Cyberattacks are exponentially increasing over time, improving the security of communications is crucial for guaranteeing the protection of sensitive information for states and individuals. For states, securing communications is mandatory for a strategic geopolitical influence.
Quantum technology is considered to be unbreakable and impossible to hack. A unique aspect of quantum cryptography is that Heisenberg’s uncertainty principle ensures that if Eve attempts to intercept and measure Alice’s quantum transmissions to Bob, her activities must produce an irreversible change in the quantum states that are retransmitted to Bob. These changes will introduce an anomalously high error rate in the transmissions between Alice and Bob, allowing them to detect the attempted eavesdropping.
Quantum key distribution (QKD), establishes highly secure keys between distant parties by using single photons to transmit each bit of the key. Photons are ideal for propagating over long-distances in free-space and are thus best suited for quantum communication experiments between space and ground. The unit of quantum information is the “qubit” (a bit of information “stamped” in a quantum physical property, for instance the polarization of a photon).
QKD thus solves the long-standing problem of securely transporting cryptographic keys between distant locations. “Even if the keys were transmitted across hostile territory, their integrity could be unambiguously verified upon receipt,” say Thomas Jennewein, Brendon Higgins and Eric Choi in SPIE.
Fiber optic based QKD systems are commercially available today, however are point to point links and limited to the order of few hundreds kms because of current optical fiber and photon detector technology. Extending the point to point links over long distances would require “quantum repeaters” that are devices that capture and retransmit the quantum information.
One way to overcome this limitation is by bringing quantum communication into space. An international team led by the Austrian physicist Anton Zeilinger has successfully transmitted quantum states between the two Canary Islands of La Palma and Tenerife, over a distance of 143 km. The previous record, set by researchers in China was 97 km. The process called quantum teleportation allows the state of one of the two entangled photons to be changed immediately without delay by changing the state of other photon even though they may be widely separated.
China found another solution by beaming entangled photons through the vacuum of space, so they won’t be absorbed. Quantum satellite can generate quantum keys that can be used to encrypt messages sent between cities thousands of miles apart. On 16th Aug 2016 China launched the world’s first quantum communications satellite officially known as Quantum Experiments at Space Scale, or QUESS, satellite. The launch took place from the Jiuquan Satellite Launch Centre in the Gobi Desert, with a Long March 2D rocket sending the 620 kilogram (1,367 pound) satellite to a 600 kilometer (373 mile) orbit at an inclination of 97.79 degrees.
Micius satellite works by firing a laser through a crystal creating a pair in a state of entanglement. A half of each pair is sent to two separate stations on earth. The satellite serves as the source of pairs of entangled photons, twinned light particles whose properties remain intertwined no matter how far apart they are. If you manipulate one of the photons, the other will be similarly affected at the very same moment. A team of Chinese scientists have realized the satellite-based distribution of entangled photon pairs over 1,200 kilometers. The photon pairs were demonstrated to be still entangled after travelling long distances. The result is the longest entanglement ever demonstrated, and the first that spanned between the Earth and space.
This satellite-based technology opens up bright prospects for both practical quantum communications and fundamental quantum optics experiments at distances previously inaccessible on the ground, said Pan Jianwei, an academician of the Chinese Academy of Sciences. Scientists have now reported using this technology to reach a major milestone: long-range secure communication you could trust even without trusting the satellite it runs through.
“In its two-year mission, QUESS is designed to establish ‘hack-proof’ quantum communications by transmitting uncrackable keys from space to the ground,” Xinhua news agency said. China then plans to put additional satellites into orbit China hopes to complete a QKD system linking Asia and Europe by 2020, and have a worldwide quantum Network.
“The newly-launched satellite marks a transition in China’s role – from a follower in classic information technology development to one of the leaders guiding future achievements,” Pan Jianwei, the project’s chief scientist, told the agency. Quantum communications holds “enormous prospects” in the field of defense, it added.
Based on the QKD technology, Chinese researchers could launch three more small-size satellites in the next three to five years to form a network that can fulfill more quantum communication tasks, a critical step to create the infrastructure of a globalized quantum internet one day, said Yin.
China plans to develop a medium-high-earth-orbit quantum communication satellite able to provide services around the clock in the next few years, Pan Jianwei, member of the 13th National Committee of the Chinese People’s Political Consultative Conference (CPPCC), told CGTN at the press conference for the second session of the 13th CPPCC National Committee in March 2019. When asked about the future plan for quantum communication technology, Pan said his team is planning to design a new one to supplement the Mozi satellite, which can only function at night due to interference from the sun.
In November 2015, at the 18th Party 8 Congress’ 5th Plenum, Xi Jinping included quantum communications in his list of major science and technology projects that are prioritized for major breakthroughs by 2030, given their importance from the perspective of China’s long-term strategic requirement. Many other countries like United States, Canada, Japan, and some EU countries are all racing to develop quantum communication networks as they are virtually un-hackable. Researchers from these countries are closely watching the China’s tests.
According to the Ministry of Science and Technology (MOST), China has made a great number of major new and high-tech achievements during the 13th Five-Year Plan period (2016-2020). Experiments including the quantum science satellite Mozi and the quantum communication line between Beijing and Shanghai conducted by Chinese scientists have enabled the country to build the prototype of the first space-ground integrated quantum communication network, said Qin Yong, director-general of the Department of High and New Technology of the MOST at a press conference held by the State Council Information Office in Oct. 2020.
Satellite QKD Challenges
Satellite based QKD has many challenges. Technically, the lasers being used to beam the entangled photons between the stations will have to achieve a high level of precision to reach the selected targets. Atmospheric inference and movement on the ground obscure their trajectory and delay the synchronization between the two stations. There might be difficulties to minimize attenuation for a long distance. Even if the entanglement occurred, the rate of data transmission for communications via quantum encryption would initially be basic.
The biggest challenge, Alexander Ling, principal investigator at the Centre for Quantum Technologies in Singapore said, is being able to orient the satellite with pinpoint accuracy to a location on Earth where it can send and receive data without being affected by any disturbances in Earth’s atmosphere. Ling said. “You’re trying to send a beam of light from a satellite that’s 500 kilometres (310 miles) above you.”
Record breaking accomplishments of Chinese Quantum Satellite
Micius is the world’s first quantum communications satellite and has, for several years, been at the forefront of quantum encryption. China’s quantum satellite has produced many successful results. It is this property that lies in the heart of the most secure forms of quantum cryptography, the entanglement-based quantum key distribution. If you use one of the entangled particles to create a key for encoding messages, only the person with the other particle can decode them. Then, for good measure, on Sept. 29, 2017, they held a 75-minute videoconference between researchers in the two cities, also encrypted via quantum key.
In the spacecraft’s first record-breaking accomplishment, reported June 16 in Science, the satellite used onboard lasers to beam down pairs of entangled particles, to two cities in China, where the particles were captured by telescopes (SN: 8/5/17, p. 14). The quantum link remained intact over a separation of 1,200 kilometers between the two cities — about 10 times farther than ever before. The feat revealed that the strange laws of quantum mechanics, despite their small-scale foundations, still apply over incredibly large distances.
Next, scientists tackled quantum teleportation, a process that transmits the properties of one particle to another particle (SN Online: 7/7/17). Micius teleported photons’ quantum properties 1,400 kilometers from the ground to space — farther than ever before, scientists reported September 7 in Nature. Despite its sci-fi name, teleportation won’t be able to beam Captain Kirk up to the Enterprise. Instead, it might be useful for linking up future quantum computers, making the machines more powerful.
A Chinese researcher said China’s satellite Quantum Experiments at Space Scale (QUESS) or Micius would work at least two more years beyond its two-year working lifetime and carry out more international cooperation. Yin Juan, a member of the QUESS team who received the annual Newcomb Cleveland Prize in Washington said so in an interview with Xinhua in Jan 2019. In the next two years, the QUESS team is expected to have the inter-continental quantum key distribution experiments with those from Italy, Russia and South Korea.
At the end of 2019, Chinese scientists teamed up with their counterparts from Germany and the Netherlands and realized the Boson sampling quantum computation by feeding 20 photons into a 60×60 mode interferometer for the first time in the world, setting new world records in four key indicators.
Quantum encrypted Video Chat
In 2017, the Micius team used entangled photos to encrypt transmissions enabling a virtual meeting between the Austrian and Chinese science academies in Vienna and Beijing respectively – 7,400km apart. This involved designing the machinery for distributing the keys and a mechanism for preventing malicious attacks, such as blinding the telescopes with other light signals.
Pan’s team has demonstrated a more important and practical capability: the establishment of a secure quantum communication channel between distant parties, the technology that made the quantum-encrypted video chat possible. None of the communication went through Micius. It only produced and distributed the encryption keys. By employing the satellite as a photon emitter and relay, team members in Graz, Austria, and Xinglong, China, developed and shared a 100-kilobyte key that they used to securely exchange photos and hold a video conference. But both ground stations had to talk to and trust Micius as part of their communication systems and use it as a relay before establishing a link with each other.
Micius initiated the link between Graz and Xinglong through a combination of quantum and classical signals, following a version of the BB84 protocol devised by Charles Bennett and Gilles Brassard. The spacecraft created two keys, then sent one to a ground station in Beijing and another to Vienna as it passed overhead. As the satellite passed over a station, it emitted photons that were each prepared in a random polarization state; the station performed one of two polarization measurements on each received photon.
Using the measurement types and results for the exchanged photons, the satellite and station established a unique key. Once Micius developed a key with both stations, it performed a logic operation (specifically, an exclusive OR) on the two strings of bits and sent the results via a classical radio channel to one of the stations. An on-board computer then combined the two secret keys to create a new one, which it beamed down classically.
Armed with their private keys, the Vienna and Beijing teams could unscramble that combined key by essentially subtracting their own, and so learn the other’s secret key. With both keys, one team could decrypt a transmission that the other team encrypted with its key. Pan and Zeilinger used this approach to set up the first intercontinental video chat to be secured in part with a quantum key.
To test the secure connection, the Austrian and Chinese researchers exchanged 5-kilobyte JPEG images that were indecipherable without the shared quantum key. They then used most of the remaining bits of the key to ensure the security of a 75-minute intercontinental video conference In a paper published in the Nov. 17 Physical Review Letters, the researchers performed another type of quantum key distribution, using entangled particles to exchange keys between the ground and the satellite.
A new paper from Pan Jia-Wei’s lab published in Nature shows that Micius has again successfully brought entanglement-based quantum cryptography to its original ground stations 1,200 km apart. But this time the satellite sent simultaneous streams of entangled photons to the ground stations to establish a direct link between the two of them. This gave them robust, unbreakable cryptographic protection without the need to trust the satellite. Until now, this had never been done via satellite or at such great distances.
In the field, point-to-point QKD has been achieved from a satellite to a ground station up to 1,200 kilometres away. However, real-world QKD-based cryptography targets physically separated users on the Earth, for which the maximum distance has been about 100 kilometres. The use of trusted relays can extend these distances from across a typical metropolitan area to intercity and even intercontinental distances. However, relays pose security risks, which can be avoided by using entanglement-based QKD, which has inherent source-independent security. Long-distance entanglement distribution can be realized using quantum repeaters, but the related technology is still immature for practical implementations. The obvious alternative for extending the range of quantum communication without compromising its security is satellite-based QKD, but so far satellite-based entanglement distribution has not been efficient enough to support QKD.
“Here we demonstrate entanglement-based QKD between two ground stations separated by 1,120 kilometres at a finite secret-key rate of 0.12 bits per second, without the need for trusted relays. Entangled photon pairs were distributed via two bidirectional downlinks from the Micius satellite to two ground observatories in Delingha and Nanshan in China. The development of a high-efficiency telescope and follow-up optics crucially improved the link efficiency. The generated keys are secure for realistic devices, because our ground receivers were carefully designed to guarantee fair sampling and immunity to all known side channels24,25. Our method not only increases the secure distance on the ground tenfold but also increases the practical security of QKD to an unprecedented level.”
China has developed the world’s first mobile quantum satellite station
In Jan 2020, it was reported that China’s quantum satellite — Quantum Experiments at Space Scale (QUESS) — has successfully linked up with the world’s first mobile quantum ground station and conducted an encrypted data transmission in Jinan, Shandong Province. The test successfully wrapped up after the ground station received encrypted data from the satellite for nearly eight minutes, said the source.
The mobile quantum ground station, the world’s first of the kind, weighs slightly over 80 kg. It was jointly developed by the University of Science and Technology of China, QuantumCTek Co., Ltd. and the Jinan Institute of Quantum Technology. The ground station used at the launch of QUESS weighed more than 10 tonnes. Researchers have been trying to reduce its size. The latest mobile version can be installed on a vehicle and the manufacturing cost has been significantly reduced. An experimental quantum communication network in Jinan has been connected to the Beijing-Shanghai backbone network, the world’s first secure quantum communication backbone network.
China’s Quantum Satellite Mission Objectives
The major goal is to test the possibilities of relaying quantum “keys” carried by photons, or light particles, over 500 to 1,200 kilometers from a satellite to ground stations to create a new kind of information transmission network that cannot be hacked without detection. The satellite will enable secure communications between Beijing and Urumqi, Xinhua said. Other missions include quantum teleportation and quantum entanglement, both for the first time in space.
“Initial tests on the satellite have reached a transmission rate that will allow us to finish these experiments within several weeks, so we will have time to add new experiments,” Pan said. He said the plans include more complex quantum tests between Micius and five ground stations across China this year, and then cross-continental quantum communication experiments to establish links with ground stations in Austria, Italy and Canada in 2018.
Pan Jianwei, the projects’ chief scientist also said that the 2,000-km quantum communication main network between Beijing and Shanghai will be fully operational in the second half of this year. The network would be used by the central government, military and critical business institutions like banks. Government agencies and banks in cities along the route can use it first.
“There are many bottlenecks in the information security. The Edward Snowden case has told us that the information in the transmission networks are exposed to risks of being monitored and being attacked by hackers,” Pan said. In 2012, Pan’s group built the world’s first metropolitan area quantum network in Hefei, linking 46 nodes to allow real-time voice communications, text messages and file transfers. The quantum satellite is part of the country’s Strategic Priority Program on Space Science that started in 2011 and planned to launch four satellites by the end of the year.
The 620kg QUES satellite would seek breakthroughs in cryptography and test laws of quantum mechanics like teleportation and quantum entanglement on a global scale. The experimental satellite would contain a quantum key communicator, quantum entanglement emitter, entanglement source, processing unit and a laser communicator.
The aim of the new experiment conducted by a team led by physicist Pan Jian-Wei from the University of Science and Technology of China in Hefei is: “To see if we can establish quantum key distribution [the encoding and sharing of a secret cryptographic key using the quantum properties of photons between a ground station in Beijing and the satellite, and between the satellite and Vienna. Then we can see whether it is possible to establish a quantum key between Beijing and Vienna, using the satellite as a relay.”
The second step will be to perform long-distance entanglement distribution, over about 1,000 kilometres. We have technology on the satellite that can produce pairs of entangled photons. We beam one photon of an entangled pair to a station in Delingha, Tibet, and the other to a station in Lijiang or Nanshan. The distance between the two ground stations is about 1,200 kilometres. Previous tests were done on the order of 100 kilometres.
“In principle, quantum entanglement can exist for any distance. But we want to see if there is some physical limit… we hope to build some sort of macroscopic system in which we can show that the quantum phenomena can still exist,” Pan told Nature, in describing the theoretical premises for the experiment. This could potentially facilitate super-fast, long-range communications, as well as lead to the creation of unbreakable quantum communication networks.
China has collaborated with the Austrian Academy of Sciences to provide the optical receivers at a ground station in Vienna, while three more stations have also been planned across Austria. Eventually, the Chinese team is planning to launch about 10 additional satellites, which would fly in formation to allow for coverage across more areas of the globe.
Global Satellite Quantum Network
Secure long-distance links such as this one will be the foundation of the quantum internet, the future global network with added security powered by laws of quantum mechanics, unmatched by classical cryptographic methods. Pan Jian-Wei credited Edward Snowden’s 2013 disclosures of internet surveillance by western governments with prompting China to boost quantum cryptography research in order to create more secure means of communication. As a result, Micius has been dubbed Sputnik for the ultra-paranoid.
China is also first country to release a detailed schedule to put this technology to large-scale use. Communications satellite would be a first step toward building a quantum communications network in the sky. China hopes to complete a Asia-Europe intercontinental quantum key distribution in 2020 and build a global quantum communication network by 2030.
The team’s future plans also include making use of China’s future space station, Tiangong, which is expected to be created by the end of the decade, to conduct “upgraded” quantum experiments. “We will have a quantum experiment on the space station and it will make our studies easier because we can from time to time upgrade our experiment (unlike on the quantum satellite).
The network of quantum satellites (2030 China Project) is aiming to increase the record distance for successful quantum entanglement between two points on Earth.
Quantum Communication between Earth and Moon
In the future, Pan also hopes to create a signal transmitting system that could facilitate communication between the Earth and the Moon. “In the future, we also want to see if it is possible to distribute entanglement between Earth and the Moon. We hope to use the [China’s Moon program] to send a quantum satellite to one of the gravitationally-stable points in the Earth-Moon system,” he told the weekly.
“I think China has an obligation not just to do something for ourselves — many other countries have been to the Moon, have done manned spaceflight — but to explore something unknown,” Pen said. The scientist also predicted that the world will soon enter a quantum era with a revolution in quantum physics taking the world by storm and leading to the creation of super-fast quantum computers and large quantum communication networks, China’s People’s Daily reported.
The launch of Micius and the records set by the scientists and engineers building quantum communication systems with its help have been compared to the effect Sputnik had on the space race in the 20th century. In a similar way, the quantum race has political and military implications that are hard to ignore.
“China is completely capable of making full use of quantum communications in a regional war,” China’s leading quantum-communications scientist, Pan Jianwei, said. “The direction of development in the future calls for using relay satellites to realize quantum communications and control that covers the entire army.”
Matthew Luce, a researcher with Defense Group Inc.’s Center for Intelligence Research and Analysis, thinks “A functional satellite-based quantum communication system would give the Chinese military the ability to operate further afield without fear of message interception.”
Militaries have become dependent on Satellites that provide intelligence of adversary’s activities by capturing high resolution images, radar and communication signals, providing wide area real time communications among battle troops and command and control. However, Satellites are vulnerable to jamming, cyber-attacks and other ASAT weapons. China is also developing technologies like electronic warfare, DEW and other ASAT weapons that can disrupt its adversary’s satellites. By developing satellite based quantum cryptology China shall be able to gain information superiority over other countries as it would be able to collect, process, and disseminate an uninterrupted flow of information while exploiting or denying its adversary’s ability to do the same.
Although the Chinese government has not revealed the projects budget, scientists told state media that the construction cost would be ¥100m (£10.17m) for every 10,000 users, according to the South China Morning Post.
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