Editing Quantum key distribution (section)

== Implementations ==

=== Experimental ===
In 1991, [[John Rarity]], [[Paul Tapster]] and [[Artur Ekert]], researchers from the UK Defence Research Agency in Malvern and Oxford University, demonstrated quantum key distribution protected by the violation of the Bell inequalities.

In 2008, exchange of secure keys at 1&nbsp;Mbit/s (over 20&nbsp;km of optical fibre) and 10&nbsp;kbit/s (over 100&nbsp;km of fibre), was achieved by a collaboration between the [[University of Cambridge]] and [[Toshiba]] using the BB84 protocol with [[decoy state]] pulses.<ref>{{Cite journal |arxiv = 0810.1069|last1 = Dixon|first1 = A.R.|title = Gigahertz decoy quantum key distribution with 1 Mbit/s secure key rate|journal = Optics Express|volume = 16|issue = 23|pages = 18790–7|author2 = Z.L. Yuan|last3 = Dynes|first3 = J.F.|last4 = Sharpe|first4 = A. W.|last5 = Shields|first5 = A. J.|year = 2008|doi = 10.1364/OE.16.018790|pmid = 19581967|bibcode = 2008OExpr..1618790D|s2cid = 17141431}}</ref>

In 2007, [[Los Alamos National Laboratory]]/[[NIST]] achieved quantum key distribution over a 148.7&nbsp;km of optic fibre using the BB84 protocol.<ref>{{cite journal | last1=Hiskett | first1=P A | last2=Rosenberg | first2=D | last3=Peterson | first3=C G | last4=Hughes | first4=R J | last5=Nam | first5=S | last6=Lita | first6=A E | last7=Miller | first7=A J | last8=Nordholt | first8=J E |author8-link=Beth Nordholt| title=Long-distance quantum key distribution in optical fibre | journal=New Journal of Physics | publisher=IOP Publishing | volume=8 | issue=9 | date=2006-09-14 | issn=1367-2630 | doi=10.1088/1367-2630/8/9/193 | pages=193|doi-access=free| bibcode=2006NJPh....8..193H | arxiv=quant-ph/0607177 }}</ref> Significantly, this distance is long enough for almost all the spans found in today's fibre networks. A European collaboration achieved free space QKD over 144&nbsp;km between two of the [[Canary Islands]] using entangled photons (the Ekert scheme) in 2006,<ref>{{Cite journal |arxiv = quant-ph/0607182|last1 = Ursin|first1 = Rupert|title = Entanglement-based quantum communication over 144 km &nbsp;km|journal = Nature Physics|volume = 3|issue = 7|pages = 481–486|first2 = Felix|last2 = Tiefenbacher|last3 = Schmitt-Manderbach|first3 = T.|last4 = Weier|first4 = H.|last5 = Scheidl|first5 = T.|last6 = Lindenthal|first6 = M.|last7 = Blauensteiner|first7 = B.|last8 = Jennewein|first8 = T.|last9 = Perdigues|first9 = J.|last10 = Trojek|first10 = P.|last11 = Ömer|first11 = B.|last12 = Fürst|first12 = M.|last13 = Meyenburg|first13 = M.|last14 = Rarity|first14 = J.|last15 = Sodnik|first15 = Z.|last16 = Barbieri|first16 = C.|last17 = Weinfurter|first17 = H.|last18 = Zeilinger|first18 = A.|year = 2006|doi = 10.1038/nphys629|bibcode = 2006quant.ph..7182U| s2cid=108284907 }}</ref> and using BB84 enhanced with [[decoy states]]<ref name="HwangDecoy">{{cite journal | last=Hwang | first=Won-Young | title=Quantum Key Distribution with High Loss: Toward Global Secure Communication | journal=Physical Review Letters | volume=91 | issue=5 | date=2003-08-01 | issn=0031-9007 | doi=10.1103/physrevlett.91.057901 | pmid=12906634 | page=057901| arxiv=quant-ph/0211153 | bibcode=2003PhRvL..91e7901H | s2cid=19225674 }}</ref><ref name="VWDecoy">H.-K. Lo, in Proceedings of 2004 IEEE ISIT (IEEE Press, New York, 2004), p. 137</ref><ref name="wangDecoy">{{cite journal | last=Wang | first=Xiang-Bin | title=Beating the Photon-Number-Splitting Attack in Practical Quantum Cryptography | journal=Physical Review Letters | volume=94 | issue=23 | date=2005-06-16 | issn=0031-9007 | doi=10.1103/physrevlett.94.230503 | pmid=16090451 | page=230503|arxiv=quant-ph/0410075| bibcode=2005PhRvL..94w0503W | s2cid=2651690 }}</ref><ref name="LoDecoy">H.-K. Lo, X. Ma, K. Chen, [https://archive.today/20120712103031/http://prl.aps.org/abstract/PRL/v94/i23/e230504 "Decoy State Quantum Key Distribution"], Physical Review Letters, 94, 230504 (2005)</ref><ref name="PracticalDecoy">{{Cite journal | doi=10.1103/PhysRevA.72.012326|title = Practical decoy state for quantum key distribution| journal=Physical Review A| volume=72|issue = 1|pages = 012326|year = 2005|last1 = Ma|first1 = Xiongfeng| last2=Qi| first2=Bing| last3=Zhao| first3=Yi| last4=Lo| first4=Hoi-Kwong| arxiv=quant-ph/0503005|bibcode = 2005PhRvA..72a2326M|s2cid = 836096}}</ref> in 2007.<ref>{{cite journal | last1=Schmitt-Manderbach | first1=Tobias | last2=Weier | first2=Henning | last3=Fürst | first3=Martin | last4=Ursin | first4=Rupert | last5=Tiefenbacher | first5=Felix | last6=Scheidl | first6=Thomas | last7=Perdigues | first7=Josep | last8=Sodnik | first8=Zoran | last9=Kurtsiefer | first9=Christian | last10=Rarity | first10=John G. | last11=Zeilinger | first11=Anton | last12=Weinfurter | first12=Harald |display-authors=5| title=Experimental Demonstration of Free-Space Decoy-State Quantum Key Distribution over 144&nbsp;km | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=98 | issue=1 | date=2007-01-05 | issn=0031-9007 | doi=10.1103/physrevlett.98.010504 | pmid=17358463 | page=010504|url=http://xqp.physik.lmu.de/publications/files/articles_2007/prl_98_010504.pdf| bibcode=2007PhRvL..98a0504S | s2cid=15102161 }}</ref>

{{As of|2015|8}} the longest distance for optical fiber (307&nbsp;km)<ref name="Korzh14">
{{cite journal
|last1=Korzh
|first1=Boris
|last2=Lim
|first2=Charles Ci Wen
|last3=Houlmann
|first3=Raphael
|last4=Gisin
|first4=Nicolas
|last5=Li
|first5=Ming Jun
|last6=Nolan
|first6=Daniel
|last7=Sanguinetti
|first7=Bruno
|last8=Thew
|first8=Rob
|last9=Zbinden
|first9=Hugo
|arxiv=1407.7427
|title=Provably Secure and Practical Quantum Key Distribution over 307&nbsp;km of Optical Fibre
|year=2015
|doi=10.1038/nphoton.2014.327
|volume=9
|issue=3
|journal=Nature Photonics
|pages=163–168
|bibcode=2015NaPho...9..163K
|s2cid=59028718
}}
</ref> was achieved by [[University of Geneva]] and [[Corning Inc.]] In the same experiment, a secret key rate of 12.7&nbsp;kbit/s was generated, making it the highest bit rate system over distances of 100&nbsp;km. In 2016 a team from Corning and various institutions in China achieved a distance of 404&nbsp;km, but at a bit rate too slow to be practical.<ref>{{cite journal
|title=Satellite-based entanglement distribution over 1200 kilometers
| volume=356
| doi=10.1126/science.aan3211
| pmid=28619937
| number=6343
| journal=Science
| last1=Yin
| first1=Juan
|last2=Cao
|first2= Yuan 
|last3= Li
|first3= Yu-Huai
|last4= Liao
|first4= Sheng-Kai
|last5= Zhang
|first5= Liang
|last6= Ren
|first6= Ji-Gang 
|last7= Cai
|first7= Wen-Qi
|last8=Liu
|first8= Wei-Yue
|last9= Li
|first9= Bo 
|last10= Dai
|first10=Hui
|display-authors=etal
| year=2017
| pages=1140–1144| arxiv=1707.01339
| bibcode=2017arXiv170701339Y
| s2cid=5206894
}}</ref>

In June 2017, physicists led by [[Thomas Jennewein]] at the [[Institute for Quantum Computing]] and the [[University of Waterloo]] in [[Waterloo, Ontario|Waterloo, Canada]] achieved the first demonstration of quantum key distribution from a ground transmitter to a moving aircraft. They reported optical links with distances between 3–10&nbsp;km and generated secure keys up to 868 kilobytes in length.<ref>{{cite journal | last1 = Pugh | first1 = C. J. | last2 = Kaiser | first2 = S. | last3 = Bourgoin | first3 = J.- P. | last4 = Jin | first4 = J. | last5 = Sultana | first5 = N. | last6 = Agne | first6 = S. | last7 = Anisimova | first7 = E. | last8 = Makarov | first8 = V. | last9 = Choi | first9 = E. | last10 = Higgins | first10 = B. L. | last11 = Jennewein | first11 = T. | year = 2017 | title = Airborne demonstration of a quantum key distribution receiver payload | journal = Quantum Science and Technology | volume = 2 | issue = 2| page = 024009 | doi = 10.1088/2058-9565/aa701f | arxiv = 1612.06396 | bibcode = 2017QS&T....2b4009P | s2cid = 21279135 }}</ref>

Also in June 2017, as part of the [[Quantum Experiments at Space Scale]] project, Chinese physicists led by [[Pan Jianwei]] at the [[University of Science and Technology of China]] measured entangled photons over a distance of 1203&nbsp;km between two ground stations, laying the groundwork for future intercontinental quantum key distribution experiments.<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 a record distance |date=2017-06-15 |access-date=2017-06-15}}</ref> Photons were sent from one ground station to the satellite they had named ''[[Micius (satellite)|Micius]]'' and back down to another ground station, where they "observed a survival of two-photon entanglement and a violation of Bell inequality by 2.37 ± 0.09 under strict Einstein locality conditions" along a "summed length varying from 1600 to 2400 kilometers."<ref>{{cite journal | last1 = Yin | first1 = J. | author-link33 = J.- W. Pan | last2 = Cao | first2 = Y. | last3 = Li | first3 = Y.- H. | last4 = Liao | first4 = S.- K. | last5 = Zhang | first5 = L. | last6 = Ren | first6 = J.- G. | last7 = Cai | first7 = W.- Q. | last8 = Liu | first8 = W.- Y. | last9 = Li | first9 = B. | last10 = Dai | first10 = H. | last11 = Li | first11 = G.- B. | last12 = Lu | first12 = Q.- M. | last13 = Gong | first13 = Y.- H. | last14 = Xu | first14 = Y. | last15 = Li | first15 = S.- L. | last16 = Li | first16 = F.- Z. | last17 = Yin | first17 = Y.- Y. | last18 = Jiang | first18 = Z.- Q. | last19 = Li | first19 = M. | last20 = Jia | first20 = J.- J. | last21 = Ren | first21 = G. | last22 = He | first22 = D. | last23 = Zhou | first23 = Y.- L. | last24 = Zhang | first24 = X.- X. | last25 = Wang | first25 = N. | last26 = Chang | first26 = X. | last27 = Zhu | first27 = Z.- C. | last28 = Liu | first28 = N.- L. | last29 = Lu | first29 = C.- Y. | last30 = Shu | first30 = R. | last31 = Peng | first31 = C.- Z. | last32 = Wang | first32 = J.- Y. | last33 = Pan | first33 = J.- W. | year = 2017| title = Satellite-based entanglement distribution over 1200 kilometers | journal = Science | volume = 356 | issue = 6343| pages = 1140–4 | doi = 10.1126/science.aan3211 | pmid = 28619937 | arxiv = 1707.01339 | doi-access = free }}</ref> Later that year BB84 was successfully implemented over satellite links from ''Micius'' to ground stations in China and Austria. The keys were combined and the result was used to transmit images and video between Beijing, China, and Vienna, Austria.<ref>
{{cite journal
|  title = Satellite-Relayed Intercontinental Quantum Network
|  volume = 120
|  doi = 10.1103/PhysRevLett.120.030501
|  pmid = 29400544
|  number =3 
|  journal =	Physical Review Letters
|  last1 =Liao
|first1 = Sheng-Kai
|last2= Cai
|first2= Wen-Qi
|last3= Handsteiner|
first3 =   Johannes|
last4= Liu|
first4= Bo |
last5 =Yin|
first5= Juan|
last6= Zhang|
first6= Liang|
last7= Rauch|
first7= Dominik |
last8 = Fink|
first8= Matthias |
last9 = Ren|
first9= Ji-Gang |
last10= Liu|
first10= Wei-Yue
|display-authors=etal|
  year =2018|
  pages =030501
|arxiv=1801.04418|bibcode=2018PhRvL.120c0501L| s2cid = 206306725
}}</ref>

In August 2017, a group at Shanghai Jiaotong University experimentally demonstrate that polarization quantum states including general qubits of single photon and entangled states can survive well after travelling through seawater,<ref>{{Cite journal |doi=10.1364/OE.25.019795 |title=Towards quantum communications in free-space seawater |year=2017 |last1=Ji |first1=Ling |last2=Gao |first2=Jun |last3=Yang |first3=Ai-Lin |last4=Feng |first4=Zhen |last5=Lin |first5=Xiao-Feng |last6=Li |first6=Zhong-Gen |last7=Jin |first7=Xian-Min |journal=Optics Express |volume=25 |issue=17 |pages=19795–19806 |pmid=29041667 |s2cid=46757097 |arxiv=1602.05047 |bibcode=2017OExpr..2519795J }}</ref> representing the first step towards underwater quantum communication.

In May 2019 a group led by Hong Guo at Peking University and Beijing University of Posts and Telecommunications reported field tests of a continuous-variable QKD system through commercial fiber networks in Xi'an and Guangzhou over distances of 30.02&nbsp;km (12.48&nbsp;dB) and 49.85&nbsp;km (11.62&nbsp;dB) respectively.<ref>{{cite journal|last1=Zhang|first1=Yichen|last2=Li|first2=Zhengyu|last3=Chen|first3=Ziyang|last4=Weedbrook|first4=Christian|last5=Zhao|first5=Yijia|last6=Wang|first6=Xiangyu|last7=Huang|first7=Yundi|last8=Xu|first8=Chunchao|last9=Zhang|first9=Xiaoxiong|last10=Wang|first10=Zhenya|last11=Li|first11=Mei|last12=Zhang|first12=Xueying|last13=Zheng|first13=Ziyong|last14=Chu|first14=Binjie|last15=Gao|first15=Xinyu|last16=Meng|first16=Nan|last17=Cai|first17=Weiwen|last18=Wang|first18=Zheng|last19=Wang|first19=Gan|last20=Yu|first20=Song|last21=Guo|first21=Hong|title=Continuous-variable QKD over 50&nbsp;km commercial fiber|journal=Quantum Science and Technology|date=2019|volume=4|issue=3|pages= 035006|doi=10.1088/2058-9565/ab19d1|arxiv=1709.04618|bibcode=2019QS&T....4c5006Z|s2cid=116403328}}</ref>

In December 2020, Indian [[Defence Research and Development Organisation]] tested a QKD between two of its laboratories in Hyderabad facility. The setup also demonstrated the validation of detection of a third party trying to gain knowledge of the communication. Quantum based security against eavesdropping was validated for the deployed system at over {{cvt|12|km}} range and 10&nbsp;dB attenuation over fibre optic channel. A [[continuous wave]] laser source was used to generate photons without depolarization effect and timing accuracy employed in the setup was of the order of picoseconds. The [[Single-photon avalanche diode|Single photon avalanche detector]] (SPAD) recorded arrival of photons and key rate was achieved in the range of kbps with low Quantum bit error rate.<ref>{{Cite news|last=Ministry of Defence|date=2020-12-09|title=Quantum Communication between two DRDO Laboratories|url=https://pib.gov.in/PressReleasePage.aspx?PRID=1679349|work=Press Information Bureau|access-date=2021-03-22}}</ref>

In March 2021, [[Indian Space Research Organisation]] also demonstrated a free-space Quantum Communication over a distance of 300 meters. A free-space QKD was demonstrated at [[Space Applications Centre]] (SAC), Ahmedabad, between two line-of-sight buildings within the campus for video conferencing by quantum-key encrypted signals. The experiment utilised a [[NAVIC]] receiver for time synchronization between the transmitter and receiver modules. Later in January 2022, Indian scientists were able to successfully create an atmospheric channel for exchange of crypted messages and images. After demonstrating quantum communication between two ground stations, India has plans to develop Satellite Based Quantum Communication (SBQC).<ref>{{Cite news|date=2021-03-22|title=ISRO makes breakthrough demonstration of free-space Quantum Key Distribution (QKD) over 300 m|url=https://www.isro.gov.in/update/22-mar-2021/isro-makes-breakthrough-demonstration-of-free-space-quantum-key-distribution-qkd|work=Indian Space Research Organisation|access-date=2021-03-22|archive-date=22 March 2021|archive-url=https://web.archive.org/web/20210322164134/https://www.isro.gov.in/update/22-mar-2021/isro-makes-breakthrough-demonstration-of-free-space-quantum-key-distribution-qkd|url-status=dead}}</ref><ref>{{Cite news|date=2022-01-31|title=Department of Space demonstrates entanglement based quantum communication over 300m free space along with real time cryptographic applications|url=https://www.isro.gov.in/update/31-jan-2022/department-of-space-demonstrates-entanglement-based-quantum-communication-over|work=Indian Space Research Organisation|access-date=2022-02-01|archive-date=1 February 2022|archive-url=https://web.archive.org/web/20220201151914/https://www.isro.gov.in/update/31-jan-2022/department-of-space-demonstrates-entanglement-based-quantum-communication-over|url-status=dead}}</ref>

In July 2022, researchers published their work experimentally implementing a device-independent quantum key distribution (DIQKD) protocol that uses quantum entanglement (as suggested by Ekert)<ref name=":0" /> to insure resistance to quantum hacking attacks.<ref name=":1" /> They were able to create two ions, about two meters apart that were in a high quality entangled state using the following process: Alice and Bob each have ion trap nodes with an <sup>88</sup>Sr<sup>+</sup> qubit inside. Initially, they excite the ions to an electronic state, which creates an entangled state. This process also creates two photons, which are then captured and transported using an optical fiber, at which point a Bell-basis measurement is performed and the ions are projected to a highly entangled state. Finally the qubits are returned to new locations in the ion traps disconnected from the optical link so that no information can be leaked. This is repeated many times before the key distribution proceeds.<ref name=":1" />

A separate experiment published in July 2022 demonstrated implementation of DIQKD that also uses a Bell inequality test to ensure that the quantum device is functioning, this time at a much larger distance of about 400m, using an optical fiber 700m long.<ref name=":2" /> The set up for the experiment was similar to the one in the paragraph above, with some key differences. Entanglement was generated in a quantum network link (QNL) between two <sup>87</sup>Rb atoms in separate laboratories located 400m apart, connected by the 700m channel. The atoms are entangled by electronic excitation, at which point two photons are generated and collected, to be sent to the bell state measurement (BSM) setup. The photons are projected onto a |ψ<sup>+</sup> state, indicating maximum entanglement. The rest of the key exchange protocol used is similar to the original QKD protocol, with the only difference being that keys are generated with two measurement settings instead of one.<ref name=":2" />

Since the proposal of Twin Field Quantum Key Distribution in 2018, a myriad of experiments have been performed with the goal of increasing the distance in a QKD system. The most successful of which was able to distribute key information across a distance of 833.8&nbsp;km.<ref name=":5" />

In 2023, scientists at Indian Institute of Technology (IIT) Delhi have achieved a trusted-node-free quantum key distribution (QKD) up to ''380 km'' in standard telecom fiber with a very low quantum bit error rate (QBER).<ref>{{Cite web|url=https://www.educationtimes.com/article/campus-beat-college-life/99733828/emerging-technologies-iit-delhi-researchers-achieve-secure-quantum-communication-for-380-km-in-standard-telecom-fiber|title=EMERGING TECHNOLOGIES: IIT Delhi researchers achieve secure quantum communication for 380 km in standard telecom fiber - EducationTimes.com|website=www.educationtimes.com}}</ref>

In 2024 scientists in South Africa and China achieved quantum key distribution in the atmosphere with a record breaking distance of 12,900&nbsp;km,  using lasers and a [[Microsatellite (spaceflight)|microsatellite]] in [[low Earth orbit]]. They transferred over a million quantum-secure bits between South Africa and China during one orbit of the satellite.<ref>{{Cite journal |last=Li |first=Yang |last2=Cai |first2=Wen-Qi |last3=Ren |first3=Ji-Gang |last4=Wang |first4=Chao-Ze |last5=Yang |first5=Meng |last6=Zhang |first6=Liang |last7=Wu |first7=Hui-Ying |last8=Chang |first8=Liang |last9=Wu |first9=Jin-Cai |last10=Jin |first10=Biao |last11=Xue |first11=Hua-Jian |last12=Li |first12=Xue-Jiao |last13=Liu |first13=Hui |last14=Yu |first14=Guang-Wen |last15=Tao |first15=Xue-Ying |date=2025-03-19 |title=Microsatellite-based real-time quantum key distribution |url=https://www.nature.com/articles/s41586-025-08739-z |journal=Nature |language=en |pages=1–8 |doi=10.1038/s41586-025-08739-z |issn=1476-4687}}</ref>

=== Commercial ===

Many companies around the world offer commercial quantum key distribution, for example: [[ID Quantique]] (Geneva), [[Toshiba]],<ref>{{cite web | url=https://www.toshiba.eu/quantum/products/quantum-key-distribution/ | title=Quantum Key Distribution - What is QKD? How Does It Work? }}</ref> [[MagiQ Technologies, Inc.]] (New York), QNu Labs ([[Bengaluru]], [[India]]), [[QuintessenceLabs]] (Australia), [[QRate]] (Russia), SeQureNet (Paris), Quantum Optics Jena (Germany) and [https://www.keequant.com KEEQuant] (Germany). Several other companies also have active research programs, including [[KETS Quantum Security]] (UK), [[Hewlett-Packard|HP]], [[IBM]], [[Mitsubishi]], [[NEC]] and [[Nippon Telegraph and Telephone|NTT]] (See [[#External links|External links]] for direct research links).

In 2004, the world's first bank transfer using quantum key distribution was carried out in [[Vienna]], [[Austria]].<ref>http://www.secoqc.net/downloads/pressrelease/Banktransfer_english.pdf {{webarchive |url=https://web.archive.org/web/20130309095431/http://www.secoqc.net/downloads/pressrelease/Banktransfer_english.pdf |date=9 March 2013 }} ''secoqc.net''</ref> Quantum encryption technology provided by the Swiss company [[Id Quantique]] was used in the Swiss canton (state) of Geneva to transmit ballot results to the capital in the national election occurring on 21 October 2007.<ref>{{cite web|url=http://www.technewsworld.com/story/59793.html|title=Swiss Call New Vote Encryption System 'Unbreakable'|last=Jordans|first=Frank|date=12 October 2007|publisher=technewsworld.com|access-date=8 March 2013|archive-url=https://web.archive.org/web/20071209214958/http://www.technewsworld.com/story/59793.html |archive-date=2007-12-09}}</ref> In 2013, [[Battelle Memorial Institute]] installed a QKD system built by ID Quantique between their main campus in Columbus, Ohio and their manufacturing facility in nearby Dublin.<ref>{{cite web|url=http://tech.fortune.cnn.com/2013/10/14/quantum-key/|title=Unbreakable encryption comes to the U.S|last=Dillow|first=Clay|date=14 October 2013|publisher=fortune.cnn.com|url-status=dead|archive-url=https://web.archive.org/web/20131014104149/http://tech.fortune.cnn.com/2013/10/14/quantum-key/|archive-date=14 October 2013}}</ref> Field tests of Tokyo QKD network have been underway for some time.<ref>{{cite journal | last1 = Sasaki | first1 = M. | display-authors = etal | title = Field test of quantum key distribution in the Tokyo QKD Network | journal = Optics Express | year = 2011 | volume = 19 | issue = 11| pages = 10387–10409 | doi = 10.1364/OE.19.010387 | pmid = 21643295 | arxiv = 1103.3566 | bibcode = 2011OExpr..1910387S | s2cid = 593516 }}</ref>

=== Quantum key distribution networks ===

==== DARPA ====
The [[DARPA Quantum Network]],<ref>{{cite web|url=https://www.newscientist.com/article/dn7484|title=Quantum cryptography network gets wireless link|first=Will|last=Knight|access-date=18 August 2016}}</ref> was a 10-node quantum key distribution network, which ran continuously for four years, 24 hours a day, from 2004 to 2007 in Massachusetts in the United States. It was developed by [[BBN Technologies]], [[Harvard University]], [[Boston University]], with collaboration from [[IBM Research]], the [[National Institute of Standards and Technology]], and [[QinetiQ]]. It supported a standards-based Internet [[computer network]] protected by quantum key distribution.

==== SECOQC ====
{{main|Secure Communication based on Quantum Cryptography}}
The world's first [[computer network]] protected by quantum key distribution was implemented in October 2008, at a scientific conference in Vienna. The name of this network is [[Secure Communication based on Quantum Cryptography|SECOQC]] ('''Se'''cure '''Co'''mmunication Based on '''Q'''uantum '''C'''ryptography) and the [[European Union|EU]] funded this project. The network used 200&nbsp;km of standard [[fibre-optic cable]] to interconnect six locations across Vienna and the town of [[St Poelten]] located 69&nbsp;km to the west.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/sci/tech/7661311.stm|title='Unbreakable' encryption unveiled|date=9 October 2008|access-date=18 August 2016|via=bbc.co.uk}}</ref>

==== SwissQuantum ====
Id Quantique has successfully completed the longest running project for testing Quantum Key Distribution (QKD) in a field environment. The main goal of the SwissQuantum network project installed in the Geneva metropolitan area in March 2009, was to validate the reliability and robustness of QKD in continuous operation over a long time period in a field environment. The quantum layer operated for nearly 2 years until the project was shut down in January 2011 shortly after the initially planned duration of the test.

==== Chinese networks ====
In May 2009, a hierarchical quantum network was demonstrated in [[Wuhu]], [[China]]. The hierarchical network consisted of a backbone network of four nodes connecting a number of subnets. The backbone nodes were connected through an optical switching quantum router. Nodes within each subnet were also connected through an optical switch, which were connected to the backbone network through a trusted relay.<ref>{{citation
| title=Field experiment on a robust hierarchical metropolitan quantum cryptography network
| first1=FangXing  | last1=Xu
| first2=Wei       | last2=Chen
| first3=Shuang    | last3=Wang
| first4=ZhenQiang | last4=Yin
| first5=Yang      | last5=Zhang
| first6=Yun       | last6=Liu
| first7=Zheng     | last7=Zhou
| first8=YiBo      | last8=Zhao
| first9=HongWei   | last9=Li
| first10=Dong     | last10=Liu
| journal=Chinese Science Bulletin
| volume=54
| issue=17
| pages=2991–2997
| date=2009
| doi=10.1007/s11434-009-0526-3
| bibcode=2009ChSBu..54.2991X  | arxiv=0906.3576| s2cid=118300112 }}</ref>

Launched in August 2016, the [[Quantum Experiments at Space Scale|QUESS]] space mission created an international QKD channel between China and the [[Institute for Quantum Optics and Quantum Information]] in [[Vienna]], [[Austria]] − a ground distance of {{convert|7500|km|mi|abbr=on}}, enabling the first intercontinental secure quantum video call.<ref name="IOP">{{cite news|url=http://physicsworld.com/cws/article/news/2016/aug/16/china-launches-world-s-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=17 August 2016|archive-date=1 December 2017|archive-url=https://web.archive.org/web/20171201030546/http://physicsworld.com/cws/article/news/2016/aug/16/china-launches-world-s-first-quantum-science-satellite|url-status=dead}}</ref><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">{{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> By October 2017, a 2,000-km fiber line was operational between [[Beijing]], [[Jinan]], [[Hefei]] and [[Shanghai]].<ref name="insidescience">{{cite web |url = https://www.insidescience.org/news/china-leader-quantum-communications |title = Is China the Leader in Quantum Communications? | author = Yuen Yiu | date=19 January 2018 |access-date=19 March 2018 |website=[[Institute of Electrical and Electronics Engineers|IEEE]]}}</ref> Together they constitute the world's first space-ground quantum network.<ref name="ieee">{{cite web |url = https://spectrum.ieee.org/china-successfully-demonstrates-quantum-encryption-by-hosting-a-video-call |title = China Demonstrates Quantum Encryption By Hosting a Video Call | author = Amy Nordrum |date=3 October 2017 |access-date=17 March 2018 |website=[[Institute of Electrical and Electronics Engineers|IEEE]]}}</ref> Up to 10 Micius/QUESS satellites are expected,<ref name="sciencenews">{{cite web |url = https://www.sciencenews.org/article/global-quantum-communication-top-science-stories-2017-yir |title = A quantum communications satellite proved its potential in 2017 | author = Jian-Wei Pan |date=3 October 2017 |access-date=19 March 2018 |website=[[Science News]]}}</ref> allowing a European–Asian [[Quantum network|quantum-encrypted network]] by 2020, and a global network by 2030.<ref name="Xinhua">{{cite news|url=http://news.xinhuanet.com/english/2016-08/16/c_135604287.htm |archive-url=https://web.archive.org/web/20160817155904/http://news.xinhuanet.com/english/2016-08/16/c_135604287.htm |url-status=dead |archive-date=17 August 2016 |title=China Focus: China's space satellites make quantum leap |author=huaxia|date=16 August 2016|access-date=17 August 2016|publisher=Xinhua}}</ref><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>

==== Tokyo QKD Network ====
The Tokyo QKD Network<ref>{{Cite web|url=http://www.uqcc2010.org/highlights/index.html|title=UQCC2010 - Updating Quantum Cryptography and Communications 2010 &#124; Tokyo QKD Network|website=www.uqcc2010.org}}</ref> was inaugurated on the first day of the UQCC2010 conference. The network involves an international collaboration between 7 partners; [[NEC]], [[Mitsubishi Electric]], [[Nippon Telegraph and Telephone|NTT]] and [[National Institute of Information and Communications Technology|NICT]] from Japan, and participation from Europe by Toshiba Research Europe Ltd. (UK), Id Quantique (Switzerland) and All Vienna (Austria). "All Vienna" is represented by researchers from the [[Austrian Institute of Technology]] (AIT), the [[Institute for Quantum Optics and Quantum Information]] (IQOQI) and the [[University of Vienna]].

==== Los Alamos National Laboratory ====
A hub-and-spoke network has been operated by Los Alamos National Laboratory since 2011. All messages are routed via the hub. The system equips each node in the network with quantum transmitters—i.e., lasers—but not with expensive and bulky photon detectors. Only the hub receives quantum messages. To communicate, each node sends a one-time pad to the hub, which it then uses to communicate securely over a classical link. The hub can route this message to another node using another one time pad from the second node. The entire network is secure only if the central hub is secure. Individual nodes require little more than a laser: Prototype nodes are around the size of a box of matches.<ref>{{cite arXiv|eprint=1305.0305|last1=Hughes|first1=Richard J.|last2=Nordholt|first2=Jane E.|author2-link=Beth Nordholt|last3=McCabe|first3=Kevin P.|last4=Newell|first4=Raymond T.|last5=Peterson|first5=Charles G.|last6=Somma|first6=Rolando D.|title=Network-Centric Quantum Communications with Application to Critical Infrastructure Protection|class=quant-ph|year=2013}}</ref>

==== Singapore's National Quantum-Safe Network Plus (NQSN+) ====
Following the successful [http://www.nqsn.sg National Quantum-Safe Network] Testbed trials, National Quantum-Safe Network Plus (NQSN+) was launched by IMDA in 2023 and is part of Singapore's Digital Connectivity Blueprint, which outlines the next bound of Singapore's digital connectivity to 2030. NQSN+ will support network operators to deploy quantum-safe networks nationwide, granting businesses easy access to quantum-safe solutions that safeguard their critical data. The NQSN+ will start with two network operators, Singtel and SPTel, together with SpeQtral. Each will build a nationwide, interoperable quantum-safe network that can serve all businesses. Businesses can work with NQSN+ operators to integrate quantum-safe solutions such as Quantum Key Distribution (QKD) and Post-Quantum Cryptography (PQC) and be secure in the quantum age.<ref>{{cite web | url = https://www.imda.gov.sg/about-imda/emerging-technologies-and-research/national-quantum-safe-network-plus | website = imda.gov.sg | title =  Singapore's National Quantum-Safe Network Plus (NQSN+) | first = IMDA | last = Singapore | date = 21 August 2024}}</ref>

==== Eagle-1 ====

In late 2025 or 2026, the [[European Space Agency|ESA]] plans to launch the satellite Eagle-1, an experimental space-based quantum key distribution system.<ref>{{cite web | url = https://www.esa.int/Applications/Connectivity_and_Secure_Communications/Eagle-1 | website = esa.int | title = Eagle-1 |access-date = 4 March 2025}}</ref>