Sum-frequency generation with broadband entangled photons

Full text: We experimentally demonstrate sum-frequency generation (SFG) with entangled photon-pairs, generating as many as 40,000 SFG photons per second, visible even to the naked eye. The key element in our scheme is the generation of an ultrahigh flux of broadband entangled photons, while maintaining their nonclassical properties. This is made possible by keeping the down-converted spectrum as broadband as possible, orders of magnitude wider than the pump. The nonclassical nature of the interaction is exhibited by a linear intensity-dependence of the process. We then demonstrate shaping of the two-photon wavefunction, utilizing coherent pulse-shaping techniques. By performing spectral-phase manipulations we tailor the twophoton wavefunction exactly like a coherent ultrashort pulse. For this we exploit the SFG process as an ultrafast (∼ 100 fs) coincidence detector, such as electronically unattainable, to directly observe the twophoton wavefunction. (author)