Quantum radar using entanglement.

Now demonstrated in a lab, for real.

The device is simple in essence. The researchers create pairs of entangled microwave photons using a superconducting device called a Josephson parametric converter. They beam the first photon, called the signal photon, toward the object of interest and listen for the reflection. In the meantime, they store the second photon, called the idler photon. When the reflection arrives, it interferes with this idler photon, creating a signature that reveals how far the signal photon has traveled. Voila -- quantum radar!

This raises the possibility of undetectable radar. Also the possibility of using radar in situations where you need very low luminosity of the radar beam for biological safety.