The end of stealth? New Chinese radar capable of detecting ‘invisible’
targets 100km away
Breakthrough relies on ‘spooky’ phenomenon of quantum entanglement
PUBLISHED : Wednesday, 21 September, 2016, 12:43pm
UPDATED : Wednesday, 21 September, 2016, 11:11pm
Stephen Chen - South China Morning Post
http://www.scmp.com/news/china/article/2021235/end-stealth-new-chinese-radar-capable-detecting-invisible-targets-100km

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.

“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.

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.

This article appeared in the South China Morning Post print edition as:
Quantum radar ‘can see stealth planes at 100km’