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We observed high-purity correlated and entangled photon pairs generated through spontaneous four-wave mixing (SFWM) in a silicon wire waveguide (SWW). Employing a nano-scale silicon waveguide with a low loss mode size converter, we obtained a high coincidence to accidental coincidence ratio (CAR) of around 200 that was larger than that of cooled dispersion shifted fiber (DSF) by a factor 3.2, and observed the two-photon interference fringe of time-bin entangled photons with > 95% visibility without subtracting the accidental coincidences.

The direct 3α decay branch from the 02+ state at Ex=7.65  MeV in 12C, which is known as the Hoyle state, is considered to affect the triple-α reaction rate strongly and to give crucial information on its structure. We have performed a high-precision measurement of the 3α decay from this state using the 12C(12C,3α)12C reaction at E12C=110  MeV. The branching ratio of the direct 3α decay was under the detection limit in the present experiment. By comparing with Monte Carlo simulations for three decay mechanisms as the sequential decay through the ground state of ^{8}Be, the direct decay with equal energies of three α particles, and the direct decay to the phase space uniformly, we have obtained the upper limit of 0.2% on the direct 3α decay.

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