Archimedes screw.
Continuous rotation of the screw pumps water from the lower-lying
reservoir into the upper one. MPQ, Quantum
Many-Body Systems Division
(December 17, 2015) Scientists
from Munich realize a dynamic version of the quantum Hall effect in optical superlattices
The transport of particles is usually induced by applying an
external gradient to a system. Water, for example, flows down a slope and
electric current is generated by applying a voltage. But already in ancient
times another way of generating a directional motion was known: by periodic
modulation of a system, as can be seen in the famous Archimedes' screw. More than
30 years ago, the Scottish physicist David Thouless predicted that a similar
phenomenon should also occur in quantum mechanical systems, so called
topological pumping. A group of researchers from the
Ludwig-Maximilians-Universität München and the Max Planck Institute of Quantum
Optics, led by Professor Immanuel Bloch and in collaboration with the
theoretical physicist Oded Zilberberg (ETH Zürich), have now successfully
implemented such a topological charge pump with ultracold atoms in an optical
lattice for the first time.
In 1983, inspired by the recently discovered two-dimensional
quantum Hall effect, for which Klaus von Klitzing was awarded the Nobel prize
in physics in 1985, Thouless came up with the idea that a similar phenomenon
could also be observed in one-dimensional systems if their parameters are
varied periodically. This dynamic version of the quantum Hall effect enables
transport of particles without an external bias. Due to its special, so called
topological properties, this transport occurs in a quantized fashion so that the
particles move exactly by a well-defined distance per cycle. In addition, the
transport is extremely robust with respect to external perturbations and is not
affected by small changes of the system. This is of particular interest from a
technological point of view since it could facilitate a more precise definition
of the standard for electrical current. Despite long lasting efforts, however,
the realization of such a quantized charge pump has remained out of reach up to
now.
Implementation of
a topological charge pump in an optical superlattice.(a) An optical
superlattice
is created by ... [more] MPQ, Quantum
Many-Body Systems Division
Ultracold atoms in optical lattices constitute an almost
ideal model system for such experiments since they can be controlled and
detected very well. Inside a vacuum, the atoms can be cooled to a temperature
close to absolute zero and subsequently be transferred into a periodic
potential that is created by the interference of multiple laser beams. A
superlattice is a special kind of these optical lattices that is created by
superimposing two standing waves of light with different periodicities. In the
experiment in Munich, the periods of the lattices where chosen in such a way
that they differ by a factor of two. This gives rise to double well potentials
as shown in Fig. 2.