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!
- Date: Jun 14, 2016
- Time: 02:30 PM - 03:30 PM (Local Time Germany)
- Speaker: Michael Lohse, MPQ, QMBS Division / Alexander Prehn, MPQ, QD Division
- Room: Herbert Walther Lecture Hall
- Host: MPQ
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).