  The use of entangled light to illuminate objects is shown to provide
significant enhancements over unentangled light for detecting and imaging those
objects in the presence of high levels of noise and loss. Each signal sent out
is entangled with an ancilla, which is retained. Detection takes place via an
entangling measurement on the returning signal together with the ancilla.
Quantum illumination with e bits of entanglement increases the effective
signal-to-noise ratio of detection and imaging by a factor of 2^e, an
exponential improvement over unentangled illumination.
