Protecting quantum superpositions from the outside world
Alexander I. Lvovsky · Physics · 2009
Invariant entangled states remain unchanged under simultaneous identical unitary transformations of all their subsystems.We experimentally generate and characterize such invariant two-, four-, and six-photon polarization entangled states.This is done only with a suitable filtering procedure of multiple emissions of entangled photon pairs from a single source without any interferometric overlaps.We get the desired states utilizing bosonic emission enhancement due to indistinguishability.The setup is very stable and gives high interference contrasts.Thus, the process is a very likely candidate for various photonic demonstrations of quantum information protocols.