Editing Bose–Einstein condensate (section)

== History ==
[[File:Bose Einstein condensate.png|right|thumb|238px|Velocity-distribution data (3 views) for gas of [[rubidium]] atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate. {{nowrap|Left: just}} before the appearance of a Bose–Einstein condensate. {{nowrap|Center: just}} after the appearance of the condensate. {{nowrap|Right: after}} further evaporation, leaving a sample of nearly pure condensate.]]

Bose first sent a paper to Einstein on the [[quantum statistics]] of light quanta (now called [[photon]]s), in which he derived [[Planck's law|Planck's quantum radiation law]] without any reference to classical physics. Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the ''[[Zeitschrift für Physik]]'', which published it in 1924.<ref>{{cite journal |author=S. N. Bose |year=1924 |title=Plancks Gesetz und Lichtquantenhypothese |language=de |journal=Zeitschrift für Physik |volume=26 |issue=1 |pages=178–181 |bibcode=1924ZPhy...26..178B |doi=10.1007/BF01327326 |s2cid=186235974 }}</ref> (The Einstein manuscript, once believed to be lost, was found in a library at [[Leiden University]] in 2005.<ref>{{cite web |url=http://www.lorentz.leidenuniv.nl/history/Einstein_archive/ |title=Leiden University Einstein archive |publisher=Lorentz.leidenuniv.nl |date=27 October 1920 |access-date=23 March 2011}}</ref>) Einstein then extended Bose's ideas to matter in two other papers.<ref>{{cite journal |author=A. Einstein |year=1925 |title=Quantentheorie des einatomigen idealen Gases |language=de |journal=Sitzungsberichte der Preussischen Akademie der Wissenschaften |volume=1 |page=3}}</ref><ref>{{cite book |first=Ronald W. |last=Clark |title=Einstein: The Life and Times |publisher=Avon Books |year=1971 |pages=[https://archive.org/details/einstein00rona/page/408 408–409] |isbn=978-0-380-01159-9 |url-access=registration |url=https://archive.org/details/einstein00rona/page/408 }}</ref> The result of their efforts is the concept of a [[Bose gas]], governed by [[Bose–Einstein statistics]], which describes the statistical distribution of [[identical particles]] with [[integer]] [[Spin (physics)|spin]], now called [[boson]]s. Bosons are allowed to share a quantum state. Einstein proposed that cooling bosonic atoms to a very low temperature would cause them to fall (or "condense") into the lowest accessible [[quantum state]], resulting in a new form of matter. Bosons include the [[photon]], [[polariton]]s, [[magnon]]s, some [[atom]]s and [[molecule]]s (depending on the number of [[nucleon]]s, see [[#Isotopes]]) such as atomic hydrogen, [[helium-4]], lithium-7, rubidium-87 or strontium-84.

In 1938, [[Fritz London]] proposed the BEC as a mechanism for [[superfluidity]] in {{SimpleNuclide|Helium|4}} and [[superconductivity]].<ref name=London:1938/><ref>London, F. ''Superfluids'', Vol. I and II, (reprinted New York: Dover 1964).</ref>

The quest to produce a Bose–Einstein condensate in the laboratory was stimulated by a paper published in 1976 by two program directors at the [[National Science Foundation]] (William Stwalley and Lewis Nosanow), proposing to use spin-polarized atomic [[hydrogen]] to produce a gaseous BEC.<ref>{{cite journal |last1=Stwalley |first1=W. |date=12 April 1976 |title=Possible "New" Quantum Systems |journal=Physical Review Letters |volume=36 |issue=15 |pages=910–913 |bibcode=1976PhRvL..36..910S |doi=10.1103/PhysRevLett.36.910}}</ref> This led to the immediate pursuit of the idea by four independent research groups; these were led by Isaac Silvera ([[University of Amsterdam]]), Walter Hardy ([[University of British Columbia]]), Thomas Greytak ([[Massachusetts Institute of Technology]]) and David Lee ([[Cornell University]]).<ref>{{cite arXiv |last1=Cornell |first1=E. |title=Experiments in Dilute Atomic Bose–Einstein Condensation |date=1999 |eprint=cond-mat/9903109}}</ref> However, cooling atomic hydrogen turned out to be technically difficult, and Bose-Einstein condensation of atomic hydrogen was only realized in 1998.<ref name="v594">{{cite journal | last1=Fried | first1=Dale G. | last2=Killian | first2=Thomas C. | last3=Willmann | first3=Lorenz | last4=Landhuis | first4=David | last5=Moss | first5=Stephen C. | last6=Kleppner | first6=Daniel | last7=Greytak | first7=Thomas J. | title=Bose-Einstein Condensation of Atomic Hydrogen | journal=Physical Review Letters | volume=81 | issue=18 | date=1998-11-02 | issn=0031-9007 | doi=10.1103/PhysRevLett.81.3811 | pages=3811–3814| arxiv=physics/9908044 }}</ref><ref name="m380">{{cite journal | last1=Greytak | first1=T.J | last2=Kleppner | first2=D | last3=Fried | first3=D.G | last4=Killian | first4=T.C | last5=Willmann | first5=L | last6=Landhuis | first6=D | last7=Moss | first7=S.C | title=Bose–Einstein condensation in atomic hydrogen | journal=Physica B: Condensed Matter | volume=280 | issue=1–4 | date=2000 | doi=10.1016/S0921-4526(99)01415-5 | pages=20–26 | url=http://web.mit.edu/physics/greytak-kleppner/publications/LT22_Talk.pdf}}</ref>

On 5 June 1995, the first gaseous condensate was produced by [[Eric Allin Cornell|Eric Cornell]] and [[Carl Wieman]] at the [[University of Colorado at Boulder]] [[National Institute of Standards and Technology|NIST]]–[[JILA]] lab, in a gas of [[rubidium]] atoms cooled to 170&nbsp;[[kelvin|nanokelvins]] (nK).<ref name=":0">{{Cite journal |last1=Anderson |first1=M. H. |last2=Ensher |first2=J. R. |last3=Matthews |first3=M. R. |last4=Wieman |first4=C. E. |last5=Cornell |first5=E. A. |date=1995-07-14 |title=Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor |journal=Science |language=en |volume=269 |issue=5221 |pages=198–201 |doi=10.1126/science.269.5221.198 |issn=0036-8075 |pmid=17789847 |bibcode=1995Sci...269..198A |doi-access=free}}</ref> Shortly thereafter, [[Wolfgang Ketterle]] at MIT produced a Bose–Einstein Condensate in a gas of [[sodium]] atoms. For their achievements Cornell, Wieman, and Ketterle received the 2001 [[Nobel Prize in Physics]].<ref>{{cite web |last = Levi |first = Barbara Goss |author-link=Barbara Goss Levi |title = Cornell, Ketterle, and Wieman Share Nobel Prize for Bose–Einstein Condensates |work = Search & Discovery |publisher = Physics Today online |year = 2001 |url = http://www.physicstoday.org/pt/vol-54/iss-12/p14.html |access-date = 26 January 2008 |archive-url = https://archive.today/20071024134547/http://www.physicstoday.org/pt/vol-54/iss-12/p14.html |archive-date = 24 October 2007}}</ref> Bose-Einstein condensation of alkali gases is easier because they can be pre-cooled with [[laser cooling]] techniques, unlike atomic hydrogen at the time, which give a significant head start when performing the final forced evaporative cooling to cross the condensation threshold.<ref name="m380" /> These early studies founded the field of [[ultracold atom]]s, and hundreds of research groups around the world now routinely produce BECs of dilute atomic vapors in their labs.

Since 1995, many other atomic species have been condensed (see [[#Isotopes]]), and BECs have also been realized using molecules, [[polariton]]s, and other quasi-particles. BECs of photons can be made, for example, in dye microcavites with wavelength-scale mirror separation, forming a two-dimensional harmonically confined photon gas with tunable chemical potential.<ref name=Klaers:2010/> BEC of plasmonic quasiparticles (plasmon-exciton polaritons) has been realized in periodic arrays of metal nanoparticles overlaid with dye molecules,<ref name=Hakala:2018/> exhibiting ultrafast sub-picosecond dynamics<ref name=Väkeväinen:2020/> and long-range correlations.<ref name=Moilanen:2021/>