  A plethora of applications hinge on a network or an array of sensors to
undertake measurement tasks. A rule of thumb for sensing is that a collective
measurement taken by $M$ independent sensors can improve the sensitivity by
$1/\sqrt{M}$, known as the standard quantum limit (SQL). Quantum resources such
as entanglement and squeezed light can be harnessed to surpass the SQL.
Distributed quantum sensing is an emerging subject dedicated to investigating
the performance gain enabled by entangled states shared by multiple sensors in
tackling different measurement problems. This Review formulates distributed
quantum sensing from a quantum-information perspective and describes
distributed quantum sensing protocols and their experimental demonstrations.
The applications enabled by distributed quantum sensing and an outlook for
future opportunities will also be discussed.
