Coherence control of spin and charge currents

Recently scientists have made considerable progress in using optical phase to control physical, chemical and biological processes. In a collaboration between the University of Toronto and the University of Iowa, we have shown how optical phase can be used to control electron density and currents as well as spin density and spin currents in bulk (3-D) or quantum well (2-D) semiconductors as well as carbon nanotube (1-D) systems [1-3]. This type of control is based on quantum interference in optical absorption pathways, such as that associated with single and two-photon absorption of a two color beam, or between pathways associated with orthogonal polarization states associated with a single color beam. We review our most recent results, showing in particular, how emitted THz radiation can be used as a diagnostic of ultrafast transient charge currents, and how the ability to generate and control spin currents permits observation of a spin Hall effect for ballistic carriers.