  We apply a multichannel variable phase method to scattering from
Regge-Wheeler potentials. Using a reduced version of the WKB subtraction
developed by Candelas and Howard, this approach allows for efficient numerical
calculations of scattering data for imaginary wave number, making it possible
to compute quantum expectation values in a Schwarzschild curved spacetime
background through Wick rotation to the imaginary frequency axis. These
scattering theory techniques are also potentially applicable to a variety of
other problems involving wave propagation in curved spacetime.
