FISHER2	Switching magnetism with light: controlling the spin state of rare-earth atoms in solid-state traps
Type	Theoretical
#students	1
Orientation	Why is the scientific problem of interest at all? Magnetism – the interaction between electron spins in solids – is a fascinating and intrinsically quantum phenomenon, and one that has applications from classical data storage to quantum information processing. Yet frequently we have very little control over the magnetic interactions at the atomic scale. This project will explore a way of attaining that control, using light.
How	How is the research going to shed light on the given problem?. The magnetism of rare earth compounds (in which one or more of the elements has a partially filled f-shell) is determined by the relative alignment of the spin and orbital angular momentum of the f-electrons. Thanks to a detailed spectroscopic study we now know the Hamiltonian and interactions of the electrons on the Ho^3+ ion of the ionic compound LiHoF4. We know that particular excitations can turn the magnetism on and off by changing the alignment.
What	What is the specific thing that the student will do, and how does it fit inside the overall project? Using an existing model of the electrons and in close collaboration with experiments, the student will calculate the laser pulse characteristics necessary to control the spin of the Ho3+ ions, and will participate in the formulation and interpretation of experiments to test whether this is possible. If the answer is ‘yes’ it will be a significant ‘first’ in the optical control of magnetic phenomena.
Special Knowlegde	A good knowledge of, and interest in, quantum mechanics would be a significant advantage.
Supervisor	Prof. Andrew Fisher andrew.fisher@ucl.ac.uk Dr Guy Matmon