China announces quantum-entanglement radar
The end of stealth? New Chinese radar capable of detecting ‘invisible’ targets 100km away
A B-2 Stealth Bomber pulls up on the runway after landing at the Palmdale Aircraft Integration Center of Excellence in Palmdale, California.Frederic J. Brown | AFP | Getty Images   A top Chinese military technology company shocked physicists  around the world this week when it announced it had developed a  new form of radar able to detect stealth planes 100km away.  The breakthrough relies on a ghostly phenomenon known as quantum  entanglement, which Albert Einstein dubbed "spooky action at a  distance".  China Electronics Technology Group Corporation (CETC), one of the  "Top 10" military industry groups controlled directly by the  central government, said on Sunday that the new radar system's  entangled photons had detected targets 100km away in a recent  field test.  That's five times the "potential range" of a laboratory prototype  jointly developed by researchers from Canada, Germany, Britain  and the United States last year.  America's Defence Advanced Research Projects Agency has  reportedly funded similar research and military suppliers such as  Lockheed Martin are also developing quantum radar systems for  combat purposes, according to media reports, but the progress of  those military projects remains unknown.  In a statement posted on its website on Sunday, CETC  said China's  first "single-photon quantum radar system" had "important  military application values" because it used entangled photons to  identify objects "invisible" to conventional radar systems.  Nanjing University physicist Professor Ma Xiaosong, who has  studied quantum radar, said he had "not seen anything like this  in an open report".  "The effective range reported by the international research  community falls far below 100km," he said.  A military radar researcher at a university in northwestern China  said the actual range of the new radar could be even greater than  that announced by CETC.  More from the South China Morning Post  : Teleportation, the next  generation: Chinese and Canadian scientists closer to a quantum  internet  'Handshake' shows China's  quantum satellite performing even better than expected, says  scientist    China's hack-proof quantum satellite leap into space leads the  world  "The figure in declassified documents is usually a tuned-down  version of the real [performance]," he said. "The announcement  has gone viral [in the radar research community]."  The scientists said they were shocked because, until recently,  the idea of quantum radar had remained largely confined to  science fiction.  Quantum physics says that if you create a pair of entangled  photons by splitting the original photon with a crystal, a change  to one entangled photon will immediately affect its twin,  regardless of the distance between them.  A quantum radar, generating a large number of entangled photon  pairs and shooting one twin into the air, would be capable of  receiving critical information about a target, including its  shape, location, speed, temperature and even the chemical  composition of its paint, from returning photons.  That sounds similar to a normal radar, which uses radio waves,  but quantum radar would be much better at detecting stealth  planes, which use special coating materials and body designs to  reduce the radio waves they deflect, making them  indistinguishable from the background environment.  In theory, a quantum radar could detect a target's composition,  heading and speed even if managed to retrieve just one returning  photon. It would be able to fish out the returning photon from  the background noise because the link the photon shared with its  twin would facilitate identification.U.S. soldiers stand guard near a U.S. F-22 stealth fighter.Jeon Heon-Kyun | Pool | Getty Images   However, Ma, who was not involved with the CETC project, said  serious technical challenges had long confined quantum radar  technology to the laboratory.  The photons had to maintain certain conditions – known as  quantum states – such as upward or downward spin to remain  entangled. But Ma said the quantum states could be lost due to  disturbances in the environment, a phenomenon known as  "decoherence", which increased the risk of entanglement loss as  the photons travelled through the air, thus limiting the  effective range of quantum radar.  The CETC breakthrough benefited largely from the recent rapid  development of single-photon detectors, which allowed researchers  to capture returning photons with a high degree of efficiency.  CETC said the quantum radar's advantage was not limited to the  detection of stealth planes.  The field test had opened a "completely new area of research", it  said, with potential for the development of highly mobile and  sensitive radar systems able to survive the most challenging  combat engagements.  Quantum radar systems could be small and would be able to evade  enemy countermeasures such anti-radar missiles because the  ghostly quantum entanglement could not be traced, it said.  The company said it had worked with quantum scientists at the  University of Science and Technology of China in Hefei, Anhui  province, where many quantum technology breakthroughs have been  achieved, including the world's longest quantum key distribution  network for secured communication and the development of the  world's first quantum satellite.   Follow CNBC International on Twitter and Facebook.