Research Projects

Photonic systems such as one dimensional optical waveguide arrays and coupled resonators have emerged as a promising platform to engineer the behavior of light leading to several valuable technological developments. However, disorder is known to have a significant detrimental impact on the transport of light in photonic systems. Because of their novel features, topological photonics is rapidly emerging as a field of research for designing and controlling the behaviour of light in a robust manner and provides solution to these issues. Topological invariants provide intrinsic protection against specific classes of disorder. In particular, topological effects in optical waveguide arrays have demonstrated resilience to disorder, making them appealing for applications in a variety of fields at both classical and quantum levels. However, realistic quantum systems are inevitably open and interact with their surroundings, which results in decoherence. Until recently, the majority of studies on the physics of topological photonic systems involved Hermitian models. We examine the issue of decoherence in topological waveguide array system by considering loss of waveguide modes. Decoherence effects are a significant barrier to maintaining quantum coherence and entanglement. Although topological protection can mitigate disorder effects, it is an open and pressing question how effective it is when decoherence mechanisms like photon loss, phase noise, and thermal fluctuations are present. Some lossy quantum systems can be described by non-Hermitian Hamiltonians, which enables an analysis akin to that of closed systems. Although this approach has produced some intriguing insights, non-Hermitian Hamiltonians describe the dynamics of open quantum systems only in the short-time regime before the quantum jumps occur. The full dynamics is more accurately described by the Lindblad Master Equation. More specifically, unlike closed quantum systems, open systems are not described by their Hamiltonian alone but, in addition, include Lindblad operators, which describe the influence of the environment. Through the development of analytical models and numerical simulations, the project will investigate the effects of decoherence, on edge mode stability, localization, and transport features. We aim to systematically examine the impact of decoherence in topological quantum photonic systems, to identify regimes and protocols where topological features can enhance the robustness of quantum coherence and entanglement in open photonic systems. Most of the earlier works have focused on the Su–Schrieffer–Heeger model (SSH) model. Here we consider two topological models which have been realised in photonic waveguide arrays, namely: one dimensional Aubry-André-Harper model and higher-order breathing Kagome model. More specifically, we study the Aubry-André-Harper and higher-order breathing Kagome lattice topological system under decoherence, and explore the boundaries and processes of topological protection in quantum photonic waveguide arrays. By considering these models we systematically compare the robustness of one dimensional and two dimensional topologies under decoherence. We employ the master equation formalism to describe the system of topological waveguide arrays interacting with the environment. The results will help us better understand topological resilience in open quantum photonic systems and offer important information for creating fault-tolerant quantum photonic devices. Although we focus on waveguide arrays system, our work will also be applicable to the analysis in other platforms, including superconducting circuits, photonic crystal, and nano-mechanical systems where topological models have recently studied.