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A Quantum Kicked Top with Cold Atomic Spins

Souma Chaudhury, University of Arizona

(Session 4 : Friday from 17:30-18:00)

Abstract. Complexity in classical as well as quantum physics arises through the coupling of multiple degrees of freedom. Recent theoretical studies have shown a connection between the dynamical rate of entanglement generation in a bipartite quantum system and the presence of chaos in the corresponding classical dynamics. In order to explore this and similar questions that lie at the boundary between quantum information science and quantum chaos we have developed a version of the quantum kicked top based on laser cooled atomic spins driven by a pulsed magnetic field and a rank 2 tensor light shift. Among the advantages offered by our system are the ability to prepare arbitrary initial spin states, the ability to precisely implement the desired non-linear dynamics, and the ability to accurately measure the entire spin density matrix and thus obtain accurate snapshots of the evolving quantum state.

We will present results from an experiment that implemented a quantum kicked top for the F=3 hyperfine ground state of Cs. Initial spin states were chosen to overlap with regular or chaotic areas of the classical phase space map, and the resulting spin Husimi distribution measured after each step in a series of 50 kicks. The spin dynamics seen in the experiment agrees closely with the predictions of theory, including dynamical tunneling between regular islands, rapid spreading of states throughout the chaotic sea, and surprisingly robust signatures of classical phase space structures even after many kicks and significant decoherence. As expected, the entanglement generated between electronic and nuclear spin is larger when the corresponding classical dynamics is chaotic, though the difference "while clear" is modest due to the small size of the total spin. Future versions of the experiment may circumvent this limitation by driving the electronic and nuclear spins independently, or by working with the collective spin of an ensemble of atoms.