PROBLEM TO BE SOLVED: To provide a quantum-entangled light source which can create an entangled photon pair having a narrow spectrum line width in a communication wavelength band.;SOLUTION: A light source having a quantum tangle for long-distance quantum communication is a quantum-entangled light source which is used in quantum communication comprises nonlinear crystals and a resonator. The nonlinear crystals create a photon pair having a wavelength corresponding to an attenuation characteristic of a transmission path of the quantum communication. The resonator makes the entangled photon pair circle by a number not smaller than a prescribed average circling number, and emits the circled entangled photon pair.;SELECTED DRAWING: Figure 2;COPYRIGHT: (C)2019,JPO&INPIT
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