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Physics Colloquium, 17 April, 2001

Topological quantum numbers and precise measurements

David Thouless

University of Washington

In devices such as SQUIDS, Josephson voltmeters and quantum Hall bars, very precise measurements can be made with devices that are poorly characterized and depart significantly from ideal configurations. These devices make use of topological quantum numbers, which are much more robust than quantum numbers, such as angular momentum, based on symmetry. I discuss circulation in superfluids, flux in superconductors and Hall conductance in inversion layers as examples of such quantum numbers, and ask how the mathematical quantum number is related to measurable quantities. Recent work has shown analogies between the quantized Hall conductance and the Magnus force on quantized vortices. However, although corrections to quantization of the Hall conductance appear to be exponentially small, corrections to the Magnus force in superfluids can be rather large.

For more information:

  • Check out http://www.phys.washington.edu/~thouless/lisbon.ps.gz
  • or see the book Topological Quantum Numbers in Nonrelativistic Physics World Scientific, Singapore (1998).

    3.30 p.m., Smith Laboratory, Room 1005

    Refreshments served in Smith 1094 at 3:00 p.m.