title: Interferometers and decoherence matrices
abstract: It is shown that the Lorentz group is the natural language for two-beam interferometers if there are no decoherence effects. This aspect of the interferometer can be translated into six-parameter representations of the Lorentz group, as in the case of polarization optics where there are two orthogonal components of one light beam. It is shown that there are groups of transformations which leave the coherency or density matrix invariant, and this symmetry property is formulated within the framework of Wigner's little groups. An additional mathematical apparatus is needed for the transition from a pure state to an impure state. Decoherence matrices are constructed for this process, and their properties are studied in detail. Experimental tests of this symmetry property are possible.
authors.affiliation: National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. han@trmm.gsfc.nasa.gov
authors.initials: D
authors.lastname: Han
authors.initials: YS
authors.lastname: Kim
authors.initials: ME
authors.lastname: Noz