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Characterization of coincident-frequency entangled source in quantum synchronization application

The frequency entangled photon pairs generated via spontaneous parametric down-conversion process (SPDC) have been found the main resources in quantum clock synchronization protocols. The spectral indistinguishibility of the photon pairs is a key factor for the achievement of quantum clock synchronization. In this paper, we characterize both theoretically and experimentally the factors degrading the spectral indistinguishibility of the generated coincident-frequency entangled photon pairs under extended phase matching conditions. The results show that due to the nonnegligible second-order dispersion contribution to the phase mismatching, the broadening of the pulse pump bandwidth and the lengthening of the nonlinear crystal all lead to the degradation.