Nonlinear Dynamics in Quantum Wells at Terahertz Frequencies

点击翻译按钮获取中文摘要

w:\awards\awards96\*.doc 9623874 Sherwin This project will explore non-equilibrium and non linear properties of quantum wells at Terahertz frequencies. The objective is to observe intrinsic optical bistability, period- doubling, chaos and Rabi oscillations in wide quantum well structures. These effects have recently been predicted by computer simulations using the Hartree approximation which have modeled quantum wells containing many electrons and which are subject to intense Terahertz radiation. The experiments will be performed using the UC Santa Barbara Free-Electron Laser. Semiconductor structures which are specially tailored for the quantum chaos experiments will be grown and characterized in collaboration with collaborators at UC Santa Barbara. %%% In recent years, many investigators have been struggling to reconcile quantum mechanics with the existence of chaos in Newtonian dynamics. The field is called 'quantum chaos'. The traditional approach to 'quantum chaos' is to study the quantum mechanics of systems whose classical dynamics are chaotic. This project takes a somewhat different approach and focuses on a search for a purely quantum mechanical version of chaotic motion. That is, motion that is chaotic, but has no analogue in classical mechanics. The system to be studied are electrons confined in thin layers of semiconductor quantum wells, and which are driven by extremely strong fields which oscillate several trillion times each second. Simulations indicate that such systems can exhibit a chaotic motion with no classical analogue. The strong fields are generated by UC Santa Barbara's unique Free-Electron Laser. The project will initially seek to observe precursors of chaos, called bifurcations, in which a small change in a parameter (for example, the strength of the oscillating field) causes a dramatic change in the character of motion. A bifurcation of immediate interest is so-called "period-doubling", in which the system's oscillations occur at twice the period of oscillations in the driving field. Having found such bifurcations, the project will then seek chaotic motion in a quantum system. ***