A team of scientists led by Shabir Barzanj of the Austrian Institute of Science and Technology has designed and tested a radar device that uses a pair of entangled photons as a scanning signal. Thus, they reached a fundamentally new level of quantum technologies, while simultaneously creating the prerequisites for the development of a practical tool based on them. Even now, the prototype of a quantum radar is more sensitive than any military development, although the range of its operation is still small.
The idea is incredibly simple and logical. Using a device called the Josephson Parametric Transducer, Barzanj's colleagues created a pair of entangled microwave photons. One was called "signal" and launched towards the target, the second was called "waiting" and left in place. When the signal photon bounced off the target and came back, it interacted with the waiting photon. Scientists studied the signature of the process, compared the changes in the particles, and calculated the path and distance that the signal photon traveled.
The fundamental feature of such a radar is that a pair of entangled photons has a very strong relationship, so it is easy to track and filter out the effect of background noise on them. Conventional microwave radars work just the opposite - they use the strongest possible signal, which is guaranteed to be able to break through the interference. And this is a significant consumption of energy, and unmasking - and, most importantly, the presence of physical danger for close objects.
In a quantum radar, everything is different, to work it only needs a few pairs of entangled photons with low energy. The temperature in the prototype radar is at the millikelvin level, a few steps from absolute zero, but it detects an object at a distance of 1 meter in a room where at room temperature there are at least 1000 microwave photons in space at the same time, creating background noise. With such sensitivity, it is possible to study the tissues and cells of living beings without the risk of damaging them. Or create a signaling device whose activity is almost impossible to track.