  Quantum illumination is a quantum sensing technique where entanglement is
exploited to improve the detection of low-reflectivity targets in a strong
thermal background. In this paper, we study the quantum illumination of
suspected targets under the curved spacetime background of the Earth. It is
counterintuitive to find that to achieve the same error-probability both target
detection scenarios, the illumination strategy curved spacetime consumes less
resources than the flat spacetime strategy. That is to say, the gravitational
effect of the Earth can promote the efficiency of quantum spatial target
detection. This is because the average particle number of the thermal signal
reflected in the curved spacetime is always less than the number in flat
spacetime. We also find that the spatial quantum target detection with
bipartite entangled state is more efficient than the coherent state strategy in
the curved spacetime.
