Coherence in low-energy excitations of magnetic systems

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The effects of quantum physics normally show up only in very small things (such as atoms or molecules). Recently, however, quantum behaviour has shown up in macrosocpic objects, such as magnetic materials. If one takes such a material and subjects it to the magnetic field from an alternating current, one finds that the way it responds is dominated by well-defined excitations that ring quantum-mechanically for surprisingly long times. These new excitations are a little like new particles, emerging from the complex and disordered state of the magnet.Why does this happen? At present, nobody knows. The reason is that we have no theory that can describe precisely which aspescts of a system continue to behave quantum-mechanically as its size is increased. The aim of this project is to provide such a theory, by generalising previous approaches which look at the way other measurable quantities (such as the degree of coordination among the magnetic atoms) change as we look on longer and longer length-scales.Why is this interesting? If these long-lived quantum-mechanical excitations can be properly understood, we will have access to new quantum-mechanical objects with which we can not only test fundamental theories, but which can also act as building blocks for technology. For example, they might be used to represent or process information in new ways.