  We predict that all-optically reconfigurable generation of photon pairs with
tailored spatial entanglement can be realized via spontaneous parametric
down-conversion in integrated nonlinear coupled waveguides. The required
elements of the output quantum wavefunction are directly mapped from the
amplitudes and phases of the classical laser pump inputs in each waveguide.
This is achieved through special nonuniform domain poling, which locally
inverts the sign of quadratic nonlinear susceptibility and accordingly shapes
the interference of biphoton quantum states generated along the waveguides. We
demonstrate a device configuration for the generation of any linear combination
of two-photon Bell states.
