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lead further to new discoveries: the authors succeeded in producing the world’s rst generation of a high-dimension-al entangled photon pair, which is characterized by more than 10 degrees of freedom, and the photon pair’s quantum entanglement is distributed in more than ten dierent frequencies[8]. To evaluate the validity of these experimen-tal results, we constructed a theoretical framework that enables accurate modeling of optical experiments in quantum entanglement research, without the need to resort to large-scale numerical simulations[9][10].e research described in this report is still in the basic stage, and does not at present indicate a direct link to the upgrading of the performance of telecommunication. However, the combination of this new knowledge in physical science is expected to help accelerate the establish-ment of underlying technologies for future quantum node applications.4Integration of quantum entanglement sourceTo make the quantum entanglement source a more practical device, a higher degree of integration is necessary using versatile materials as far as possible. We are also tackling the integration of a quantum entanglement source that operates in telecom wavelengths, attempting to put silicon photonics to use. Figure 4(a), (b) shows an example: an integrated circuit consisting of a tiny silicon ring resona-tor (approx. 10 μm radius) and two silicon waveguides anking the resonator is constructed on a board, and a four-wave-mixing process (a non-linear optical process) is initiated within the ring resonator by introducing excita-tion light via the waveguide to generate quantum entangled photon pairs. By introducing a 1551.63 nm pump laser, the generation of a correlated photon pair was observed at two wavelengths, 1539.01 and 1564.43 nm, both falling in the range of telecom wavelengths[11]. From the output, photon pairs with time-bin entanglement—entanglement in terms of positional information along the time axis—can be generated by passing each output photon pair through an asymmetric interferometer (planer light wave circuit: PLC).e entanglement thus generated showed a high degree of quantum visibility (≧90%), proving it to be a high purity quantum entanglement (Fig.4(c)). We also suc-ceeded in generating “wavelength-multiplexed quantum entangled photon pairs” (simultaneous generation of two photon pairs from four wavelengths) through careful FiF2　Steps for swapping quantum entanglementEntanglement swapping protocolAABCC{Entangled photon pairTwo-photon measurement on entangled basisEntanglement between A and CEntangled photon pairFiF3　Entanglement swapping experiment Left: Overview of experimental setup Upper right: Photograph Lower right: Experimental results09018027036002004006008001000Visibility90.6% (78.0%)65.7% (56.1%)87.4% (74.6%)63.6% (54.4%)Angle of polarizer A(deg)Four-photon coincidence counts during a period of 30 secondsAngle of polarizer C(deg)045901354 Quantum Node Technology52　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 1 (2017)