Arend G. Dijkstra

Non-Markovian Entanglement Dynamics in the Presence of System-Bath Coherence

A complete treatment of the entanglement of two-level systems, which evolves through the contact with a thermal bath, must include the fact that the system and the bath are not fully separable. Therefore, quantum coherent superpositions of system and bath states, which are almost never fully included in theoretical models, are invariably present when an entangled state is prepared experimentally. We show their importance for the time evolution of the entanglement of two qubits coupled to independent baths. In addition, our treatment is able to handle slow and low-temperature thermal baths.

Correlated fluctuations in the exciton dynamics and spectroscopy of DNA

The absorption of ultraviolet light creates excitations in DNA, which subsequently start moving in the helix. Their fate is important for an understanding of photodamage, and is determined by the interplay of electronic couplings between bases and the structure of the DNA environment. We model the effect of dynamical fluctuations in the environment and study correlation, which is present when multiple base pairs interact with the same mode in the environment. We find that the correlations strongly affect the exciton dynamics, and show how they are observed in the decay of the anisotropy as a function of coherence and population time in a nonlinear optical experiment.

The role of the environment time scale in light-harvesting efficiency and coherent oscillations

We study the efficiency of exciton transport as a function of the typical reorganization time scale of the environment using the hierarchy of equations of motion. As a model system, we choose the Fenna?Matthews?Olson (FMO) complex. An environment in which the dynamics is not much faster than the system leads to prolonged quantum coherent transport, even at room temperature. We find that this does not make the transport process more efficient for standard FMO parameters, but does increase the efficiency in the case when exciton decay competes with trapping at the reaction center. We furthermore find that initial correlations do not influence population oscillations.

Non-Markovianity: initial correlations and nonlinear optical measurements

By extending the response function approach developed in nonlinear optics, we analytically derive an expression for the non-Markovianity in the time evolution of a system in contact with a quantum mechanical bath, and find a close connection with the directly observable nonlinear optical response. The result indicates that memory in the bath-induced fluctuations rather than in the dissipation causes non-Markovianity. Initial correlations between states of the system and the bath are shown to be essential for a correct understanding of the non-Markovianity. These correlations are included in our treatment through a preparation function.

System Bath Correlations and the Nonlinear Response of Qubits

In this letter we study qubits coupled to the bath formed by their environment. Although entanglement of the qubits is a well-known topic, much less effort has gone into the description of the correlations between the qubits and the bath. Here, we investigate these correlations, and study their effect on the qubits in equilibrium and their dynamics following the interaction with one or several external pulses. We find that a correct description of the correlations at the moment of these interactions is essential for a correct understanding of the dynamics.