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In other work it is the quantum mechanical nature of light that is important.
Nonlinear processes have been used for years to create nonclassical states of
light, such as pairs of "entangled photons." We are looking at the possibility
of using artificially structured materials, such as ring resonators, to enhance
the production of these entangled photons and to control the properties of the
bi-photon wave function generated.
Such nonclassical states of light play an
important part in developments in quantum information processing, and the
theory of the generation and manipulation of nonclassical optical states in novel
structures is just being developed.
At a fundamental theoretical level the effort
is exciting because different experimental scenarios are described by different
nonlinear quantum field theories, and these can actually be studied in detail in
the laboratory by our experimental colleagues.
In many of these problems the subject of "decoherence" plays a crucial role.
Very roughly speaking, it describes how a quantum system not completely isolated
from its environment tends to acquire a classical nature. Decoherence
and attempts to eliminate it play a central role in studies of possible quantum
computing scenarios, of course. Our focus is more on how to understand and
describe different types of decoherence, such as that which appears in a manybody
system where the kind of few-particle operators one normally studies suffer
a kind of "decoherence" due to each particle interacting with the others. Here
there is no simple separation of "system" and "environment," but rather an
emergence of a classical-like nature in the behaviour of certain aspects of a very