Ultracold Bosonic Atoms in Optical Superlattices
Ultracold atoms in optical lattices are a promising model system for studying quantum many-body systems. The charge neutrality of atoms, however, prevents a direct simulation of the effects of magnetic fields on charged particles like for example the quantum Hall effect.
In the first part of my PhD, we have been working on the experimental implementation of a technique that allows for the generation of large homogeneous and tunable artificial magnetic fields in optical lattices, i.e. makes the neutral atoms behave as if they were charged particles in an external magnetic field. It is based on laser-assisted tunneling which can be used to engineer position-dependent complex tunneling amplitudes such that atoms moving in the lattice accumulate a phase shift equivalent to the Aharonov-Bohm phase for charged particles in magnetic fields.
Using this technique and in collaboration with B. Paredes (Madrid), we could observe cyclotron orbits of individual atoms  as well as an analogon of the Meissner effect for atoms in quasi-1D ladder systems . Moreover, together with S. Nascimbène (Paris), N. Cooper (Cambridge) and N. Goldman (Brussels), we could demonstrate the non-trivial topological properties of the band structure in the presence of an artificial magnetic field by measuring the Chern number of lowest band in the Hofstadter model .
In the past year, we have been studying so-called topological charge pumps that enable the transport of charge through an adiabatic cyclic evolution of the Hamiltonian even in insulating systems. For filled bands, this motion is quantized and extremely robust against perturbations as the transported charge is related to a topological invariant. It can therefore be regarded as a dynamical version of the integer quantum Hall effect. In a joint project with O. Zilberberg (Zurich), we could realize such a pump with bosonic atoms in a dynamically controlled optical superlattice and observe the quantized deflection for the first time .
 M. Aidelsburger, M. Atala, M. Lohse, J.T. Barreiro, B. Paredes, and I. Bloch, “Realization of the Hofstadter Hamiltonian with Ultracold Atoms in Optical Lattices”, Phys. Rev. Lett. 111, 185301 (2013)
 M. Atala, M. Aidelsburger, M. Lohse, J.T. Barreiro, B. Paredes and I. Bloch, “Observation of chiral currents with ultracold atoms in bosonic ladders”, Nature Physics 10, 588 (2014)
 M. Aidelsburger, M. Lohse, C. Schweizer, M. Atala, J.T. Barreiro, S. Nascimbène, N.R. Cooper, I. Bloch and N. Goldman, “Measuring the Chern number of Hofstadter bands with ultracold bosonic atoms”, Nature Physics 11, 162 (2015)
 M. Lohse, C. Schweizer, O. Zilberberg, M. Aidelsburger and I. Bloch, “A Thouless quantum pump with ultracold bosonic atoms in an optical superlattice“, Nature Physics 12, 350 (2016)
 C. Schweizer, M. Lohse, R. Citro and I. Bloch, “Spin Pumping and Measurement of Spin Currents in Optical Superlattices“, Phys. Rev. Lett. 117, 170405 (2016)
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