Photon-photon polarization correlations as a tool for studying parity   non-conservation in heliumlike Uranium
  Due to electron-nucleus weak interaction, atomic bound states with different parities turn out to be mixed. We discuss a prospect for measuring the mixing parameter between the nearly degenerate metastable states 1s_{1/2} 2s_{1/2} : J = 0 and 1s_{1/2} 2p_{1/2} : J = 0 in heliumlike Uranium. Our analysis is based on the polarization properties of the photons emitted in the two-photon decays of such states. 
Filippo Fratini, Sergiy Trotsenko, Stanislav Tashenov, Thomas   Stoehlker, Andrey Surzhykov
physics.atom-ph quant-ph