  The concept of correlated two-photon spiral imaging is introduced. We begin
by analyzing the joint orbital angular momentum (OAM) spectrum of correlated
photon pairs. The mutual information carried by the photon pairs is evaluated,
and it is shown that when an object is placed in one of the beam paths the
value of the mutual information is strongly dependent on object shape and is
closely related to the degree of rotational symmetry present. After analyzing
the effect of the object on the OAM correlations, the method of correlated
spiral imaging is described. We first present a version using parametric
downconversion, in which entangled pairs of photons with opposite OAM values
are produced, placing an object in the path of one beam. We then present a
classical (correlated, but non-entangled) version. The relative problems and
benefits of the classical versus entangled configurations are discussed. The
prospect is raised of carrying out compressive imaging via twophoton OAM
detection to reconstruct sparse objects with few measurements.
