Entanglement test on a microscopic-macroscopic system

Phys Rev Lett. 2008 Jun 27;100(25):253601. doi: 10.1103/PhysRevLett.100.253601. Epub 2008 Jun 26.

Abstract

A macrostate consisting of N approximately 3.5x10{4} photons in a quantum superposition and entangled with a far apart single-photon state (microstate) is generated. Precisely, an entangled photon pair is created by a nonlinear optical process; then one photon of the pair is injected into an optical parametric amplifier operating for any input polarization state, i.e., into a phase-covariant cloning machine. Such transformation establishes a connection between the single photon and the multiparticle fields. We then demonstrate the nonseparability of the bipartite system by adopting a local filtering technique within a positive operator valued measurement.