  Distributed quantum sensing can provide quantum-enhanced sensitivity beyond
the shot-noise limit (SNL) for sensing spatially distributed parameters. To
date, distributed quantum sensing experiments have been mostly accomplished in
laboratory environments without a real space separation for the sensors. In
addition, the post-selection is normally assumed to demonstrate the sensitivity
advantage over the SNL. Here, we demonstrate distributed quantum sensing in
field and show the unconditional violation (without post-selection) of SNL up
to 0.916 dB for the field distance of 240 m. The achievement is based on a
loophole free Bell test setup with entangled photon pairs at the averaged
heralding efficiency of 73.88%. Moreover, to test quantum sensing in real life,
we demonstrate the experiment for long distances (with 10-km fiber) together
with the sensing of a completely random and unknown parameter. The results
represent an important step towards a practical quantum sensing network for
widespread applications.
