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Twin-field (TF) quantum key distribution (QKD) has rapidly risen as the most viable solution to long-distance secure fibre communication thanks to its fundamentally repeater-like rate-loss scaling. However, its implementation complexity, if not successfully addressed, could impede or even prevent its advance into real-world. To satisfy its requirement for twin-field coherence, all present setups adopted essentially a gigantic, resource-inefficient interferometer structure that lacks scalability that mature QKD systems provide with simplex quantum links. Here we introduce a novel technique that can stabilise an open channel without using a closed interferometer and has general applicability to phase-sensitive quantum communications. Using locally generated frequency combs to establish mutual coherence, we develop a simple and versatile TF-QKD setup that does not need service fibre and can operate over links of 100 km asymmetry. We confirm the setup's repeater-like behaviour and obtain a finite-size rate of 0.32 bit/s at a distance of 615.6 km., Comment: 14 pages, 7 figures

Additional file 1: Table S1. Comparison of d-xylonic acid production by different organisms. Table S2. Strains, plasmids and primers used in this study. Figure S1. Comparison of d-xylonic acid production by different G. oxydans strains. The conversions were carried out in shake flasks at 30 ��C and 200 rpm. The reaction system contained 40 g/L d-xylose, 50 mM citric acid buffer (pH 5.8) and 1.90 gdcw/L resting cells. Figure S2. The activities of mGDHs from G. oxydans DSM2003 and G. oxydans/pBBR-R3510-mGDH toward xylose. Figure S3. Batch D-xylonic acid production from 535 g/L d-xylose by G. oxydans/pBBR-R3510-mGDH. The conversion was carried out in a 7 L fermenter with 4 vvm aeration, 30 ��C and 600 rpm conditions. The pH was maintained at 5.8 by using a 4 M NaOH solution. The reaction system contained 535 g/L d-xylose and 3.82 gdcw/L resting cells. Figure S4. Transformation of furfural and HMF by G. oxydans/pBBR-R3510-mGDH and G. oxydans DSM2003, respectively. (a) Transformation of furfural; (b) transformation of HMF. The conversions were carried out in shake flasks at 30 ��C and 200 rpm. The reaction system contained 0.5 or 2.5 g/L furfural (HMF), 40 g/L d-xylose, 50 mM citric acid buffer (pH 5.8), and 1.90 gdcw/L resting cells. Figure S5. The activities of the membrane-bound dehydrogenases of membrane fractions from G. oxydans DSM2003 and G. oxydans/pBBR-R3510-mGDH toward furfural and HMF.