A quantum key generation system (100,200,300) comprising two photon detector units (110,112,210,212,310,312), two photon entanglement chains (120a,120b,220a,220b,320a,320b), and a plurality of multicore fiber links (160,260,360), wherein: each photon entanglement chain (120a,120b,220a,220b,320a,320b) extends between the two photon detector units (110,112,210,212,310,312); each photon entanglement chain (120a,120b,220a,220b,320a,320b) comprises at least one quantum repeater and first and second terminating quantum memories; the first (154a.154b,254a,254b,354a,354b) and second (156a,156b,256a,256b,356a,356b) terminating quantum memories are positioned at first and second ends of the photon entanglement chains (120a,120b,220a,220b,320a,320b), respectively; the quantum repeater (140a,140b,240a,240b,242a,242b,340a,340b) of each photon entanglement chain (120a,120b,220a,220b,320a,320b) is structurally configured to entangle a pair of photons; the plurality of multicore optical fiber links (160,260,360) are structurally configured to optically couple the quantum repeater (140a,140b,240a,240b,242a,242b,340a,340b) of each photon entanglement chain (120a,120b,220a,220b,320a,320b) to the first and second terminating quantum memories of each photon entanglement chain such that photons received by the first and the second terminating quantum memories are entangled with photons entangled by the quantum repeater(140a,140b,240a,240b,242a,242b,340a,340b); the plurality of multicore optical fiber links (160,260,360) each comprise at least two non-uniform cores (162,164) structurally configured to provide non-uniform photon propagation delay; the first (154a.154b,254a,254b,354a,354b) and second (156a,156b,256a,256b,356a,356b) terminating quantum memories of each of the two photon entanglement chains (120a,120b,220a,220b,320a,320b) form first (150,250,350) and second (152,252,352) cross-chain quantum repeaters, respectively, to generate measurable entangled particles at the cross-chain quantum repeaters (150,250,350,152,252,352); and the first and the second photon detector units (110,112,210,212,310,312) are structurally configured to receive the measurable entangled particles generated by the first (150,250,350) and second (152,252,352) cross-chain quantum repeaters (140a,140b,240a,240b,242a,242b,340a,340b), respectively. each photon entanglement chain (120a,120b,220a,220b,320a,320b) extends between the two photon detector units (110,112,210,212,310,312); each photon entanglement chain (120a,120b,220a,220b,320a,320b) comprises at least one quantum repeater and first and second terminating quantum memories; the first (154a.154b,254a,254b,354a,354b) and second (156a,156b,256a,256b,356a,356b) terminating quantum memories are positioned at first and second ends of the photon entanglement chains (120a,120b,220a,220b,320a,320b), respectively; the quantum repeater (140a,140b,240a,240b,242a,242b,340a,340b) of each photon entanglement chain (120a,120b,220a,220b,320a,320b) is structurally configured to entangle a pair of photons; the plurality of multicore optical fiber links (160,260,360) are structurally configured to optically couple the quantum repeater (140a,140b,240a,240b,242a,242b,340a,340b) of each photon entanglement chain (120a,120b,220a,220b,320a,320b) to the first and second terminating quantum memories of each photon entanglement chain such that photons received by the first and the second terminating quantum memories are entangled with photons entangled by the quantum repeater(140a,140b,240a,240b,242a,242b,340a,340b); the plurality of multicore optical fiber links (160,260,360) each comprise at least two non-uniform cores (162,164) structurally configured to provide non-uniform photon propagation delay; the first (154a.154b,254a,254b,354a,354b) and second (156a,156b,256a,256b,356a,356b) terminating quantum memories of each of the two photon entanglement chains (120a,120b,220a,220b,320a,320b) form first (150,250,350) and second (152,252,352) cross-chain quantum repeaters, respectively, to generate measurable entangled particles at the cross-chain quantum repeaters (150,250,350,152,252,352); and the first and the second photon detector units (110,112,210,212,310,312) are structurally configured to receive the measurable entangled particles generated by the first (150,250,350) and second (152,252,352) cross-chain quantum repeaters (140a,140b,240a,240b,242a,242b,340a,340b), respectively.