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Much of the research in our group is focused on quantum aspects of the
interaction of light with matter.
In some problems it is the quantum mechanical nature of matter that is
important, such as when we are trying to understand the nonlinear optical
response of semiconductors in terms of their band structures, or when we are
exploring novel "quantum interference" processes. These processes involve
the interference of two or more pathways, analogous to the interference of two
different trajectories in the familiar double-slit experiment, and can be exploited
by experimentalists to "coherently control" the effect of light on bulk materials
or nanostructures. By combining different polarizations of an incident beam, or
different incident beams, it is possible to control the number of carriers that are
injected, to inject the carriers with a large and controllable average velocity, and
to control the spins of injected carriers.
Indeed, one can even induce a "pure
spin current," in which carriers that are "spin up" are injected in one direction,
and carriers that are "spin down" in the opposite direction. Processes like this
may be of interest in applications in electronics as well as in "spintronics," the
new field of work directed towards using the spin degree of freedom of carriers
in information processing. Others are interested in their use in metrology, since
they can be used to detect and stabilize the carrier-envelope phase in a pulse of
just a few cycles. These effects are also leading to new studies in the transport
of carriers in crystals and nanostructures, and they can serve as a probe of novel
phenomena such as the spin Hall effect. New behaviour can now be explored,
and a theoretical description of much of it is still lacking.