Qubitrium team reports 548/1550 nm photon-pair source to cut QKD detector costs
Researchers at Qubitrium B.V. (Delft, Netherlands) and Qubitrium A.S. (Istanbul, Türkiye) describe a nondegenerate photon-pair source using two ppKTP crystals pumped at 405 nm, emitting pairs at 548 and 1550 nm, in an arXiv preprint that is not yet peer reviewed. The unoptimized module produces about 1.53 MHz of pairs per milliwatt of pump power, which the authors say is 2.7 times a comparable published source (0.56 MHz/mW), and it collects 13% of pairs on the 548 nm arm and 23% on the 1550 nm arm. In an asymptotic BBM92 model of a 50 km link, the current module with one superconducting nanowire detector costs about $376 per secret Gbit over two years, versus $301 for a generic one-detector link and $66 for a generic two-detector link. With target improvements of 52% collection and double the brightness, the authors model the cost at 40% of a two-detector link. The current module produces polarization-correlated, not entangled, pairs, and the cost advantage depends on demonstrating entanglement in a future version.