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Physics and Astronomy

Physics & Astronomy Colloquium

3:30 PM, Friday, October 16, 2009
Room 155, Chem-Phys Building

Dr. Alex Seidel
Department of Physics
Washington University, St. Louis

"The bare essentials of topological orders in fractional quantum Hall liquids''

Condensed matter physicists are generally faced with the task of solving problems involving some 1024 particles that interact strongly. Amazingly, in many cases this task of seemingly hopeless complexity is amenable to the following simple strategy: Try to find a way to (almost) switch off the interactions in a manner that preserves all the fundamental properties of the system. If this is possible, one says that the system is ``adiabatically connected'' to a non-interacting system.

In the past 20+ years, however, much focus has been on problems where the traditional approach does not seem feasible. In particular, a new paradigm has surfaced which applies to certain novel incompressible quantum liquids that are said to have ``topological order''. This new paradigm encompasses the fractional quantum Hall liquids, and possibly states that can be realized in quantum magnets.

The phenomenology of topologically ordered states is very exotic, including fractionally charged excitations and anyonic braiding statistics. This fact seems to preclude the possibility that these states have simple non-interacting limits. In spite of this, it will be shown in this talk that such a trivial limit does exist for fractional quantum Hall liquids. In this limit, a simple language of one-dimensional patterns emerges. I will show how this language efficiently encodes the defining quantum numbers of the underlying quantum Hall state, such as fractional charges, characteristic degeneracies, and even non-abelian braiding statistics.

Refreshments will be served in CP 179 at 3:15 PM