Effect of waveguide wall roughness on quantum signal transmission

Given the undeniable advantages of quantum computers, several methods have been proposed to create compact and versatile quantum systems. Among these methods, integrated quantum optics processors have garnered significant attention, leading to the proposal of various quantum-based optical devices. Since the advent of quantum computers, incoherence in qubit processes has posed a challenge, manifesting in numerous forms. This incoherence results in changes and distortions of system states during processing. While quantum optical systems have advantages over conventional technologies, they are not immune to this issue. In our research, we demonstrate that random imperfections in waveguide walls during manufacturing (etching) can be a major source of decoherence in quantum optical devices, potentially distorting quantum states over medium to long distances. We compare various semiconductor materials and fabrication technologies and find out that InP/InGaAsP, SiON, Si₃N_4, and silica are suitable materials for fabricating quantum waveguides. In contrast, the silicon-on-insulator (SOI) platform has quantum crosstalk lengths of only 1 mm and 180 microns for 50 and 30% coupling as the minimum and maximum threshold conditions, respectively. Using conventional fabrication methods could lead to short quantum crosstalk lengths and hinder quantum processing capabilities. Hence, precise methods must be employed to effectively fabricate waveguides using SOI technology. Based on the decoherence properties, this work determines the appropriate quantum-grade platforms for devices utilized in quantum processing.