A pulse-shaping algorithm for a matter wave with the purpose of controlling a binary reaction has been designed. The scheme is illustrated for an Eley-Rideal reaction where an impinging matter-wave atom recombines with an adsorbed atom on a metal surface. The wave function of the impinging atom is shaped such that the desorbing molecule leaves the surface in a specific vibrational state.
A pulse-shaping algorithm for a matter wave with the purpose of controlling a binary reaction has been designed. The scheme is illustrated for an Eley-Rideal reaction where an impinging matter-wave atom recombines with an adsorbed atom on a metal surface. The wave function of the impinging atom is shaped such that the desorbing molecule leaves the surface in a specific vibrational state.
In this article we discuss possibilities for manipulating a matter wave with time-dependent potentials. Assuming a specific setup on an atom chip, we explore how one can focus, accelerate, reflect, and stop an atomic wave packet, with, for example, electric fields from an array of electrodes. We also utilize this method to initiate coherent splitting or an arbitrary wave form. Special emphasis is put on the robustness of the control schemes. We begin with the wave packet of a single atom and extend this to a Bose-Einstein condensate in the Gross-Pitaevskii picture. In analogy to laser pulse shaping with its wide variety of applications, we expect this work to form the base for more complex time-dependent potentials, eventually leading to matter-wave pulse shaping with numerous applications.
Coherent control of light and matter is a major tool in current atomic physics and physical chemistry research. Technological advances in ultrafast laser pulse shaping allow control over the dynamics of molecular systems on sub-picosecond timescales. This thesis demonstrates feedback control over a variety of quantum systems and describes an adaptive genetic algorithm used in the experiments. In the gas phase, we examine control of multi-photon, dissociative ionization in diatomic sodium. The learning algorithm achieves control over the dissociative fraction primarily by adjusting the peak intensity of the laser field. We also investigate control of multi-mode stimulated Raman scattering in liquid phase methanol. Analysis of the results leads to identification of quasi-impulsive Raman coupling as a possible control mechanism. Further experiments, combined with numerical simulations of the interaction, demonstrate that an impulsive coupling of the two modes by the pump pulse can control the Raman gain. We extend the Raman control experiments to ethanol and isopropanol. Finally we apply feedback control techniques in an initial investigation of a liquid-phase chemical reaction. Specifically, we examine the ring-opening conversion of cyclohexadiene into hexatriene. The reaction dynamics occur on an excited state potential energy surface. Through control of the excitation pulse shape, we seek to guide the wavepacket evolution on the excited state to exert control over the reaction branching ratio.
Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the quantum degenerate regime, where atoms and molecules form coherent matter waves, reactions are theoretically described by nonlinear mixing of matter-wave fields. In this scenario, we expect phase matching between reactants and products, analogous to the mixing of photonic fields in nonlinear optics. Here we report on the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter-wave diffraction with optical lattices, we verify spatial coherence of both atoms and molecules and observe phase doubling when atomic waves combine into molecular waves, the matter-wave analogue of optical frequency doubling. The diffraction patterns further reveal two-atom entanglement generated during the reaction. Our observations establish phase coherence and entanglement generation as two essential features of "quantum many-body chemistry". Moreover, our work opens a pathway to control of reaction dynamics by manipulation of matter-wave phases.
Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the classical regime, reactions are expected to proceed faster at high temperatures and slow to a halt in the zero-temperature limit according to Arrhenius kinetics. In the quantum degenerate regime, where bosonic atoms and molecules form coherent matter waves, reactions are instead described by nonlinear mixing of matter-wave fields, leading to collectively-enhanced reaction rates and coherent amplification. This raises the question: how does the matter-wave phase evolve during a reaction, and how can it influence reaction dynamics? In the quantum regime, the matter-wave phases of the reactants and products are expected to match through wave mixing, analogous to phase matching of photonic fields in nonlinear optics.\par We report the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter wave diffraction with optical lattices, we verify spatial coherence of both reactants and products and observe phase doubling when atomic waves combine into molecular waves - the matter-wave analogue of second-harmonic generation. The diffraction patterns also reveal distinct signatures of entanglement generated between reacting particles as the reaction is initiated. Our observations establish phase coherence and entanglement as two essential features of "quantum many-body chemistry" where macroscopic quantum fields govern the reaction dynamics.
Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the classical regime, reactions are expected to proceed faster at high temperatures and slow to a halt in the zero-temperature limit according to Arrhenius kinetics. In the quantum degenerate regime, where bosonic atoms and molecules form coherent matter waves, reactions are instead described by nonlinear mixing of matter-wave fields, leading to collectively-enhanced reaction rates and coherent amplification. This raises the question: how does the matter-wave phase evolve during a reaction, and how can it influence reaction dynamics? In the quantum regime, the matter-wave phases of the reactants and products are expected to match through wave mixing, analogous to phase matching of photonic fields in nonlinear optics.\par We report the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter wave diffraction with optical lattices, we verify spatial coherence of both reactants and products and observe phase doubling when atomic waves combine into molecular waves - the matter-wave analogue of second-harmonic generation. The diffraction patterns also reveal distinct signatures of entanglement generated between reacting particles as the reaction is initiated. Our observations establish phase coherence and entanglement as two essential features of "quantum many-body chemistry" where macroscopic quantum fields govern the reaction dynamics.
Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the classical regime, reactions are expected to proceed faster at high temperatures and slow to a halt in the zero-temperature limit according to Arrhenius kinetics. In the quantum degenerate regime, where bosonic atoms and molecules form coherent matter waves, reactions are instead described by nonlinear mixing of matter-wave fields, leading to collectively-enhanced reaction rates and coherent amplification. This raises the question: how does the matter-wave phase evolve during a reaction, and how can it influence reaction dynamics? In the quantum regime, the matter-wave phases of the reactants and products are expected to match through wave mixing, analogous to phase matching of photonic fields in nonlinear optics.\par We report the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter wave diffraction with optical lattices, we verify spatial coherence of both reactants and products and observe phase doubling when atomic waves combine into molecular waves - the matter-wave analogue of second-harmonic generation. The diffraction patterns also reveal distinct signatures of entanglement generated between reacting particles as the reaction is initiated. Our observations establish phase coherence and entanglement as two essential features of "quantum many-body chemistry" where macroscopic quantum fields govern the reaction dynamics.