Quantum Experiments at Space Scale (QUESS; Chinese: 量子科学实验卫星; pinyin: Liàngzǐ kēxué shíyàn wèixīng; lit. 'Quantum Science Experiment Satellite'), is a Chinese research project in the field of quantum physics. QUESS was launched on 15 August 2016.
QUESS is a proof-of-concept mission designed to facilitate quantum optics experiments over long distances to allow the development of quantum encryption and quantum teleportation technology.[8][9][10][11][5] Quantum encryption uses the principle of entanglement to facilitate communication that can absolutely detect whether a third party has intercepted a message in transit thus denying undetected decryption. By producing pairs of entangled photons, QUESS will allow ground stations separated by many thousands of kilometres to establish secure quantum channels.[3] QUESS itself has limited communication capabilities: it needs line-of-sight, and can only operate when not in sunlight.[12]
Further Micius satellites were planned, including a global network by 2030.[12][13]
The mission cost was around US$100 million in total.[2]
Once experiments within China concluded, QUESS created an international QKD channel between China and the Institute for Quantum Optics and Quantum Information, Vienna, Austria − a ground distance of 7,500 km (4,700 mi), enabling the first intercontinental secure quantum video call in 2016.[3][4]
Launch
The launch was initially scheduled for July 2016, but was rescheduled to August, with notification of the launch being sent just a few days in advance.[16] The spacecraft was launched by a Long March 2D rocket from Jiuquan Launch Pad 603, Launch Area 4 on 17 August 2016, at 17:40 UTC (01:40 local time).[2]
Multi-payload mission
The launch was a multi-payload mission shared with QUESS, LiXing-1 research satellite, and ³Cat-2 Spanish science satellite.
LiXing-1: LiXing-1 is a Chinese satellite designed to measure upper atmospheric density by lowering its orbit to 100–150 km. Its mass is 110 kg. On 19 August 2016, the satellite reentered into the atmosphere, so the mission is closed.
³Cat-2: The 3Cat-2 (spelled "cube-cat-two") is the second satellite in the 3Cat series and the second satellite developed in Catalonia at Polytechnic University of Catalonia’s NanoSat Lab. It is a 6-Unit CubeSat flying a novel GNSS Reflectometer (GNSS-R) payload for Earth observation. Its mass is 7.1 kg.
The main instrument on board QUESS is a "Sagnac effect" interferometer.[3] This is a device that generates pairs of entangled photons, allowing one of each to be transmitted to the ground. This will allow QUESS to perform Quantum key distribution (QKD) – the transmission of a secure cryptographic key that can be used to encrypt and decrypt messages – to two ground stations. QKD theoretically offers truly secure communication. In QKD, two parties who want to communicate share a random secret key transmitted using pairs of entangled photons sent with random polarization, with each party receiving one-half of the pair. This secret key can then be used as a one-time pad, allowing the two parties to communicate securely through normal channels. Any attempt to eavesdrop on the key will disturb the entangled state in a detectable way.[13] QKD has been attempted on Earth, both with direct line-of-sight between two observatories, and using fibre optic cables to transmit the photons. However, fiber optics and the atmosphere both cause scattering, which destroys the entangled state, and this limits the distance over which QKD can be carried out. Sending the keys from an orbiting satellite results in less scattering, which allows QKD to be performed over much greater distances.[3]
QUESS is the first spacecraft launched capable of generating entangled photons in space,[5] although transmission of single photons via satellites has previously been demonstrated by reflecting photons generated at ground-based stations off orbiting satellites.[23] While not generating fully entangled photons, correlated pairs of photons have been produced in space using a cubesat by the National University of Singapore and the University of Strathclyde.[23] A German consortium has performed quantum measurements of optical signals from the geostationaryAlphasatLaser Communication Terminal.[24] The US Defense Advanced Research Projects Agency (DARPA) launched the Quiness macroscopic quantum communications project to catalyze the development of an end-to-end global quantum internet in 2012.
In 2024, ESA intends to launch the Eagle-1 quantum key distribution satellite, with a goal similar to that of the Chinese QUESS. It will be part of the development and deployment of the European Quantum Communication Infrastructure (EuroQCI).[25]
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
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