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Spin and charge pumping in optical superlattices

Christian Schweizer, LMU Munich

01.02.2017 at 14:00 

Topological charge pumping enables the transport of charge through an adiabatic cyclic evolution of the underlying Hamiltonian. In contrast to classical transport, the transported charge is quantized and purely determined by the topology of the pump cycle, making it robust to perturbations.
In the first part I will report on our realization of such a pump with ultracold bosonic atoms forming a Mott insulator in a dynamically controlled optical superlattice. By taking in situ images of the cloud, we observed a quantized deflection per pump cycle, and revealed the pump’s genuine quantum nature by showing a counterintuitive reversed deflection for particles in the first excited band. These results opened a route to the implementation of more complex pumping schemes, including spin degrees of freedom and higher dimensions.
Second, I will report on our experimental implementation of a spin pump with ultracold bosonic atoms in an optical superlattice. In the limit of isolated double wells, it represents a 1D dynamical version of the quantum spin Hall effect. Starting from an antiferromagnetically ordered spin chain, we periodically varied the underlying spin-dependent Hamiltonian and observed a spin current without charge transport. We demonstrated a novel detection method to measure spin currents in optical lattices via superexchange oscillations emerging after a projection onto static double wells and furthermore, directly verified spin transport through in situ measurements of the spins’ center-of-mass displacement.

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