Continuous frequency entanglement: effective finite hilbert space and entropy control
We examine the quantum structure of continuum entanglement and in the context of short-pulse down-conversion we answer the open question of how many of the uncountably many frequency modes contribute effectively to the entanglement.  We derive a set of two-photon mode functions that provide an exact, discrete, and effectively finite basis for characterizing pairwise entanglement.  Our analysis provides a basis for entropy control in two-photon pulses generated from down-conversion.