A team of four researchers led by Shabir Barzanjeh at the Institute of Science and Technology Austria leveraged entangled microwaves to create the world's first quantum radar (via MIT Technology Review). The device utilizes a handful of photos to detect objects in its surroundings and emits only trace amounts of electromagnetic radiation. This camouflages its signature in background noise making it extremely hard to detect.
At its core, the device works on the principle of Quantum Entanglement, a phenomenon that Einstein deemed "spooky action at a distance", whereby two 'entangled' quantum particles, regardless of their separation, exhibit an instantaneous correlation between certain physical properties intrinsic to each.
For the purpose of creating a quantum radar, the researchers produced pairs of entangled microwave photons (low-energy photons) using a superconducting device called a Josephson parametric converter. They directed the first photon—the signal photon—towards the object that was to be detected and listened for its reflection. A second photon—the idler photon—then interferes with the reflection of the signal photon thereby revealing how far the original photon traveled and hence, the incident object's location.
This allowed Barzanjeh and his team to detect objects within a meter inside a small room with only a handful of photons, something that is impossible for conventional radars as they require powerful electromagnetic radiation emitters to function. On top of boasting low emission requirements, quantum radars also have the added advantage of being able to hide in the microwave background radiation of a small room, and hence remain undetectable to other devices hunting for radars.
The team eyes potential use-cases of quantum radars in biomedical and security applications due to the device's non-invasive nature. Barzanjeh commented on his team's creation by saying:
Our experiment shows the potential as a non-invasive scanning method for biomedical applications, e.g., for imaging of human tissues or non-destructive rotational spectroscopy of proteins.