  The photon-pairs generated through spontaneous parametric down-conversion
(SPDC) possess strong correlations in their transverse position and momentum
degrees of freedom. For such photon pairs, the transverse position correlation
length depends on the crystal thickness and the pump wavelength, whereas the
transverse momentum correlation length depends on the beam waist and spatial
coherence length of the pump. By controlling these parameters, it is possible
to engineer the spatial entanglement. Here, we utilize the circular asymmetry
of the pump by using an elliptical-Gaussian beam to change the degree of
entanglement in transverse directions, which we call anisotropic entanglement.
We show the interrelation between the degree of anisotropic entanglement and
the asymmetry in the beam width. In addition, we also show that for a highly
asymmetric pump beam, the entanglement along the y-direction completely
vanishes, whereas the entanglement in the x-direction remains intact.
