China’s Secure Communications Quantum Leap

In May 2010 a team of 15 Chinese researchers from Tsinghua University in Beijing and the Hefei National Laboratory for Physical Sciences, a government-directed research center, 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 miles 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 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 16 km. 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 U.S. 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: english.cas.cn/Ne/CASE/201006/t20100604_54900.shtml.
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.