  Lloyd [1] proved that a large performance gain accrues from use of
entanglement in single-photon target detection within a lossy, noisy
environment when compared to what can be achieved with unentangled
single-photon states. We show that the performance of Lloyd's "quantum
illumination" system is, at best, equal to that of a coherent-state
transmitter, and may be substantially worse. Nevertheless, as shown in [2],
quantum illumination may offer a significant performance gain when operation is
not limited to the single-photon regime.
