Information transfer in open quantum systems

Abstract

This thesis covers open quantum systems and information transfer in the face of dissipation and disorder through numerical simulation. In Chapter 3 we present work on an open quantum system comprising a two-level system, single bosonic mode and dissipative environment; we have included the bosonic mode in the exact system treatment. This model allows us to gain an understanding of an environment’s role in small energy transfer systems. We observe how the two-level system-mode coupling strength and the spectral density form characterising the environment interplay, affecting the system’s coherent behaviour. We find strong coupling and a spectral density resonantly peaked on the two-level system oscillation frequency enhances the system’s coherent oscillatory dynamics. Chapter 4 focusses on a physically motivated study of chain and ladder spin geometries and their use for entanglement transfer between qubits. We consider a nitrogen vacancy centre qubit implementation with nitrogen impurity spin-channels and demonstrate how matrix product operator techniques can be used in simulations of this physical system. We investigate coupling parameters and environmental decay rates with respect to transfer efficiency effects. Then, in turn, we simulate the effects of missing channel spins and disorder in the spin-spin coupling. We conclude by highlighting where our considered channel geometries outperform each other. The work in Chapter 5 is an investigation into the feasibility of routing entanglement between distant qubits in 2D spin networks. We no longer consider a physical implementation, but keep in mind the effects of dissipative environments on entanglement transfer systems. Starting with a single sending qubit-ancilla and multiple addressable receivers, we show it is possible to target a specific receiver and establish transferred entanglement between it and the sender’s ancilla through eigenstate tunnelling techniques. We proceed to show that eigenstate tunnelling-mediated entanglement transfer can be achieved simultaneously from two senders across one spin network.