  We experimentally demonstrate shaping of the two-photon wavefunction of
entangled photon-pairs, utilizing coherent pulse-shaping techniques. By
performing spectral-phase manipulations we tailor the two-photon wavefunction
exactly like a coherent ultrashort pulse. To observe the shaping we perform
sum-frequency generation (SFG) with an ultrahigh flux of entangled photons. At
the appropriate conditions, SFG performs as a coincidence detector with an
ultrashort response time (~100 fs), enabling a direct observation of the
two-photon wavefunction. This property also enables us to demonstrate
background-free, high-visibility two-photon interference oscillations.

Quantum Physics;Atomic Physics;Classical Physics;Optics