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Charge delocalisation and hopping in an ultra-cold atomic lattice

Final Activity Report Summary - COLD RYDBERG LATTICE (Charge delocalisation and hopping in an ultra-cold atomic lattice)

Using lasers, a cloud of atoms can be cooled to within a millionth of a degree above absolute zero. Atoms that are this cold hardly move at all, and they can be trapped using laser beams to make a crystal of regularly spaced atoms held in place by light, known as an optical lattice. The aim of this project is to study what happens when we excite the electrons in these atoms to high energies using a pulse of laser light. Normally the electrons in an atom orbit close to the nucleus, but if we give the outermost electron more and more energy, its orbit gets larger and larger. Eventually the electron orbits of neighbouring atoms in the lattice begin to overlap, and the electrons no longer belong to a particular atom and can spread out along the lattice. This concept is important in many areas of physics, for example in explaining how the electrons in a metal free themselves to form an electrical current. The advantage of studying this with ultra-cold atoms trapped in an optical lattice is that the properties of each of the atoms in the lattice can be controlled extremely precisely.

This objective of this five-year long project is to study how charge is transported in these ultra-cold gases, and to see if we can control it at the level of a single atom. During the first year of the project, as funded by this proposal, we made important progress towards our goal. The scientific highlight of our work so far was the observation of highly excited states in a beam of strontium atoms using a new, non-destructive technique based on measuring the absorption of beam of laser light. This new development will be a useful tool for measuring the energies of the atoms in our ultra-cold, highly excited samples.