Strong Field Quantum Control

Stanford University, Stanford CA

Investigators

Abstract

The motion of electrons and atoms during and immediately following their interaction with light fields is one of the important and difficult challenges of quantum physics. The standard methods of quantum calculations that underpin most current understanding of molecular structure are based on simplifying assumptions that break down at critical times when molecules absorb intense light, collide strongly, or are subjected to other strong electric fields. Without these simplifications, the calculations become intractable even for molecules of modest size, and the basic connections between atomic motion and electron motion in molecules are not well understood. The goal of the quantum control research in this project is to use strong fields to direct quantum processes towards desired targets, such as rearranging the bonds in a molecule. Control methods using strong fields can overcome the complexities described above, through the use of powerful techniques such as learning feedback algorithms that automatically reprogram the experimental driving fields to seek to optimize the target yield without guidance from calculations. This project explores three new ways to improve the effectiveness of quantum control. The first is a new conceptual framework called a Quantum Resonance Ring that could help our understanding of many-body quantum problems. The second improvement is to apply the techniques of pattern recognition to the high-dimensional problems in quantum control. The third improvement is to extend laser control investigations to use newly available x-ray laser sources. In a broader context, quantum control research will ultimately lead to a better understanding of the actions of electrons in molecular transformation and chemistry. Electron motion is considered a gateway problem for progress in areas of nano-materials, chemical science, and energy technologies. Insights gained from this work could therefore influence problems such as the energy conversion efficiency of new photovoltaics; the search for a catalyst to efficiently extract hydrogen from water; or the development of sustainable biofuel technologies. Quantum control is also the fundamental technology in the new field of quantum information. Future scalable quantum computers or quantum information transfer systems will rely on quantum control for gate operations and for error correction. Some of the most promising implementations involve the use of electrons as qubits and lasers as control fields, so the knowledge gained about quantum control of electrons in the presence of strong laser fields could be directly applicable.