom across a wide range of experimentally accessible interaction strengths. Chapters 3 and 4 present both optical and electron beam spectroscopies of cavity-coupled material systems in different light-matter interaction regimes, which provides a theoretical basis for understanding the physics inherent to each, and highlights recent experimental advances and exciting future directions.