US researchers create Unjammable Radar, that could detect all Stealth planes

U.S. researchers have employed the quantum properties of photons to create an unjammable radar signal. Conventional radar is vulnerable to a range of technologies, ranging from dropping chaff to create false reflections to drowning the radar frequency with noise.

 More sophisticated radar can deal with such ploys, but the most sophisticated radar jammers are able to intercept the the signals and send back false information. However, a team from the University of Rochester, New York have shown how the quantum properties of photons can be used to outsmart this advanced stealth technology. The new radar concept relies on the fact that any attempt to measure a photon always destroys its quantum properties, MIT's Technology Review explains.

 To exploit this curious property, the Rochester team suggest using polarised photons to detect and image objects. If a stealth aircraft attempts to intercept these photons and resend them in a way that disguises its position, it would inevitably change the photons' quantum properties revealing any interference.

 'In order to jam our imaging system, the object must disturb the delicate quantum state of the imaging photons, thus introducing statistical errors that reveal its activity,' the researchers say in a paper published in the journal Applied Physics Letters.

 The technology works in a similar way to quantum key distribution for cryptography, where any eavesdropper would change the quantum properties of the key by listening in, revealing his or her presence. Mehul Malik, who led the team that carried out the research at Rochester's Institute of Optics, tested the concept by bouncing photons off a stealth bomber-shaped target and measuring the return signal's polarisation error rate.

 The system easily imaged the war plane without any eavesdropping, but when the adversary intercepted the signal and modified it to send back the image of a bird, the radar was easily able to see through the ruse. 'That’s an impressive demonstration of the first imaging system that is unjammable thanks to quantum mechanics,' says MIT Technology Review's Physics arXiv blog. However, the researchers admit that their novel radar system is still not perfect. As MIT's blogger explains, it suffers from the same limitations that plagued early quantum cryptographic systems.

 The quantum radar sends photons in pulses that contain several of the quantum particles, one or more of which could be easily siphoned away and replicated to tune the signal sent back to the same state as the one sent.

 'Further, a sophisticated jammer may use quantum teleportation to teleport the polarisation state of our querying photons onto photons carrying false position or time information,' says the study. However, while the equipment needed to carry out such sophisticated jamming is readily available in labs worldwide, it is not thought yet to be deployed by the military.