Satellite-Based Quantum Encryption Network

The successful characterization of quantum features is a precondition for the implementation of a global quantum communication network using satellites. (Source: Google / ESA / OSA)

Researchers demonstrate ground-based measure­ments of quantum states sent by a laser aboard a satel­lite 38,000 kilo­meters above Earth. This is the first time that quantum states have been measured so care­fully from so far away. “We were quite surprised by how well the quantum states survived traveling through the atmo­spheric turbu­lence to a ground station,” said Christoph Marquardt from the Max Planck Insti­tute for the Science of Light, Germany. “That technology on satellites, already space-proof against severe environ­mental tests, can be used to achieve quantum-limited measure­ments, thus making a satel­lite quantum commu­nication network possible. This greatly cuts down on develop­ment time, meaning it could be possible to have such a system as soon as five years from now.”

A satellite-based quantum-based encryp­tion network would provide an extremely secure way to encrypt data sent over long distances. Deve­loping such a system in just five years is an extremely fast timeline since most satellites require around 10 years of develop­ment. Normally, every component from computers to screws must be tested and approved to work in the harsh environ­mental conditions of space and must survive the gravi­tational changes experienced during the launch.

Today, text messages, banking trans­actions and health infor­mation are all encrypted with techniques based on mathe­matical algo­rithms. This approach works because it is extremely difficult to figure out the exact algorithm used to encrypt a given piece of data. However, experts believe that computers powerful enough to crack these encryp­tion codes are likely to be available in the next 10 to 20 years. The looming security threat has placed more attention on imple­menting stronger en­cryption techniques such as quantum key distribution. Rather than relying on math, quantum key distri­bution uses pro­perties of light particles known as quantum states to encode and send the key needed to decrypt encoded data. If someone tries to measure the light particles to steal the key, it changes the par­ticles’ behavior in a way that alerts the intended commu­nicating parties that the key has been compromised and should not be used. The fact that this system detects eaves­dropping means that secure communi­cation is guaranteed.

Although methods for quantum encryp­tion have been in deve­lopment for more than a decade, they don’t work over long distances because residual light losses in optical fibers used for tele­communications networks on the ground degrade the sensitive quantum signals. Quantum signals cannot be also rege­nerated without altering their properties by suing optical ampli­fiers as it is done for classical optical data. For this reason, there has been a recent push to develop a satel­lite-based quantum communi­cation network to link ground-based quantum encryption networks located in different metro­politan areas, countries and continents.

Although the new findings showed that quantum communi­cation satellite networks do not need to be designed from scratch, Marquardt notes that it will still take 5 to 10 years to convert ground based systems to quantum-based encryption to communi­cate quantum states with the satel­lites. For the experiments, Marquardt’s team worked closely with satellite tele­communi­cations company Tesat-Spacecom GmbH and the German Space Admi­nistration. The German Space Adminis­tration previously contracted with Tesat-Spacecom on behalf of the German Ministry of Economics and Energy to develop an optical communi­cations tech­nology for satellites. This technology is now being used commercially in space by laser communi­cation terminals onboard Coper­nicus, the European Union’s Earth Obser­vation Programme, and by Space­Data­Highway, the European data relay satellite system.

It turned out that this satellite optical communi­cations tech­nology works much like the quantum key distri­bution method developed at the Max Planck Insti­tute. Thus, the researchers decided to see if it was possible to measure quantum states encoded in a laser beam sent from one of the satel­lites already in space. In 2015 and the beginning of 2016, the team made these measure­ments from a ground-based station at the Teide Observatory in Tenerife, Spain. They created quantum states in a range where the satellite normally does not operate and were able to make quantum-limited measure­ments from the ground.

“From our measure­ments, we could deduce that the light traveling down to Earth is very well suited to be operated as a quantum key distribution network,” Marquardt said. “We were surprised because the system was not built for this. The engineers had done an excellent job at opti­mizing the entire system.” The researchers are now working with Tesat-Spacecom and others in the space industry to design an upgraded system based on the hardware already used in space. This will require upgrading the laser communi­cation design, incor­porating a quantum-based random number generator to create the random keys and inte­grating post processing of the keys. “There is serious interest from the space industry and other orga­nizations to implement our scientific findings,” said Marquardt. “We, as funda­mental scientists, are now working with engineers to create the best system and ensure no detail is overlooked.” (Source: OSA)

Reference: K. Günthner et al.: Quantum-limited measurements of optical signals from a geostationary satellite, Optica 4, 611 (2017); DOI: 10.1364/OPTICA.4.000611

Link: Quantum Information Processing, Max-Planck-Institute for the Science of Light, Erlangen, Germany

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