Nanoscale Coherent Control. Ultrafast dynamics of single molecules, individual light harvesting complexes and discrete nanoantennas at room temperature.
Authors:   , Brinks Daan 
Published: October 2023

Ultrafast pulses allow observation of molecular dynamics with femtosecond time resolution through pump probe
experiments. However, averaging over an ensemble of molecules tends to wash out phase sensitive information, necessary
to probe quantum effects, due to the intrinsic inhomogeneity in molecular conformations, orientations and interactions that
lead to unique potential energy landscapes for each molecule.
It is therefore important to go beyond the ensemble average when looking at quantum dynamics of organic systems at room
temperature, and resolve the behaviour of specific molecules on an individual basis.
In this thesis, we show the creation, manipulation and observation of ultrafast coherent effects in single molecules at room
temperature, and resolve a certain measure of environmental influence on the specific dynamics of each molecule. Moreover,
we apply this insight to investigate a functional light harvesting biosystem, and lay the basis for a technique that has the time
and space resolution required to observe these systems in vivo.
In chapter 1, we introduce the concepts and techniques the research in this thesis is built on.
In chapter 2, we treat the possibility of controlling ultrafast pulses at the high-NA diffraction limit, and come to conclusions
about the procedure to follow there that hold for all pulse-shaping experiments. We show in proof of principle experiments
that we can control the ultrafast characteristics of optical pulses in nanometric excitation volumes.
In chapters 3 and 4 we report the creation, detection and control of ultrafast quantum dynamics in single organic molecules at
room temperature. We show that manipulation of superposition states is possible in these systems within a coherence
dephasing time of ~50 fs. This leads to the first observation of rabi-oscillations in room temperature single molecules, to
ultrafast operation of an organic qubit, and to the creation of non-stationary superposition states (vibrational wavepackets).
We probe the influence of the local environment on the composition and dynamics of these wavepackets and show we can
optimize the state preparation protocol for each individual molecule in its own nanoenvironment, leading to high fidelity
coherent control. In these chapters we lay out the proof of principle work of detecting the quantumdynamics of a complex
system in interaction with its environment at room temperature.
In chapter 5 we discuss application of these techniques to the investigation of long lived coherence in photosynthetic
systems. We show that electronic coherence between different rings of the LH2 system persists to time scales of 100s of
femtoseconds at room temperature. Moreover we show that the energy transfer pathways in LH2 adapt to environmentally
induced changes in the molecule and that the nature of the transfer remains coherent for each pathway, providing strong
evidence that coherent energy transfer is the optimum process for energy transfer in photosynthesis.
Finally, in chapter 6 we take the technical development one step further and report on the creation of a framework based on
plasmonic antennas that allows for control of the amplitude-phase characteristics in nanometric sized hotspot fields. We
show for the first time that the ultrafast characteristics of plasmonic hotspots can directly be engineered through design of the
plasmonic system and experimentally demonstrate two much-anticipated examples: a sub-diffraction resolution phase
shaper and an ultrafast plasmonic switch for pump probe experiments.
The results presented in this thesis form the first creation and observation of ultrafast coherent dynamics in individual
molecular systems at room temperature. This is a necessary step to be able to do true quantum tomography in complex
systems, resolve the influence of the environment on molecular dynamics, and investigate the physics that determines
evolutionary optimization and functionality in biomolecules.