Coherent Control of Cold Collision by Preparing Molecular Eigenstates Using Stark-Induced Adiabatic Passage

General audience abstract:

This project focuses on developing a comprehensive understanding of the quantum mechanical processes that drive molecular interactions including chemical reactions at the most fundamental level. The main goal of this research is to explore the character of quantum systems and improve our ability to manipulate them, which is of great importance in various applications including realization of a quantum computer.

The research team will carry out low energy (cold) collision experiments with molecules prepared in well-defined quantum states. By correlating the quantum states of the incoming particles with those of the outgoing particles they will explore the quantum mechanical interactions involved in making and breaking chemical bonds. This research combines cutting edge quantum optical techniques and expertise in laser spectroscopy with state-resolved collision dynamics using a supersonically expanded molecular beam.

The graduate students involved in this project will learn the technical skills needed for multiphoton laser spectroscopy using vacuum ultraviolet laser pulses, quantum state preparation using sophisticated single-mode pulsed laser systems, and manipulation of a supersonic beam. Additionally, the research team will design a high resolution mass spectrometer to resolve the scattering angular distribution in cold collisions.

This comprehensive training in broad areas of quantum physics and chemistry will help to prepare the students to be leaders in improving the science and technology of tomorrow. Technical audience abstract:

To understand the quantum mechanical processes involved in chemical reactions, it is essential to find a direct correspondence between experimental measurements and theoretical calculations. To achieve this goal, experimentalists need to select theoretically tractable molecules like H2 (N2, CO, etc.), which are also of relevance to current science. The researchers will prepare diatomic molecules in high vibrational states using a coherent optical technique called multi-step Stark-induced adiabatic Raman passage (multi-step SARP).

Multi-step SARP is a generalization of the SARP process developed earlier by this research group, which can pump a large ensemble of H2 molecules to a variety of vibrationally excited levels. Multi-step SARP will combine two or more SARP processes to achieve near complete population transfer to a very highly vibrationally excited level. The researchers have shown theoretically that by combining several Stokes pulses on the wing of a stronger pump pulse it is possible to reach very high vibrational states.

Long term prospects for this technique include preparing the highest vibrational level of H2 and even reaching the vibrational dissociation continuum, generating a pair of entangled loosely bound H atoms. These exotic quantum systems will allow the researchers to overcome the reaction barrier in cold and ultracold collisions and test fundamental quantum physics principles, such as interference in collision.

The first goal of the project is to set up the multi-step SARP experiment and demonstrate the preparation of very high vibrationally excited levels of H2. Selection of the laser polarization used in the multi-step SARP will permit control of the alignment of the bond axis of the highly vibrationally excited molecules. Excitation of very high vibrational states using a two-step SARP process will be a major leap forward in the study of cold molecular collisions.

Once prepared the researchers will carry out cold scattering experiments on the four-center reaction H2 + D2 →2HD in a supersonically expanded mixed beam of H2 and D2. The collision dynamics of highly vibrationally excited H2 molecules are of immense interest for understanding and modelling the physics and chemistry of the interstellar medium. Additionally, high-lying vibrational levels of H2 are considered essential to the efficient generation of H- beams by dissociative attachment of low energy electrons, which has important applications in igniting a fusion reactor.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.