Theory of quantum control of atomic/molecular ensembles by ultrafast electromagnetic fields

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Quantum control involves the precise manipulation of the dynamics of quantum states using tailored electromagnetic fields in order to achieve a desired goal. In recent experiments such as high-harmonic generation from clusters, and ultrafast studies of organic photovoltaics, femtosecond electromagnetic fields are used to drive, probe or control ensembles of atoms or molecules. The physics of these ensembles can neither be described by few-body models, nor by bulk classical or semi-classical models. Also, these ultrafast optical interactions are both nonlinear and non-perturbative, making their theoretical description challenging. This proposal explores this new frontier in quantum control, namely, the control of dense ensembles of a large number (~5000) of atoms or molecules over ultrashort (few femtosecond) timescales. Our objectives are to investigate the quantum dynamics of dense quantum ensembles driven by ultrafast pulses, to elucidate the fundamental mechanisms in their control, and to establish the key parameters that optimize the control process. We will develop and evaluate quantum control techniques, and design new protocols for the optimization of desired targets in realistic physical systems such as high-harmonic generation from atomic clusters. Ultimately, we intend that the techniques and protocols that we develop will be exploited by experimental researchers in ultrafast science to more accurately predict and implement control schemes that optimize atomic and molecular processes such as ultrafast scattering and high harmonic generation in dense ensembles. In the past 3 years, we have developed a theoretical and computational methodology that describes the quantum dynamics of quantum ensembles accurately over a range of ensemble densities, while simultaneously being a method that is reasonable in computational cost and time. Building on this, theoretical models of high-harmonic generation in atomic clusters, and numerical algorithms required to describe the quantum control of non-perturbative phenomena in quantum ensembles will be developed and implemented on supercomputing clusters. With NSERC support, we will build on this work to develop protocols for the optimization of desired target properties of the ensemble, for example, to suppress or enhance ensemble dephasing or spontaneous emission, or to shape the spectrum of the radiation emitted from driven ensembles. The novelty of this work is the development of theoretical models of ultrafast quantum control in many-body systems of atoms or molecules, which are problems that are more complex than ever before. The lines of investigation address theoretical/computational problems at the forefront of our understanding of open control systems, with strong ties to current and proposed leading experiments. The results of this discovery research will be used to support the applied aspects of my research program in biosensors and solar cell technology.