Coherent control: Theory

Since the inception of quantum mechanics almost a century ago, a prime activity has been the observation of quantum phenomena in virtually all areas of chemistry and physics. However, the natural evolution of science leads to the desire to go beyond passive observation to active manipulation of quantum mechanical processes. Achieving control over quantum phenomena could be viewed as engineering at the atomic scale guided by the principles of quantum mechanics, for the alteration of system properties or dynamic behavior. From this perspective, the construction of quantum mechanically operating solid-state devices through selective material growth would fall into this category. The focus of this article is principally on the manipulation of quantum phenomena through tailored laser pulses. The suggestion of using coherent radiation for the active alteration of microworld processes may be traced to the early 1960s, almost immediately after the discovery of lasers. Since then, the subject has grown enormously to encompass the manipulation of (1) chemical reactions, (2) quantum electron transport in semiconductors, (3) excitons in solids, (4) quantum information systems, (5) atom lasers, and (6) high harmonic generation, amongst other topics. Perhaps the most significant use of these techniques may be their provision of refined tools to ultimately better understand the basic physical interactions operative at the atomic scale. Regardless of the particular application of laser control over quantum phenomena, there is one basic operating principle involved: active manipulation of constructive and destructive quantum wave interferences. This process is depicted in Fig. 1, showing the evolution of....