Multi-Photon Quantum Cryptography And Quantum Cloning

Entangled photons play an important part in quantum optics when exploring the nature of nonlocal quantum correlations. They represent a powerful resource for quantum information experiments, including teleportation and cryptography. In the regime of spontaneous parametric downconversion entangled pair production is still quite inefficient. However, this group has used stimulated parametric downconversion to produce photon states entangled both in polarization and photon number. By this technique, the group has significantly increased the probability amplitudes of entangled pairs and entangled states of higher photon number, which make possible new kinds of efficient cryptography protocols and stronger violation of 'locality' through Bell-type measurements. We show in addition, that this entangled photon source can perform effective universal quantum cloning of single photons.