  The benefits of entanglement can outlast entanglement itself. In quantum
illumination, entanglement is employed to better detect reflecting objects in
environments so noisy that all entanglement is destroyed. Here, we show that
quantum discord - a more resilient form of quantum correlations - explains the
resilience of quantum illumination. We introduce a quantitative relation
between the performance gain in quantum illumination and the amount of discord
used to encode information about the presence or absence of a reflecting
object. This highlights discord's role preserving the benefits of entanglement
in entanglement breaking noise.
