Quantum Control of Electron-Hole Wave Packets in Semiconductor Nanostructures with Strong Terahertz Pulses

Oregon State University, Corvallis OR

Investigators

Abstract

****Technical Abstract**** This research addresses a fundamental question of light-matter interactions in condensed matter: How do quantum states in semiconductors evolve in the presence of strong electromagnetic waves? Quantum dynamics of intraband transitions (low-energy excitations of 1-10 meV) in semiconductors are little explored to date; the objective of this project is to establish concrete physical pictures of how the quantum dynamics unfold in a many-electron system. Interacting with electron-hole (e-h) wave packets in semiconductor nanostructures, strong terahertz (THz) pulses induce intraband transitions occurring on a picosecond time scale. Ultrafast optical/THz probe pulses resolve not only the amplitude but also the phase of the quantum states in the time domain so that the quantum dynamics can be completely mapped out. Given that Coulomb interactions govern the quantum dynamics, the time-resolved THz study will provide a novel opportunity to understand Coulomb correlations in the e-h system and decoherence of many-body excitations. As the THz intensity exceeds a certain level, the nature of light-matter interactions will undergo a qualitative transition showing traits of the field-induced motion of electrons and holes. This will set a unique stage to observe the quantum-to-classical transition of light-matter interactions in condensed matter. The outreach programs include optics demonstrations for K-12 students, research experience for high school students, and professional development opportunity for science and math teachers. ****Nontechnical Abstract**** Terahertz (THz) waves are electromagnetic waves whose frequencies lie between the microwave and infrared regions. Naturally occurring THz radiation fills up the space of everyday life providing warmth, yet this part of the electromagnetic spectrum remains the least explored region. THz science and technology is a new and exciting frontier with a broad range of applications. For example, the unique and advanced techniques of THz spectroscopy have been proved to be a powerful tool to investigate the material properties inaccessible until recently. Interacting with a semiconductor, light can create oppositely charged particles, called electrons and holes. When the optical transition occurs near the energy band gap, the attractive interaction between the charged particles leads to the formation of a hydrogen-like system of an electron-hole pair. THz waves strongly interact with the electron-hole pair in semiconductors, because the hydrogen-like system is resonant at THz frequencies. The THz interaction can induce peculiar quantum dynamics of the electron-hole pair in semiconductor nanostructures. The resulting quantum dynamics and associated optical effects are of great interest because the fundamental physical processes have broad applications for ultrahigh-speed optoelectronic devices beyond 100 GHz. The outreach programs include optics demonstrations for K-12 students, research experience for high school students, and professional development opportunity for science and math teachers.