Research

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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 complicated system.