China's secure communications quantum leap
By Matthew Luce
A team of 15 Chinese researchers from Tsinghua University in Beijing and the
Hefei National Laboratory for Physical Sciences, a government-directed research
center, in May published a research paper announcing a successful demonstration
of "quantum teleportation" (liangzi yinxing chuan) over 16 kilometers of
free space.
These researchers claimed to have the first successful experiment in the world.
The technology on display has the potential to revolutionize secure
communications for military and intelligence organizations and may become the
watershed of a research race in communication and information technology.
Although much of the science behind this technology is still young, quantum
technologies have wide-ranging applications for the fields of cryptography,
remote sensing and secure satellite
communications. In the near future, the results from this experiment will be
used to send encrypted messages that cannot be cracked or intercepted, and
securely connect networks, even in remote areas, with no wired infrastructure,
even incorporating satellites and submarines into the link [1].
Roots in quantum physics, applications in intelligence
Rather than transporting matter from place to place, quantum teleportation's
most practical applications currently involve using photons for instantaneous,
almost totally secure data communication. Using the term "teleportation" to
describe this effect can be justified by what Albert Einstein called "spooky
action at a distance": after two particles are linked together through quantum
entanglement, any change in the state of one particle immediately alters the
other, even from kilometers away. In effect, the state of the particle at the
sender's end is destroyed and reappears as an exact replica at the receiver's
end, with a negligible chance of undetected third-party interception [2].
While the teleportation of physical matter remains science fiction at this
point, quantum teleportation could be immediately implemented as a means for
secure communications and cryptography. Current encryption techniques are based
upon mathematical functions involving very large prime numbers and secure key
management and distribution, but this strategy has a number of drawbacks and is
nearing the end of its shelf life.
In particular, as computing power continues to double every year and computer
bits speed up through the use of quantum particles, the cryptographic keys used
for encoding and decoding must now be changed more often to prevent encrypted
data from being cracked. As a result, it has become very difficult to "future
proof" the encryption of data, and were any major breakthrough in quantum
computing to be achieved in the near future, current encryption techniques
could become obsolete and encrypted data could suddenly become unprotected [3].
The security of using quantum teleportation to distribute cryptographic keys,
on the other hand, is upheld by the laws of physics and has a seemingly
infinite time horizon. These keys cannot currently be detected and cracked even
with the help of the most powerful computers. Owing to the Heisenberg
Uncertainty Principle, the quantum states of photons cannot be observed without
changing the state of the particle, which has the result of immediately
informing the sender and receiver of any eavesdropping. Quantum communication
can thus be used to send the most sensitive information, including keys to
decode encrypted data sent over less secure means.
Significance of the China's achievement
As a result, the issue has found itself at the center of a rapidly developing
geopolitical race to apply quantum technology to military and intelligence
work. Since secure quantum key distribution (QKD) provides a much higher level
of security between communication networks, employing quantum teleportation
over a satellite network allows for completely secure communications, even in
sensitive and remote areas, without fiber optic infrastructure, as long as all
parties are able to maintain line of sight with a satellite. This could have
wide applications in communications and intelligence for ground troops,
aircraft, surface ships and submarines, and fits into China's current plans to
grow its satellite network even further.
Using quantum teleportation to send this type of information has been
technically possible for several years, but according to the Chinese research
paper, it had been previously demonstrated experimentally only over an enclosed
fiber optics network and then only over a distance of several hundred meters
[4].
The Chinese experiment appears to shatter these records by claiming to be the
first to use a high-powered blue laser to exchange quantum information over a
free space channel, and to demonstrate the principle over a distance as great
as 16km. This distance is significant because it displays approximately the
same degree of light distortion as is seen in communication from the earth's
surface to a satellite, and so would allow for quantum communication using
satellites. If this experiment were indeed the first of its kind, it would
appear that China has succeeded in leapfrogging the West, and gained a
significant edge in next-generation communications and cryptography.
A quantum space race?
The Chinese claim to be the first may not be entirely accurate, although
certain elements of their experiment were unique and innovative. In 2005, a
group of universities and defense corporations under a Defense Advanced
Research Projects Agency (DARPA) grant and led by BBN Technologies, the company
responsible for developing the precursor to the Internet, succeeded in
transferring cryptographic keys over a free-space link of 23 km in Cambridge,
Massachusetts.
Well beyond the single link employed by the Chinese, the BBN program has
developed an expanding, multi-node web of secure quantum communication that
will be able to further expand and link seamlessly with existing Internet
technology [5]. There are a few differences in the physics of their experiment
that still make it notable and may not technically disqualify the Chinese from
claiming their status as first, but nonetheless American researchers seem to
have had a five-year head start in demonstrating the principles of the
technology.
However, one notable difference between the Chinese and American experiments is
that the Beijing experiment used a blue laser for their teleportation
experiments while the BBN team had been employing infrared. Both have
advantages and disadvantages in range and power, but the primary difference in
their applications seems to be that blue and blue-green lasers penetrate
further into water and so have wider applications for sub-surface
communications. China is currently modernizing its submarine fleet as a way to
project force further past its coastal waters to deter any US naval response to
a potential invasion of Taiwan as well as doing significant research into laser
communications in submarines [6].
Quantum laser links with satellites would allow sub-surface communication
without most of the traditional downsides of radio communications and allow
subs to operate with even greater autonomy and silence [7]. Judging from the
interest in blue lasers for underwater communication and the interesting choice
of a blue laser for the teleportation experiment, it would be safe to venture a
guess that applications for quantum communication are already beginning to find
their way into Chinese military research and development.
Because of its security level and applications for satellite and submarine
communications, quantum communication technology figures centrally in the
objectives of the Chinese military to upgrade their growing command and control
capabilities. A functional satellite-based quantum communication system would
give the Chinese military the ability to operate further afield without fear of
message interception.
However, Chinese researchers must also be aware of the potential for the United
States to employ the same technology and may be seeking ways to counter this
eventuality. While it is still almost impossible to intercept quantum messages
without being detected, it may be feasible to jam the laser signals that send
them with "optical noise" or other lasers. Understanding the ways in which
quantum cryptography functions may also eventually expose further weaknesses in
the network that can be exploited by a savvy adversary.
China's continuing cutting-edge quantum cryptography, lasers and optics
research thus seems as much a reaction to the same research in the United
States and an attempt to counter it as it is to develop its own indigenous
network.
Conclusions
All of these potential uses are motivations for Chinese labs to be the first to
develop successful applications of quantum technology for immediate deployment
and to claim milestones like being the first to successfully execute
teleportation over several miles of free space.
Besides the military uses and academic prestige, this accomplishment could
attract a significant amount of international funding for China's developing
optics industry, and if quantum teleportation becomes the new paradigm for the
future of secure communications, China would like to make a name for itself as
the premier research and development hub. Claims of this recent "first" for
China then have that much greater significance for security and the continued
health of US technological superiority.
Notes
1. Jin Xian-Min, et al. "Experimental free-space quantum teleportation." Nature
Photonics 4, 376 - 381 (2010). Published online: May 16, 2010
doi:10.1038/nphoton.2010.87. See also the Chinese Academy of Sciences
review.
2. Lei Zhang, Jacob Barhen, and Hua-Kuang Liu. "Experimental and Theoretical
Aspects of Quantum Teleportation." Center foe Engineering Science Advanced
Research, Computer Science and Mathematics Division, Oak Ridge National
Laboratory (2000).
3. David Pearson, "Building a QKD Network out of Theories and Devices," BBN
Technologies (December 2005).
4. The Chinese paper cites R Ursin, et al. "Quantum teleportation across the
Danube" and I Marcikic, et al "Long-distance teleportation of qubits at
telecommunication wavelengths," both descriptions of quantum cryptography over
hundreds of meters of optical fiber.
5. Chip Elliott, et al. "Current status of the DARPA Quantum Network." In
Quantum Information and Computation III, edited by Eric J. Donkor, Andrew R.
Pirich, Howard E. Brandt, Proceedings of SPIE Vol. 5815 (SPIE, Bellingham, WA,
2005).
6. See Yingzhuang Liu and Xiaohu Ge, "Underwater laser sensor network: a new
approach for broadband communication in the underwater." Department of
Electronics & Information Engineering, Huazhong University for Science and
Technology (May 2006).
7. These include detectability, the need to surface to communicate, limitations
in range, and the reliance on cryptographic keys that may be cracked.
Matthew Luce is a researcher and Chinese linguist at Defense Group Inc’s
Center for Intelligence Research and Analysis, where he does primary source
research and analysis of China’s science and technology policies and
development programs. Mr. Luce's research and writing focuses on cyber
security, C4ISR-related technologies, and China's ethnic relations. He has
worked and traveled extensively in China and speaks and reads fluent Chinese.
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