China launched the world’s first quantum communications satellite officially known as Quantum Experiments at Space Scale, or QUESS, satellite. The launch took place at 17:40 UTC Monday (16th Aug 2016) 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. “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 overall performance has been much better than we expected, which will allow us to conduct all our planned experiments using the satellite ahead of schedule and even add some extra ones,” Pan Jianwei, chief scientist for the satellite project, said at a ceremony.
“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.
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. 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.”
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.
Satellite Mission Objectives
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.
“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.
Global Satellite Quantum Network
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).
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.
UK and Singapore’s Quantum satellite device tests technology for global quantum network
Researchers from the National University of Singapore (NUS) and the University of Strathclyde, UK, have become the first to test in orbit technology for satellite-based quantum network nodes.
They have put a compact device carrying components used in quantum communication and computing into orbit. Their device, dubbed SPEQS, creates and measures pairs of light particles, called photons. Results from space show that SPEQS is making pairs of photons with correlated properties – an indicator of performance.
Team-leader Alexander Ling, an Assistant Professor at the Centre for Quantum Technologies (CQT) at NUS said, “This is the first time anyone has tested this kind of quantum technology in space.” The team had to be inventive to redesign a delicate, table-top quantum setup to be small and robust enough to fly inside a nanosatellite only the size of a shoebox. The whole satellite weighs just 1.65-kilogramm.
The group’s first device is a technology pathfinder. It takes photons from a BluRay laser and splits them into two, then measures the pair’s properties, all on board the satellite. To do this it contains a laser diode, crystals, mirrors and photon detectors carefully aligned inside an aluminum block. This sits on top of a 10 centimetres by 10 centimetres printed circuit board packed with control electronics.
Further testing and refinement may lead to a way to use entangled photons beamed from satellites to connect points on opposite sides of the planet. A fleet of nanosatellites carrying sources of entangled photons would be used to enable private encryption keys between any two points on Earth.
Even with the success of the more recent mission, a global network is still a few milestones away. The team’s roadmap calls for a series of launches, with the next space-bound SPEQS slated to produce entangled photons. SPEQS stands for Small Photon-Entangling Quantum System.
With later satellites, the researchers will try sending entangled photons to Earth and to other satellites. The team are working with standard “CubeSat” nanosatellites, which can get relatively cheap rides into space as rocket ballast. Ultimately, completing a global network would mean having a fleet of satellites in orbit and an array of ground stations.
In the meantime, quantum satellites could also carry out fundamental experiments – for example, testing entanglement over distances bigger than Earth-bound scientists can manage. “We are reaching the limits of how precisely we can test quantum theory on Earth,” said co-author Dr Daniel Oi at the University of Strathclyde.
Canada ‘s University of Waterloo Institute for Quantum Computing (IQC) carried out Airborne demonstration of a Satellite quantum key distribution
In a study published in Quantum Science and Technology, researchers from the University of Waterloo have shown that it’s possible to transmit quantum information from a ground station to a moving aircraft. “Here, we demonstrate QKD from a ground transmitter to a receiver prototype mounted on an airplane in flight. We have specifically designed our receiver prototype to consist of many components that are compatible with the environment and resource constraints of a satellite. Coupled with our relocatable ground station system, optical links with distances of 3–10 km were maintained and quantum signals transmitted while traversing angular rates similar to those observed of low-Earth-orbit satellites.”
The system was tested using an aircraft that mimicked how high or low a satellite might appear in the sky. The aircraft, with the name Twin Otter, carried out 14 passes over the facility at varying distances. Only half of the passes were successful in establishing a quantum link, and in six out of those seven passes, the team was successful in extracting the quantum key.
“This is an extremely important step that finally demonstrates our technology is viable,” team leader Professor Thomas Jennewein added. “We achieved optical links at similar angular rates to those of low-Earth-orbit satellites, and for some passes of the aircraft over the ground station, links were established within 10 seconds of position data transmission. We saw link times of a few minutes and received quantum bit error rates typically between three and five percent, generating secure keys up to 868 kb in length.”
Under similar conditions, the uplink configuration has a lower key generation rate than the downlink, owing to atmospheric turbulence affecting the beam path earlier in the propagation. Importantly, an uplink also possesses a number of advantages over a downlink, including relative simplicity of the satellite design, not requiring high-rate true random number generators, relaxed requirements on data processing and storage (only the photon reception events need be considered, which are many orders of magnitude fewer than the source events), and the flexibility of being able to incorporate and explore various different quantum source types with the same receiver apparatus (which would have major associated costs were the source located on the satellite, as for downlink).
Recently, China launched a quantum science satellite that aims to perform many quantum experiments with optical links between space and ground. However its exact capabilities are unverified as no details or results have been published at this time.
Earlier a team led by Professor Thomas Jennewein at the University of Waterloo’s Institute for Quantum Computing (IQC) completed a successful laboratory demonstration of a form, fit and function prototype of a Quantum Key Distribution Receiver (QKDR) suitable for airborne experiments and ultimately Earth orbiting satellite missions.
The team designed and built the QKDR under a $600,000 contract from the Canadian Space Agency (CSA). The prototype QKDR needed to accommodate the payload constraints of a microsatellite-class mission. That included using only 10 W of power and weighing less than 12 kg.
Through radiation testing at TRIUMF located at the University of British Columbia, it was shown that with adequate shielding and cooling the QKDR detector devices can survive and operate in the space radiation environment for at least one year and possibly up to 10 years. The team also defined a credible path-to-flight for all key technologies including the miniaturized integrated optics, detectors and data processing electronics for the satellite payload.
Utilising orbiting satellites, therefore, has potential to allow the establishment of global QKD networks, with ‘quantum’ satellites acting as intermediaries. Such satellites could operate as untrusted nodes linking two ground stations simultaneously, or trusted nodes connecting any two ground stations on Earth at different times
QEYSSat (Quantum EncrYption and Science Satellite) microsatellite mission
Researchers from University of Waterloo have proposed microsatellite mission called QEYSSat (Quantum EncrYption and Science Satellite) through a series of conceptual and technical studies funded primarily by the Canadian Space Agency (CSA). QEYSSat’s mission objectives are to demonstrate the generation of encryption keys through the creation of quantum links between ground and space, and also to conduct fundamental science tests of long-distance quantum entanglement (the intriguing phenomenon in which the joint quantum state of, for example, two particles cannot be factored into a product of individual particle states).
“The quantum signals for QEYSSat will be generated in photon sources located on the ground. An optical transmitter on the ground will point the beam of photons toward the satellite. (QKD can be carried out via such quantum uplinks, along with ordinary classical communication with the satellite,” said the researchers. An important aspect of this mission concept is to keep the complex source technologies on the ground and ensure that the satellite is simple and cost-effective. This approach also allows the quantum link to be implemented using various different types of quantum sources, including entangled photons and weak coherent pulses.
“Placing the quantum receiver in space, however, poses some technical challenges of its own. In particular, the expected link losses will be higher for the uplink than they would be for a downlink because atmospheric turbulence perturbs the photons at the start of their journey up to the satellite. In addition, the dark counts of single-photon detectors will rise due to radiation exposure in orbit,” write the researchers in SPIE.
The current platform for the QEYSSat mission proposal is based on a microsatellite, to be located in a low Earth orbit at an altitude of about 600km. The payload would have an optical receiver with 40cm aperture as the main optics.
“The QEYSSat payload will include the capability to analyze and detect single optical photons with high efficiency and accuracy. Each arriving photon will be analyzed in a polarization analyzer and detected in single-photon detectors. Onboard data acquisition will register all detection events and record their time-stamps to subnanosecond precision, for processing later on the ground.”
To show the viability of this mission concept, Researchers have conducted several theoretical and experimental studies, including a comprehensive link performance analysis, as well as QKD experiments over high transmission losses and over a rapidly fluctuating channel.
Typical QKD experiments operate with 20–30dB of losses, but for a satellite link the losses are expected to be about 40dB or more. Researchers studied how to implement a QKD protocol in the case of such high transmission losses and operated a system successfully with losses up to nearly 60dB.
“Fluctuations caused by turbulence will be particularly important when sending quantum signals to a satellite. We showed that quantum communication using single photons is still possible even when the channel transmission is strongly fluctuating, down to complete drop outs of the signal. We also showed that in the extreme case of very high transmission losses, we can improve the signal-to-noise ratio and keep performing QKD by applying a threshold filter to the data in post-processing,” write the researchers in SPIE.
European scientists have proposed a quantum communications experiment that could be sent to the international space station.
Satellite based Quantum Communications
Satellite-based quantum communication systems offer an approach for surpassing distance limitations even with today’s technology, and make a truly global network for quantum communication feasible in the near term.
However, the demonstration of the feasibility of such links is crucial for designing space payloads and to eventually enable the realization of protocols such as quantum-key-distribution (QKD) and quantum teleportation along satellite-to-ground or intersatellite links.
The Chinese satellite experiment faces many technical challenges: “The satellite will fly so fast (it takes just 90 minutes to orbit Earth) and there will be turbulence and other problems — so the single-photon beam can be seriously affected. Also we have to overcome background noise from sunlight, the Moon and light noise from cities, which are much stronger than our single photon,” said Pan.
Researchers have already demonstrated the faithful transmission of qubits from space to ground by exploiting satellite corner cube retroreflectors acting as transmitter in orbit, obtaining a low error rate suitable for QKD. A key factor is the error rate in this process, if the error rate is above 11 percent, quantum cryptography does not work.
Free Space QKD systems
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.
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.
Quantum Key Distribution
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.
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