Modelling open quantum systems beyond weak-coupling regimes

Lead Research Organisation: University of Manchester
Department Name: Physics and Astronomy


There has been a recent rapid development in experimental capabilities to probe and control larger and more complex quantum systems. Such systems tend to interact strongly with their environments, which invalidates standard theoretical approaches that relay on weak-coupling approximations. This project will develop new theoretical techniques to study the strong system-environment coupling regime, and apply them to understand the behaviour of both solid state and molecular nanosystems


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McConnell C (2019) Electron counting statistics for non-additive environments in The Journal of Chemical Physics

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1793836 Studentship EP/N509565/1 01/10/2016 30/06/2020 Conor McConnell
Description Over the course of the past two and a half years we have been interested in modelling open quantum systems beyond weak-coupling regimes. Our main motivation in doing so is to be able to model and explain the flow of electrons within molecular nanojunctions. A molecular nanojunction is the term used to describe a component of an electrical circuit (such as a resistor) which is built at a molecular level and is consider as being a singular molecule coupled to two electrodes.

In this set-up it is common to consider a system which has been coupled to various different environments, including the two electrodes and the effect of vibrations within the molecule. We have spent the past few years considering the effect of these vibrations and accurately modelling the impact which strong vibrations would have on the system of interest. We have furthermore shown that in order to accurately calculate the current flow, power output or efficiency of these systems one must consider all three environments as having "knowledge" of this strong vibrational coupling (which we call the non-additive treatment). In previous works people have considered the three environments separately, and we have shown that this treatment results in inconsistencies in several regimes and even breaks down completely in some.
Exploitation Route In the future our work could be applied to systems with strong coupling to the electrodes as well as the vibrational environment. So far we have considered spectral densities which are quite fundamental and so a physically motivated spectral density would be interesting to consider. The use of the reaction co-ordinate technique, to model these strong interactions non-additively, is of use in all areas of open quantum systems ranging from thermodynamics to photovoltaics.
Sectors Education,Electronics,Manufacturing, including Industrial Biotechology