  The Schrodinger and Heisenberg pictures are equivalent formulations of
quantum mechanics. Here we use the Schrodinger picture to calculate the
decoherence that occurs when an optical Schrodinger cat state is passed through
a beam splitter. We find that an exponentially large amount of decoherence can
occur even when there is a negligible change in the quadrature operator x(t) in
the Heisenberg picture. Similar results have been observed in the decoherence
produced by an optical amplifier, and we suggest that the usual quadrature
operators in the Heisenberg picture do not provide a complete description of
the output of optical devices.

Quantum Physics