| Names | Quantum Space Satellite Micius /Mozi |
|---|---|
| Mission type | Technology demonstrator |
| Operator | Chinese Academy of Sciences |
| COSPAR ID | 2016-051A[1] |
| SATCATno. | 41731 |
| Mission duration | 2 years (planned) 8 years, 11 months, 5 days(in progress) |
| Spacecraft properties | |
| Manufacturer | Chinese Academy of Sciences |
| BOL mass | 631 kg (1,391 lb) |
| Start of mission | |
| Launch date | 15 August 2016, 17:40 UTC[2] |
| Rocket | Long March 2D |
| Launch site | JiuquanLA-4 |
| Contractor | Shanghai Academy of Spaceflight Technology |
| Orbital parameters | |
| Regime | Sun-synchronous |
| Perigee altitude | 488 km (303 mi)[2] |
| Apogee altitude | 584 km (363 mi)[2] |
| Inclination | 97.4 degrees[2] |
| Transponders | |
| Band | Ultraviolet[3] |
| Instruments | |
| Sagnacinterferometer | |
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.
The project consists of the satelliteMicius, orMozi (Chinese:墨子), after the ancient Chinese philosopher, operated by theChinese Academy of Sciences, as well as ground stations in China. TheUniversity of Vienna and theAustrian Academy of Sciences are running the satellite's European receiving stations.[4][5] The satellite conducted Space-Earthquantum key distribution (Chinese:量子密钥分发) experiments, facilitated by laser communications experiment carried onTiangong-2 space laboratory module.[6][7]
QUESS is a proof-of-concept mission designed to facilitatequantum optics experiments over long distances to allow the development ofquantum encryption andquantum teleportation technology.[8][9][10][11][5] Quantum encryption uses the principle ofentanglement to facilitate communication that can absolutely detect whether a third party has intercepted a message in transit thus denying undetecteddecryption. By producing pairs of entangledphotons, QUESS will allow ground stations separated by many thousands of kilometres to establish securequantum channels.[3] QUESS itself has limited communication capabilities: it needsline-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]
The initial experiment demonstratedquantum key distribution (QKD) betweenXinjiang Astronomical Observatory nearÜrümqi andXinglong Observatory nearBeijing – agreat-circle distance of approximately 2,500 kilometres (1,600 mi).[3] In addition, QUESS testedBell's inequality at a distance of 1,200 km (750 mi) – further than any experiment to date – and teleported a photon state betweenShiquanhe Observatory inAli,Tibet Autonomous Region, and the satellite.[3] This requires very accurateorbital maneuvering and satellite tracking so the base stations can keep line-of-sight with the craft.[3][14] In 2021 full quantum state teleportation was demonstrated over 1,200 km (750 mi) at ground, based on entanglement distributed by the satellite.[15]
Once experiments within China concluded, QUESS created an international QKD channel between China and theInstitute 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]
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 aLong March 2D rocket fromJiuquan Launch Pad 603,Launch Area 4 on 17 August 2016, at 17:40 UTC (01:40 local time).[2]
The launch was a multi-payload mission shared with QUESS, LiXing-1 research satellite, and ³Cat-2 Spanish science satellite.
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 securecryptographic 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 randompolarization, with each party receiving one-half of the pair. This secret key can then be used as aone-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 usingfibre 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]
In addition, QUESS could test some of the basic foundations ofquantum mechanics.Bell's theorem says that nolocal hidden-variable theory can ever reproduce the predictions of quantum physics, and QUESS was able to test theprinciple of locality over 1,200 km (750 mi).[9][3]
The quantum key distribution experiment wonAmerican Association for the Advancement of Science (AAAS)'sNewcomb Cleveland Prize in 2018 for its contribution to laying the foundation for ultra-secure communication networks of the future.[17]
QUESS lead scientistPan Jianwei toldReuters that the project has "enormous prospects" in the defence sphere.[18] The satellite will provide secure communications between Beijing and Ürümqi, capital ofXinjiang, the remote western region of China.[18] TheUS Department of Defense believes China is aiming to achieve the capability to counter the use of enemy space technology.[18]Chinese Communist Partygeneral secretaryXi Jinping has prioritised China's space program, which has includedanti-satellite missile tests, and theNew York Times noted that quantum technology was a focus of thethirteenth five-year plan, which the China government set out earlier that year.[19] TheWall Street Journal said that the launch put China ahead of rivals, and brought them closer to "hack-proof communications".[20] Several outlets identifiedEdward Snowden'sleak of US surveillance documents as an impetus for the development of QUESS, withPopular Science calling it "a satellite for the post-Snowden age".[14][21][22]
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 acubesat by theNational University of Singapore and theUniversity of Strathclyde.[23] A German consortium has performed quantum measurements of optical signals from thegeostationaryAlphasatLaser 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 the late 2025 to early 2026,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]
