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Quantum Hall edge states with
a Bose gas
Ultracold atomic systems can be used to model condensed-matter physics,
providing precise control of system variables often not achievable in real
materials. This involves inducing charge-neutral particles to behave as if they
were charged particles in a magnetic field. To this end, PFC-supported
researchers have replicated the signature “edge state” behavior of real electrons
in the quantum Hall effect (QHE) with neutral atoms in an optical lattice.
To do so, the scientists created a Bose-Einstein condensate of a few hundred
thousand rubidium atoms and used two intersecting lasers to arrange the atoms
into a lattice pattern. A second pair of lasers, each set to a slightly different
wavelength, was trained on the lattice. Depending on the tuning of these laser
beams, the atoms were placed in one of three different quantum states
representing electrons that were either in the middle of, or at opposite edges of,
the two-dimensional lattice.
By adjusting the properties of the laser beams, the team created "artificial
magnetism", producing dynamics characteristic of real materials exhibiting the
QHE. Specifically, as would be expected of electrons, atoms in the bulk interior
of the lattice behaved like insulators. But those at the lattice edges exhibited a
distinctive "skipping" motion, producing localized edge states. The researchers
could further modify the artificial magnetic field to precisely control whether the
largest concentration of atoms was on one edge, the opposite edge, or in the
center of the lattice.
This dynamical effects are only achievable in the "high-field" limit of the artificial
field, surpassing previous work demonstrating weak artificial magnetic fields.
Working near this limit greatly expands the possibilities for engineering new
kinds of interactions relevant to condensed-matter physics.
Illustration of edge states in the optical lattice. Image
credit, Edwards/JQI
“Visualizing edge states with an atomic Bose gas in the
quantum Hall regime,” B. Stuhl, H.I. Lu, L.M. Aycock, D.
Genkina, I.B. Spielman, Science, 349, 1514 (2015)