What The goal of the project is to develop more efficient and accurate approximations for modelling the effects of quantum noise. Quantum noise is the uncontrolled influence from the surrounding environment that inevitably affects a microscopic system of interest, such as an atom or electrons in a solid. On these microscopic scales, the laws of nature appear fundamentally different from how we perceive them in our everyday lives – rather than Newton’s laws, nature obeys the laws of quantum mechanics. These laws are formulated for isolated systems, and only approximate methods exist for describing the effects of quantum noise on a physical system. Why Several scientific challenges of the 21st century require better methods for modelling the effects of quantum noise. New tools are for instance needed to develop more efficient photovoltaics, understand the mechanism of photosynthesis, and develop scalable platforms for quantum information processing. Today’s standard methods for modelling quantum noise were developed in the middle of the 20th century for simple quantum systems such as individual atoms or nuclei. While successful for the scientific problems studied at the time, these methods fail when applied to complex quantum systems that we encounter today. How Recently, my collaborators and I developed a new approach to modelling quantum noise, which can be applied to far more complex systems than historical approaches. Our method significantly improves the efficiency at which one can describe the effects of quantum noise on systems weakly coupled to their environment. In this project, I seek to generalize our approach to the important, but challenging, case of strong coupling. While this problem has been studied extensively, the success of our method in the weak-coupling regime indicates a significant potential for further progress by applying our approach here. As a secondary line of study, I will seek to gain new insights by applying our new method to current scientific problems that involve complex quantum systems weakly coupled to their environment.