  Spatial modes of light directly give the most easily accessible degree of
freedom that span an infinite dimensional Hilbert space. The higher dimensional
spatial mode entanglement realized using spontaneous parametric down conversion
(SPDC) process is generally restricted to the subspace defined by a single
spatial mode in pump. Access to other modal subspaces can be realized by
pumping beams carrying several easily tunable transverse modes. As a
proof-to-principle experiment, we generate twin-photon states in a nonlinear
SPDC process with pump as a superposition of first order Laguerre-Gaussian (or
Hermite-Gaussian) modes. We show that the generated states can be easily tuned
between different subspaces by controlling the respective modal content in the
pump superposition.
