The way that we traditionally use external stimuli is as observational tools that offer insights into the workings of the molecular world. In fact, most of the things we know about molecules we have learned by determining the way that they respond to chemical, electromagnetic or mechanical perturbations. The interest in our group is in exploring, using theoretical tools, an additional facet of the molecular response to external stimuli: its use as an active control tool to manipulate the properties and dynamics of matter in intriguing and potentially useful ways.
The research program of our group is structured around two main thrusts:
1. Laser control of electrons
We investigate the fundamental limits in the laser control of electrons and electronic properties in matter by exploiting quantum mechanical effects, an area of research known as quantum control. The reason to focus on lasers over more conventional means (e.g., an applied voltage, or changes in thermodynamic control variables) is that lasers offer the possibility of dynamic manipulation on an ultrafast timescale. We investigate, for instance, the microscopic origin of the fastest existing method for the generation of currents, and the ability of lasers to turn insulating materials into transient metals. In addition to its interest at a fundamental level, pushing the time limit in which electronic properties can be controlled has the potential to catalyze transformative progress in chemistry, spectroscopy, optoelectronic device design, communication through electrical signals, and any other science or technology based on electronic properties and their control.
In order to explore this venue of control, we use theoretical models and numerical simulations of the quantum-classical or fully quantum dynamics of nanoscale systems under the influence of external stimuli as means to identify possible mechanisms for control and to quantify the extent of control that can be achieved.
2. Mechanical manipulation of single-molecule junctions.
In recent years a number of techniques have been developed that allow us to access the properties of single molecules. Our group investigates the integration of two prominent single-molecule techniques –single-molecule pulling and molecular electronics– as a rich test-bed for chemistry and physics at the nanoscale, and the basis for novel multi-dimensional single-molecule spectroscopies. In this class of measurements, forces and voltages are simultaneously applied to a single molecule in a metal-molecule-metal junction. A great challenge for theory is to correctly describe the complex interplay between the elastic and the electric properties of single molecules, and to capture the statistical variations in molecular conformation and junction geometry observed in and between experiments. Our group develops the theoretical and computational technology required to describe this class of experiments atomistically and further the information content that can be extracted from such measurements, with the goal of helping this direction mature into a general and highly discriminating multi-dimensional spectroscopy for molecules.