Quantum Control in Two-Dimensional Fourier Transform Optical Spectroscopy

The ability of controlling the evolution of quantum systems by applying interaction with shaped laser pulse, known as coherent control or quantum control, has attracted significant interest in many fields of researches over the last two decades. Coherent control has been applied to photo-induced selective chemical reaction processes, controlling the direction of electron motions in semiconductors, multi-photon excitation fluorescence microscopy, and the optimization of nonlinear light-matter interactions. Quantum systems subjected to control have been ranged from atoms and molecules to semiconductors and biological samples. Especially, great efforts have been devoted to managing the transition probabilities between quantum states in atomic systems. Previous transition probability controls are mostly restricted to a ladder-type system. The controlled transition in a ladder-type system is readily monitored by detecting the fluorescence decay from a target excited state. On the other hand, the two-photon transition between the excited states in a V -type quantum system is not straightforward to measure, and thus has been difficult to control. It is because the state population of the target excited state is coherently mixed with the dominant one-photon transition population from the ground state. This difficulty is overcome, in this thesis, with the combined use of two-dimensional Fourier-transform optical spectroscopy and a coherent control technique. In this thesis, we present a new method that harnesses coherent control capability to two-dimensional Fourier-transform optical spectroscopy. For this, three ultrashort laser pulses are individually shaped to prepare and control the quantum interference involved in two-photon inter-excited state transitions of a V -type quantum system. In experiments performed with atomic rubidium, quantum control for enhancement and annihilation of 5P1/2 → 5P3/2 transition is successfully tested, where the engineered transitions are distinguishably extracted in the presence of dominant one-photon transitions. Experiments for quantum interference engineering have revealed that the target transition strength is tripled in spectral phase-shaping, and enhanced by 60% in spectral amplitude shaping. Also, we show that the conventional coherent transients in a simple two-level system is mimicked by two-photon coherent control in a V -type three-level system. Here, higher order chirps of a shaped laser pulse play the roles of time and linear chirp in coherent transients. In a three-pulse coherent control experiment of atomic rubidium, the phase and amplitude of controlled transition probability is retrieved from a 2D Fourier-transform spectral peak. Finally, we propose the application of the novel coherent control technique or advanced two-dimensional Fourier transform spectroscopy to semiconductor quantum well systems. For this, we have considered semiconductor heterostructures made of III-V compounds for the V -type three-level systems along with numerical calculations. It is hoped that the devised coherent control for excited-state transitions become useful in untangle the unknown nature of chemical and biological reaction processes.