Verification of EPR paradox studied by measuring spin-correlations of two protons in pair

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It is well-known that Einstein, Podolsky, and Rosen (EPR) asserted that quantum mechanics is incomplete in terms of local realism, a classical physicist's conception of nature. This is sometimes called as the EPR paradox. Bell rendered this argument quantitative and amenable to experimental verification as he showed that any local hidden variable theory will result in an inequality, which can contradict quantum mechanical predictions.We measured the spin entanglement of two protons (p-p) in the spin-singlet state [^1S_0] to test a hidden variable theory by using Bell's inequality. Results in terms of spin correlation function can be compared with predictions by the quantum mechanics as well as by the Bell's inequality. The high purity [^1S_0] state was produced by the ^1H(d, ^2He)n reaction at 270 MeV and their spin correlation was measured by the newly constructed polarimeter EPOL. Novel features of this experiment are a)use of "event-ready" detector of nearly 100% efficiency to prepa … More re an unbiased sample and b)a focal plane polarimeter of full 2π sr acceptance with a random "post-selection" of the reference axes. The result violates the Bell's inequality at a confidence level of 99.3%. This is the first-time test of the local hidden variable theories (Bell) involving strong interacting pair of massive spin 1/2 hadrons, in nearly loophole free experimental setting.We also measured for the first time the spin correlation of unlike particles, namely proton-neutron pairs in the singlet state which were produced by the ^2H(d, pn)pn reaction at 270 MeV. The proton spin-polarization was measured with EPOL and the neutron polarization was measured with newly constructed polarimeter NPOL. Data analysis is in progress.In 1989, Greenberger, Home and Zeiinger (GHZ) formulated an interesting new theorem for three-particle entanglement. To test GHZ a spin-correlation measurement for three particles is required. We have succeeded to constructed a polarimeter system for three photons for the decay of orthopositronium.In summary, this project went so smoothly and we obtained excellent results. Less