  In the past two decades, quantum key distribution networks based on telecom
fibers have been implemented on metropolitan and intercity scales. One of the
bottlenecks lies in the exponential decay of the key rate with respect to the
transmission distance. Recently proposed schemes mainly focus on achieving
longer distances by creating a long-arm single-photon interferometer over two
communication parties. Despite their advantageous performance over long
communication distances, the requirement of phase-locking between two
independent lasers is technically challenging. By adopting the
recently-proposed mode-pairing idea, we realize high-performance quantum key
distribution without global phase-locking. Using two independent off-the-shelf
lasers, we show a quadratic key-rate improvement over the conventional
measurement-device-independent schemes in the regime of metropolitan and
intercity distances. For longer distances, we also boost the key rate
performance by three orders of magnitude via 304 km commercial fiber and 407 km
ultra-low-loss fiber. We expect this ready-to-implement high-performance scheme
to be widely used in future intercity quantum communication networks.
