The spin and the twist, and other tales of quantum control
The spin degrees of freedom of a cold atom ensemble provide an attractive testing ground for new ideas in quantum control and measurement, with potential applications ranging from quantum information processing to quantum metrology. I will briefly review the use of tensor AC Stark shifts to achieve universal control of hyperfine spins of arbitrary magnitude , and then focus on an experiment in which we used the resulting toolbox to realize a common paradigm for quantum chaos - the quantum kicked top - and observe its behavior directly in quantum phase space. This system is based on the combined electronic and nuclear spin of a single Cs atom and is therefore deep in the quantum regime. We nevertheless have found good correspondence between the quantum dynamics and classical phase space structures, and obtained the first experimental evidence for dynamical entanglement as a signature of chaos . We are now exploring a new approach based entirely on DC, radio frequency and microwave magnetic fields, which eliminates the problem of photon scattering and provides universal control over the entire atomic ground manifold . The longer coherence times available with the new approach will allow us to explore ideas related to robust control and constructive design of unitary transformations.
 I. H. Deutsch and P. S. Jessen, Opt. Comm. 283, 681 (2010).
 S. Chaudhury et al., Nature 461, 768 (2009).
 S. T. Merkel et al., Phys. Rev. A 78, 023404 (2008).
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