A Thouless Quantum Pump with Ultracold Bosonic Atoms in an Optical Superlattice (M. Lohse) / Direct cooling of polar molecules to submillikelvin temperatures (A. Prehn)

  • Double Feature!
  • Datum: 14.06.2016
  • Uhrzeit: 14:30 - 15:30
  • Vortragende(r): Michael Lohse, MPQ, QMBS Division / Alexander Prehn, MPQ, QD Division
  • Raum: Herbert Walther Lecture Hall
  • Gastgeber: MPQ
abstracts...

A Thouless Quantum Pump with Ultracold Bosonic Atoms in an Optical Superlattice (Michael Lohse)
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. Here, we report on the 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 observe a quantized deflection per pump cycle. We reveal the pump's genuine quantum nature by showing that, in contrast to ground state particles, a counterintuitive reversed deflection occurs for particles in the first excited band. Furthermore, we directly demonstrate that the system undergoes a controlled topological transition in higher bands when tuning the superlattice parameters. These results open the route for the implementation of more complex pumping schemes including spin degrees of freedom and higher dimensions.

Direct cooling of polar molecules to submillikelvin temperatures (Alexander Prehn)
Applications of ultracold (T<1mK) polar molecules including ultracold chemistry, quantum simulation, and high-precision spectroscopy exploit the rich internal level structure and the electric dipole moment of the molecules. The desired use of chemically diverse species requires development of direct cooling methods. However, a versatile technique to cool large numbers of molecules to the ultracold regime has been lacking.In this talk, I present direct cooling of formaldehyde (H2CO) to the microkelvin regime [1]. Our approach, optoelectrical Sisyphus cooling, which was first demonstrated with methyl fluoride (CH3F) [2], provides a simple dissipative cooling method applicable to a variety of electrically trapped dipolar molecules. By reducing the temperature by three orders of magnitude and increasing the phase-space density by a factor of 10,000 we generate an ensemble of about 300,000 trapped molecules with a temperature of about 400 µK. In addition, we control the rotational state of the molecules, resulting in a state purity higher than 80%. This record-large ensemble of ultracold, controlled molecules is an ideal starting point for further experiments, e.g., collision studies or molecular fountain experiments.
[1] A. Prehn et al., Phys. Rev. Lett. 116, 063005 (2016)
[2] M. Zeppenfeld et al., Nature 491, 570 (2012).

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