Quantum key distribution (QKD) provides information-theoretic security based on the laws of quantum mechanics. The desire to reduce costs and increase robustness in real-world applications has motivated the study of coexistence between QKD and intense classical data traffic in a single fiber. Previous works on coexistence in metropolitan areas have used wavelength-division multiplexing, however, coexistence in backbone fiber networks remains a great experimental challenge, as Tbps data of up to 20 dBm optical power is transferred, and much more noise is generated for QKD. Here we present for the first time, to the best of our knowledge, the integration of QKD with a commercial backbone network of 3.6 Tbps classical data at 21 dBm launch power over 66 km fiber. With 20 GHz pass-band filtering and large effective core area fibers, real-time secure key rates can reach 4.5 kbps and 5.1 kbps for co-propagation and counter-propagation at the maximum launch power, respectively. This demonstrates feasibility and represents an important step towards building a quantum network that coexists with the current backbone fiber infrastructure of classical communications.

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The liquid entrainment in Higee devices exists and reduces separation efficiency. The flooding in Higee devices, called Higee flooding, sets an upper limit of the allowable throughputs, and the different flooding criteria were proposed by researchers. Using air-water system, the experiments of liquid entrainment and Higee flooding were carried out in a rotating zigzag bed(RZB), as a new Higee device. The RZB rotor had an inner diameter of 0.101m, outer diameter of 0.284m and height of 0.051m. The distillation experiment was conducted in the same RZB to investigate the effect of the liquid entrainment on the separation efficiency. The results show that the liquid entrainment in RZB contains liquid-droplet and liquid-film entrainment. The liquid-film entrainment is far higher than the liquid-droplet entrainment. And the excessive liquid-film entrainment at the outer edge of RZB rotor severely lowered separation efficiency. The point, at which the pressure drop increases sharply with increasing superficial liquid velocity, was first to be taken as a new Higee flooding criterion. The new Higee flooding criterion reflected the real flooding in RZB, and the previous criteria could not reflect. The new Higee flooding criterion can also applied in rotating packed beds.

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