  In this paper, we employ theoretical and experimental efforts and realize a
proof-of-principle verification of device-independent QKD based on the photonic
setup. On the theoretical side, we enhance the loss tolerance for real device
imperfections by combining different approaches, namely, random post-selection,
noisy preprocessing, and developed numerical methods to estimate the key rate
via the von Neumann entropy. On the experimental side, we develop a
high-quality polarization-entangled photon source achieving a state-of-the-art
(heralded) detection efficiency about 87.5%. This efficiency outperforms
previous photonic experiments involving loophole-free Bell tests. Together, we
show that the measured quantum correlations are strong enough to ensure a
positive key rate under the fiber length up to 220 m. Our photonic platform can
generate entangled photons at a high rate and in the telecom wavelength, which
is desirable for high-speed generation over long distances. The results present
an important step towards a full demonstration of photonic device-independent
QKD.
