View source for Engineering:Quantum Experiments at Space Scale

{{Short description|Chinese quantum research satellite}}
{{Infobox spaceflight
| name                  = Quantum Experiments at Space Scale
| names_list            = Quantum Space Satellite<br />Micius / [[Biography:Mozi|Mozi]]
| image                 =
| image_caption         =
| image_alt             =
| image_size            = <!--include px/em; defaults to 220px-->
<!--mission insignia or patch-->
| insignia              =
| insignia_caption      = <!--image caption-->
| insignia_alt          =
| insignia_size         = <!--include px/em; defaults to 180px-->
| mission_type          = Technology demonstrator
| operator              = Chinese Academy of Sciences
| website               =
| COSPAR_ID             = 2016-051A<ref name="Gunter">{{cite web |url = http://space.skyrocket.de/doc_sdat/qss.htm |title = QSS (Mozi) |website=space.skyrocket.de |publisher=Gunter's Space Page |access-date=17 August 2016}}</ref>
| SATCAT                =
| mission_duration      = 2 years (planned)
<!--Spacecraft properties-->
| manufacturer          = Chinese Academy of Sciences
| dry_mass              =
| BOL_mass              = {{convert|631|kg|lb|abbr=on}}
| launch_mass           =
| payload_mass          =
| dimensions            =
| power                 = <!--end-of-life power, in watts-->
<!--Launch details-->
| launch_date           = 17:40 UTC, 16 August 2016<ref name="Spaceflights">{{cite web |url = http://spaceflights.news/?p=42332 |title = QUESS launched from the cosmodrome on Gobi desert |website = Spaceflights.news |date = 17 August 2016 |access-date = 17 August 2016 |archive-url = https://web.archive.org/web/20170617090336/http://spaceflights.news/?p=42332 |archive-date = 17 June 2017 |url-status = dead }}</ref>
| launch_rocket         = [[Engineering:Long March 2D|Long March 2D]]
| launch_site           = Jiuquan LA-4
| launch_contractor     = [[Organization:Shanghai Academy of Spaceflight Technology|Shanghai Academy of Spaceflight Technology]]
| entered_service       = <!--date on which the spacecraft entered service, if it did not do so immediately after launch-->
<!--orbit parameters-->
| orbit_epoch           =
| orbit_reference       =
| orbit_regime          = Sun-synchronous
| orbit_periapsis       = {{convert|488|km|mi|abbr=on}}<ref name="Spaceflights" />
| orbit_apoapsis        = {{convert|584|km|mi|abbr=on}}<ref name="Spaceflights" />
| orbit_inclination     = 97.4 degrees<ref name="Spaceflights" />
| apsis                 = gee
<!--end of mission-->
| disposal_type         = <!--Whether the spacecraft was deorbited, decommissioned, placed in a graveyard orbit, etc-->
| deactivated           = <!-- when craft was decommissioned -->
| last_contact          = <!-- when last signal received if not decommissioned -->
| instruments           = Sagnac interferometer
<!--transponder parameters-->
| trans_band            = [[Physics:Ultraviolet|Ultraviolet]]<ref name="IOP" />
| trans_frequency       = <!--specific frequencies-->
| trans_bandwidth       =
}}

'''Quantum Experiments at Space Scale''' ('''QUESS'''; {{zh |c = {{linktext|量子|科学|实验|卫星}} |p = Liàngzǐ kēxué shíyàn wèixīng|l=Quantum Science Experiment Satellite}}), is a Chinese research project in the field of quantum physics.

'''[[Engineering:Tiangong-2|Tiangong-2]]''' is China's second Space Laboratory module which was launched on 15 September 2016. [[Engineering:Tiangong-2|Tiangong-2]] carries a total of 14 mission<ref name="Tiangong2">{{cite web |title = Tiangong2 |url = https://chinaspacereport.com/spacecraft/tiangong2/ |website = chinaspacereport.com |publisher = China Space Report |access-date = 12 Nov 2017 |date = 28 April 2017 |archive-date = 17 May 2018 |archive-url = https://web.archive.org/web/20180517202146/https://chinaspacereport.com/spacecraft/tiangong2/ |url-status = dead }}</ref> and experiment packages, including Space-Earth [[Quantum key distribution|quantum key distribution]] ({{zh|c=量子密钥分发}}) and laser communications experiment to facilitate space-to-ground quantum communication.<ref name="chinaspacereport">{{cite news|url=https://chinaspacereport.com/spacecraft/tiangong2/|title=Tiangong-2 takes China one step closer to space station|author=huaxia|date=16 September 2016|access-date=12 November 2017|publisher=chinaspacereport|archive-date=17 May 2018|archive-url=https://web.archive.org/web/20180517202146/https://chinaspacereport.com/spacecraft/tiangong2/|url-status=dead}}</ref>

A satellite, nicknamed '''Micius''' or '''[[Biography:Mozi|Mozi]]''' ({{zh|c=墨子}}) after the ancient Chinese philosopher, is operated by the Chinese Academy of Sciences, as well as ground stations in China. The [[Organization:University of Vienna|University of Vienna]] and the Austrian Academy of Sciences are running the satellite's European receiving stations.<ref name="OeAW">{{cite web |url = http://www.oeaw.ac.at/en/events-communication/public-relations-communication/public-relations-communication/ausgewaehlte-oeaw-pressemeldungen/press-releases/first-quantum-satellite-successfully-launched/ |title = First Quantum Satellite Successfully Launched |date = 16 August 2016 |access-date = 17 August 2016 |website = Austrian Academy of Sciences |archive-date = 18 March 2018 |archive-url = https://web.archive.org/web/20180318054341/https://www.oeaw.ac.at/en/events-communication/public-relations-communication/public-relations-communication/ausgewaehlte-oeaw-pressemeldungen/press-releases/first-quantum-satellite-successfully-launched/ |url-status = dead }}</ref><ref name="Spacecom" />

QUESS is a proof-of-concept mission designed to facilitate [[Physics:Quantum optics|quantum optics]] experiments over long distances to allow the development of quantum encryption and [[Quantum teleportation|quantum teleportation]] technology.<ref>{{Cite journal |last1=Ren |first1=Ji-Gang |last2=Xu |first2=Ping |last3=Yong |first3=Hai-Lin |last4=Zhang |first4=Liang |last5=Liao |first5=Sheng-Kai |last6=Yin |first6=Juan |last7=Liu |first7=Wei-Yue |last8=Cai |first8=Wen-Qi |last9=Yang |first9=Meng |last10=Li |first10=Li |last11=Yang |first11=Kui-Xing |date=2017-08-09 |title=Ground-to-satellite quantum teleportation |journal=Nature |language=en |volume=549 |issue=7670 |pages=70–73 |doi=10.1038/nature23675 |pmid=28825708 |issn=1476-4687 |arxiv=1707.00934 |bibcode=2017Natur.549...70R |s2cid=4468803}}</ref><ref name="1200km-entanglement">{{cite journal |title=Satellite-based entanglement distribution over 1200 kilometers |author1=Juan Yin |author2=Yuan Cao |author3=Yu-Huai Li |author4=Sheng-Kai Liao |author5=Liang Zhang |author6=Ji-Gang Ren |author7=Wen-Qi Cai |author8=Wei-Yue Liu |author9=Bo Li |author10=Hui Dai |author11=Guang-Bing Li |author12=Qi-Ming Lu |author13=Yun-Hong Gong |author14=Yu Xu |author15=Shuang-Lin Li |author16=Feng-Zhi Li |author17=Ya-Yun Yin |author18=Zi-Qing Jiang |author19=Ming Li |author20=Jian-Jun Jia |author21=Ge Ren |author22=Dong He |author23=Yi-Lin Zhou |author24=Xiao-Xiang Zhang |author25=Na Wang |author26=Xiang Chang |author27=Zhen-Cai Zhu |author28=Nai-Le Liu |author29=Yu-Ao Chen |author30=Chao-Yang Lu |author31=Rong Shu |author32=Cheng-Zhi Peng |author33=Jian-Yu Wang |author34=Jian-Wei Pan |journal=Quantum Optics |year=2017 |volume=356 |issue=6343 |pages=1140–1144 |doi=10.1126/science.aan3211 |pmid=28619937 |arxiv=1707.01339 |s2cid=5206894}}</ref><ref>{{cite web |title=China Shatters "Spooky Action at a Distance" Record, Preps for Quantum Internet |first=Lee |last=Billings |website=Scientific American |url=https://www.scientificamerican.com/article/china-shatters-ldquo-spooky-action-at-a-distance-rdquo-record-preps-for-quantum-internet/}}</ref><ref>{{cite web |url=https://www.science.org/content/article/china-s-quantum-satellite-achieves-spooky-action-record-distance |title=China's quantum satellite achieves 'spooky action' at record distance |first1=Gabriel |last1=Popkin |date=15 June 2017 |website=Science - AAAS}}</ref><ref name="Spacecom">{{cite web |last1=Wall |first1=Mike |title=China Launches Pioneering 'Hack-Proof' Quantum-Communications Satellite |url=http://www.space.com/33760-china-launches-quantum-communications-satellite.html |website=Space.com |publisher=Purch |access-date=17 August 2016 |date=16 August 2016}}</ref> Quantum encryption uses the principle of [[Quantum entanglement|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 [[Physics:Photons|photons]], QUESS will allow ground stations separated by many thousands of kilometres to establish secure [[Quantum channel|quantum channel]]s.<ref name="IOP">{{cite news |url=https://physicsworld.com/a/china-launches-worlds-first-quantum-science-satellite/|title=China launches world's first quantum science satellite|author=Lin Xing |newspaper=Physics World|publisher=Institute of Physics |date=16 August 2016 |access-date=22 November 2020}}</ref> QUESS itself has limited communication capabilities: it needs [[Line-of-sight propagation|line-of-sight]], and can only operate when not in sunlight.<ref name="Xinhua">{{cite news |url=http://news.xinhuanet.com/english/2016-08/16/c_135604287.htm |access-date=17 August 2016 |archive-url=https://web.archive.org/web/20160817155904/http://news.xinhuanet.com/english/2016-08/16/c_135604287.htm |url-status=dead |archive-date=August 17, 2016 |title=China Focus: China's space satellites make quantum leap |author=huaxia|date=16 August 2016 |publisher=Xinhua}}</ref>

Further Micius satellites were planned, including a global network by 2030.<ref name="Xinhua" /><ref name="PopSci">{{cite news |url=http://www.popsci.com/chinas-quantum-satellite-could-change-cryptography-forever|title=China's Quantum Satellite Could Change Cryptography Forever|author1=Jeffrey Lin |author2=P.W. Singer |author3=John Costello |date=3 March 2016|access-date=17 August 2016 |newspaper=Popular Science}}</ref>

The mission cost was around US$100&nbsp;million in total.<ref name="Spaceflights" />

== Mission ==
{{Location map+ |Asia| float =
| caption = Ground stations
| places =
  {{Location map~ |Asia
    | label = Xinglong
    | position = top
    | marksize = 10
    | link = Beijing Astronomical Observatory#Xinglong
    | lat_deg = 40.39457
    | lon_deg = 117.577048
  }}
  {{Location map~ |Asia
    | label = Ürümqi
    | position = top
    | marksize = 10
    | link = Xinjiang Astronomical Observatory
    | lat_deg = 43.47
    | lon_deg = 87.18
  }}
  {{Location map~ |Asia
    | label = Ali
    | position = top
    | marksize = 10
    | link = Shiquanhe#Shiquanhe Observatory
    | lat_deg = 32.316667
    | lon_deg = 80.016667
  }}
  {{Location map~ |Asia
    | label = Vienna
    | position = top
    | marksize = 10
    | link = Institute for Quantum Optics and Quantum Information
    | lat_deg = 48.22    | lon_deg = 16.35
  }}
}}

The initial experiment demonstrated [[Quantum key distribution|quantum key distribution]] (QKD) between Xinjiang Astronomical Observatory near [[Place:Ürümqi|Ürümqi]] and Xinglong Observatory near [[Place:Beijing|Beijing]] – a [[Great-circle distance|great-circle distance]] of approximately {{convert|2500|km|mi}}.<ref name="IOP" /> In addition, QUESS tested Bell's inequality at a distance of {{convert|1200|km|mi|abbr=on}} – further than any experiment to date – and teleported a photon state between Shiquanhe Observatory in Ali, Tibet Autonomous Region, and the satellite.<ref name="IOP" /> This requires very accurate [[Astronomy:Orbital maneuver|orbital maneuver]]ing and satellite tracking so the base stations can keep line-of-sight with the craft.<ref name="IOP" /><ref name="AP">{{cite news |url = http://bigstory.ap.org/article/533a4f56ef664f8081a4bbb4aed00f79/chinas-launch-quantum-satellite-major-step-space-race |title = China's launch of quantum satellite major step in space race |date = 16 August 2016 |access-date = 17 August 2016 |publisher = Associated Press |archive-date = 27 October 2016 |archive-url = https://web.archive.org/web/20161027000232/http://bigstory.ap.org/article/533a4f56ef664f8081a4bbb4aed00f79/chinas-launch-quantum-satellite-major-step-space-race |url-status = dead }}</ref> In 2021 full quantum state teleportation was demonstrated over {{convert|1200|km|mi|abbr=on}} at ground, based on entanglement distributed by the satellite.<ref>{{Cite journal |last1=Li |first1=Bo |last2=Cao |first2=Yuan |last3=Li |first3=Yu-Huai |last4=Cai |first4=Wen-Qi |last5=Liu |first5=Wei-Yue |last6=Ren |first6=Ji-Gang |last7=Liao |first7=Sheng-Kai |last8=Wu |first8=Hui-Nan |last9=Li |first9=Shuang-Lin |last10=Li |first10=Li |last11=Liu |first11=Nai-Le |date=2022-04-26 |title=Quantum State Transfer over 1200 km Assisted by Prior Distributed Entanglement |url=https://link.aps.org/doi/10.1103/PhysRevLett.128.170501 |journal=Physical Review Letters |language=en |volume=128 |issue=17 |pages=170501 |doi=10.1103/PhysRevLett.128.170501 |pmid=35570417  |bibcode=2022PhRvL.128q0501L |s2cid=248812124 |issn=0031-9007|url-access=subscription }}</ref>

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 {{convert|7500|km|mi|abbr=on}}, enabling the first intercontinental secure quantum video call in 2016.<ref name="IOP" /><ref name="OeAW" />

=== 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.<ref name="Insider">{{cite news |url=http://www.spaceflightinsider.com/space-flight-news/china-launches-world-first-quantum-communications-satellite/ |title=China launches world's first quantum communications satellite into space |date=16 August 2016 |access-date=17 August 2016 |author=Tomasz Nowakowski |publisher=Spaceflight Insider}}</ref> The spacecraft was launched by a [[Engineering:Long March 2D|Long March 2D]] rocket from Jiuquan Launch Pad 603, Launch Area 4 on 17 August 2016, at 17:40 UTC (01:40 local time).<ref name="Spaceflights" />

=== 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&nbsp;km. Its mass is 110&nbsp;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 [[Engineering:CubeSat|CubeSat]] flying a novel [[Earth:Satellite navigation|GNSS]] Reflectometer (GNSS-R) payload for Earth observation. Its mass is 7.1 kg.

== Secure key distribution ==
{{main|Quantum key distribution}}
The main instrument on board QUESS is a "[[Physics:Sagnac effect|Sagnac effect]]" interferometer.<ref name="IOP" /> This is a device which 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 [[Key (cryptography)|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 [[Physics:Polarization (waves)|polarization]], with each party receiving one half of the pair. This secret key can then be used as a [[One-time pad|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.<ref name="PopSci" /> 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, fibre 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.<ref name="IOP" />

In addition, QUESS could tests some of the basic foundations of [[Physics:Quantum mechanics|quantum mechanics]]. [[Bell's theorem]] says that no [[Local hidden-variable theory|local hidden-variable theory]] can ever reproduce the predictions of quantum physics, and QUESS was able to test the [[Physics:Principle of locality|principle of locality]] over {{convert|1200|km|mi|abbr=on}}.<ref name="1200km-entanglement" /><ref name="IOP" />

== Analysis ==
QUESS lead scientist [[Biography:Pan Jianwei|Pan Jianwei]] told ''{{wipe|Reuters}}'' that the project has "enormous prospects" in the defence sphere.<ref name=R>{{cite news |url=http://uk.reuters.com/article/uk-china-space-satellite-idUKKCN10R073 |title=China launches 'hack-proof' communications satellite |work={{wipe|Reuters}} |date=2016-08-16 |access-date=2016-08-18 }}</ref> The satellite will provide secure communications between Beijing and Ürümqi, capital of [[Place:Xinjiang|Xinjiang]], the remote western region of China.<ref name=R /> The US Department of Defense believes China is aiming to achieve the capability to counter the use of enemy space technology.<ref name=R /> Chinese Communist Party general secretary [[Biography:Xi Jinping|Xi Jinping]] has prioritised China's space program, which has included anti-satellite missile tests, and the ''{{wipe|New York Times}}'' noted that quantum technology was a focus of the thirteenth five-year plan, which the China government set out earlier that year.<ref name="NYT">{{cite news|url=https://www.nytimes.com/2016/08/17/world/asia/china-quantum-satellite-mozi.html?_r=0|title=China Launches Quantum Satellite in Bid to Pioneer Secure Communications|author=Edward Wong|date=16 August 2016|access-date=19 August 2016|newspaper=New York Times}}</ref> The ''Wall Street Journal'' said that the launch put China ahead of rivals, and brought them closer to "hack-proof communications".<ref name="WSJ">{{cite news|url=https://www.wsj.com/articles/chinas-latest-leap-forward-isnt-just-greatits-quantum-1471269555?mod=rss_Technology|title=China's Latest Leap Forward Isn't Just Great—It's Quantum|author=Josh Chin|date=16 August 2016|access-date=19 August 2016|newspaper=Wall Street Journal}}</ref> Several outlets identified Edward Snowden's leak of US surveillance documents as an impetus for the development of QUESS, with ''Popular Science'' calling it "a satellite for the post-Snowden age".<ref name="AP" /><ref name="Popsci2">{{cite news|url=http://www.popsci.com/china-launches-quantum-satellite-in-search-for-unhackable-communications|title=China Launches Quantum Satellite In Search Of Unhackable Communications|author1=Jeffrey Lin  |author2=P.W. Singer|date=17 August 2016|access-date=19 August 2016}}</ref><ref name="FT">{{cite news|url=http://www.ft.com/cms/s/0/f333dbea-6371-11e6-a08a-c7ac04ef00aa.html#axzz4Hm0TcdSW|title=China launches quantum satellite in battle against hackers|author=Lucy Hornby, Clive Cookson|date=16 August 2016|access-date=19 August 2016}}</ref>

== Similar projects ==
QUESS is the first spacecraft launched capable of generating entangled photons in space,<ref name="Spacecom" /> although transmission of single photons via satellites has previously been demonstrated by reflecting photons generated at ground-based stations off orbiting satellites.<ref name="Nature">{{cite journal|title=Chinese satellite is one giant step for the quantum internet|date=27 July 2016|pages=478–479|doi=10.1038/535478a|journal=Nature|author=Elizabeth Gibney|volume=535|issue=7613|pmid=27466107|bibcode=2016Natur.535..478G|doi-access=free}}</ref> While not generating fully entangled photons, [[Physics:Quantum correlation|correlated]] pairs of photons have been produced in space using a cubesat by the National University of Singapore and the [[Organization:University of Strathclyde|University of Strathclyde]].<ref name="Nature" /> A German consortium has performed quantum measurements of optical signals from the [[Astronomy:Geostationary orbit|geostationary]] Alphasat [[Engineering:Laser communication in space|Laser Communication Terminal]].<ref>{{Cite journal |arxiv=1608.03511|last1=Günthner|first1=Kevin|title=Quantum-limited measurements of optical signals from a geostationary satellite|last2=Khan|first2=Imran|last3=Elser|first3=Dominique|last4=Stiller|first4=Birgit|last5=Bayraktar|first5=Ömer|last6=Müller|first6=Christian R|last7=Saucke|first7=Karen|last8=Tröndle|first8=Daniel|last9=Heine|first9=Frank|last10=Seel|first10=Stefan|last11=Greulich|first11=Peter|last12=Zech|first12=Herwig|last13=Gütlich|first13=Björn|last14=Philipp-May|first14=Sabine|last15=Marquardt|first15=Christoph|last16=Leuchs|first16=Gerd|journal=Optica|year=2017|volume=4|issue=6|pages=611–616|doi=10.1364/OPTICA.4.000611|bibcode=2017Optic...4..611G|s2cid=15100033}}</ref> 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, [[Organization:European Space Agency|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).<ref>{{cite web|url=https://www.esa.int/Applications/Telecommunications_Integrated_Applications/Quantum_encryption_to_boost_European_autonomy|title=Quantum encryption to boost European autonomy|publisher=[[Organization:European Space Agency|ESA]]|date=22 September 2022}}</ref>

== See also ==
* Chinese space program
* [[Quantum information science]]
* [[Quantum information]]
** [[Quantum cryptography]]
** [[Quantum computing]]
** [[Quantum key distribution]]
** [[Quantum teleportation]]

== References ==
{{Reflist|30em}}

== External links ==
* [http://www.chinaspaceflight.com/satellite/Space-Science/QUESS/QUESS-launch.html QUESS Launching] {{Webarchive|url=https://web.archive.org/web/20171106155940/http://www.chinaspaceflight.com/satellite/Space-Science/QUESS/QUESS-launch.html |date=2017-11-06 }}(Chinese)
* [http://nanosatlab.upc.edu/en/missions-and-projects/3cat-2 3Cat-2 Satellite web site] at Polytechnic University of Catalonia


[[Category:Communications satellites]]
[[Category:Quantum information science]]

{{Sourceattribution|Quantum Experiments at Space Scale}}