  Twin-field quantum key distribution (TF-QKD) has emerged as a promising
solution for practical quantum communication over long-haul fiber. However,
previous demonstrations on TF-QKD require the phase locking technique to
coherently control the twin light fields, inevitably complicating the system
with extra fiber channels and peripheral hardware. Here we propose and
demonstrate an approach to recover the single-photon interference pattern and
realize TF-QKD \emph{without} phase locking. Our approach separates the
communication time into reference frames and quantum frames, where the
reference frames serve as a flexible scheme for establishing the global phase
reference. To do so, we develop a tailored algorithm based on fast Fourier
transform to efficiently reconcile the phase reference via data
post-processing. We demonstrate no-phase-locking TF-QKD from short to long
distances over standard optical fibers. At 50-km standard fiber, we produce a
high secret key rate (SKR) of 1.27 Mbit/s, while at 504-km standard fiber, we
obtain the repeater-like key rate scaling with a SKR of 34 times higher than
the repeaterless secret key capacity. Our work provides a scalable and
practical solution to TF-QKD, thus representing an important step towards its
wide applications.
