Ultrafast Control of Electrons Using Few-Cycle Laser Pulses

The latest advances in laser technology now enable the generation and control of few-cycle lasers in the IR and UV/Vis. Using them it is now possible to apply laser fields with intensities of 1013-1014 W/cm2 before the emergence of dielectric breakdown. At those intensities the incident light can dramatically distort the electronic structure of nanoscale systems and bulk matter thus opening unprecedented opportunities to manipulate electronic properties and dynamics on a femto to attosecond timescale. In this thesis, we investigate general strategies for the control of matter at the level of electrons using few-cycle laser. First we introduce a control scenario based on the Stark effect that we call SCELI, which is short for the "Stark Control of ELectron dynamics at Interfaces". The scenario uses the Stark effect induced by non-resonant light of intermediate intensity (non-perturbative but non-ionizing) to create transient resonances among the energy levels of two adjacent materials. These transient resonances open quantum tunneling pathways for interfacial charge transfer that are otherwise forbidden in undriven systems, thus providing key opportunities for the ultrafast control of electrons in matter. SCELI is of general applicability and we computationally demonstrate it by following the quantum dynamics driven by non-resonant laser pulses along semiconductor-semiconductor and molecule-semiconductor interfaces. As shown, SCELI is robust to decoherence, changes in the laser frequency and amplitude, energy level alignments between the materials of the heterojunction and survives even in the presence of interfacial band bending and electromagnetic screening. We demonstrate how to use SCELI to turn an insulating heterojunction into a conducting one on a femtosecond timescale, to generate phase controllable currents in the absence of bias voltage and to induce interfacial charge transfer when resonant routes are not available and/or in timescales faster than those offered by resonant routes. This collection of results demonstrate the general utility of Stark based strategies for the control of electrons. Second, we unveil a general mechanistic feature in emerging experiments that employ few-cycle lasers to generate currents on femtosecond timescale in nanojunctions and that have lead to the birth of the field of petahertz electronics. Through a theory-experiment collaboration, in the context of atomically thin semimetal graphene coupled to metallic electrodes, we demonstrate that the optical generation of currents has contributions arising from the photogeneration of real and virtual charge carriers. Further, we isolate carrier-envelope signatures of each contribution that allow decomposing the observed current into these two components. These advances offer direct means to optically monitor these charge carriers as needed for the design of future lightwave petaherz electronics