Editing Bose–Einstein condensate (section)

=== Isotopes ===
Bose-Einstein condensation has mainly been observed on alkaline atoms, some of which have collisional properties particularly suitable for evaporative cooling in traps, and which were the first to be laser-cooled. As of 2021, using ultra-low temperatures of {{val|e=-7|u=K}} or below, Bose–Einstein condensates had been obtained for a multitude of isotopes with more or less ease, mainly of [[alkali metal]], [[alkaline earth metal]], and [[lanthanide]] atoms ({{SimpleNuclide|lithium|7|link=yes}}, {{SimpleNuclide|sodium|23|link=yes}}, {{SimpleNuclide|potassium|39|link=yes}}, {{SimpleNuclide|potassium|41|link=yes}}, {{SimpleNuclide|rubidium|85|link=yes}}, {{SimpleNuclide|Rubidium|87|link=yes}}, {{SimpleNuclide|caesium|133|link=yes}}, {{SimpleNuclide|chromium|52|link=yes}}, {{SimpleNuclide|calcium|40|link=yes}}, {{SimpleNuclide|strontium|84|link=yes}}, {{SimpleNuclide|strontium|86|link=yes}}, {{SimpleNuclide|strontium|88|link=yes}}, {{SimpleNuclide|ytterbium|170|link=yes}}, {{SimpleNuclide|ytterbium|174|link=yes}}, {{SimpleNuclide|ytterbium|176|link=yes}}, {{SimpleNuclide|dysprosium|164|link=yes}}, {{SimpleNuclide|erbium|168|link=yes}}, {{SimpleNuclide|thulium|169|link=yes}}, and metastable {{SimpleNuclide|helium|4|link=yes}} (orthohelium)).<ref>{{cite journal | last1=Schreck | first1=Florian | last2=Druten | first2=Klaasjan van | title=Laser cooling for quantum gases | journal=Nature Physics | volume=17 | issue=12 | date=2021 | issn=1745-2473 | doi=10.1038/s41567-021-01379-w | pages=1296–1304| arxiv=2209.01026 }}</ref><ref>{{cite thesis |last=Stellmer |first=Simon |date=2013 |title=Degenerate quantum gases of strontium |degree=PhD |publisher=University of Innsbruck|url=http://www.ultracold.at/theses/2013-stellmer.pdf}}</ref> Research was finally successful in atomic hydrogen with the aid of the newly developed method of 'evaporative cooling'.<ref>
{{cite journal
 |author1=Dale G. Fried
 |author2=Thomas C. Killian
 |author3=Lorenz Willmann
 |author4=David Landhuis
 |author5=Stephen C. Moss
 |author6=Daniel Kleppner
 |author7=Thomas J. Greytak |name-list-style=amp
 |year=1998
 |title=Bose–Einstein Condensation of Atomic Hydrogen
 |journal=Phys. Rev. Lett.
 |volume=81 |issue=18 |pages=3811
 |doi=10.1103/PhysRevLett.81.3811 |bibcode=1998PhRvL..81.3811F|arxiv = physics/9809017 |s2cid=3174641
 }}
</ref>

In contrast, the superfluid state of {{SimpleNuclide|Helium|4|link=yes}} below {{val|2.17|u=K}} is differs significantly from dilute degenerate atomic gases because the interaction between the atoms is strong. Only 8% of atoms are in the condensed fraction near absolute zero, rather than near 100% of a weakly interacting BEC.<ref>{{cite web | url=https://www.nobelprize.org/nobel_prizes/physics/laureates/2001/advanced-physicsprize2001.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.nobelprize.org/nobel_prizes/physics/laureates/2001/advanced-physicsprize2001.pdf |archive-date=2022-10-09 |url-status=live| title=Bose–Einstein Condensation in Alkali Gases | publisher=The Royal Swedish Academy of Sciences | date=2001 | access-date = 17 April 2017 }}</ref>

The [[boson]]ic behavior of some of these alkaline gases appears odd at first sight, because their nuclei have half-integer total spin. It arises from the interplay of electronic and nuclear spins: at ultra-low temperatures and corresponding excitation energies, the half-integer total spin of the electronic shell (one outer electron) and half-integer total spin of the nucleus are coupled by a very weak [[hyperfine structure|hyperfine interaction]].<ref name="f953">{{cite book | last=Dunlap | first=Richard A. | title=Lasers and Their Application to the Observation of Bose-Einstein Condensates | publisher=Iop Concise Physics | date=2019-09-04 | isbn=978-1-64327-693-9 | page=}}</ref> The total spin of the atom, arising from this coupling, is an integer value.<ref>The chemistry of systems at room temperature is determined by the electronic properties, which is essentially fermionic, since room temperature thermal excitations have typical energies much higher than the hyperfine values.</ref> Conversely, alkali isotopes which have an integer nuclear spin (such as {{SimpleNuclide|lithium|6|link=yes}} and {{SimpleNuclide|potassium|40|link=yes}}) are fermions and can form degenerate [[Fermi gas]]es, also called "Fermi condensates".<ref>{{cite conference | last=Greiner | first=Markus | title=AIP Conference Proceedings | chapter=Fermionic Condensates | publisher=AIP | volume=770 | date=2005 | doi=10.1063/1.1928855 | pages=209–217| arxiv=cond-mat/0502539 }}</ref>

Cooling [[fermion]]s to extremely low temperatures has created [[degenerate matter|degenerate]] gases, subject to the [[Pauli exclusion principle]]. To exhibit Bose–Einstein condensation, the fermions must "pair up" to form bosonic compound particles (e.g. [[molecule]]s or [[BCS theory|Cooper pairs]]). The first [[molecule|molecular]] condensates were created in November 2003 by the groups of [[Rudolf Grimm]] at the [[University of Innsbruck]], [[Deborah S. Jin]] at the [[University of Colorado at Boulder]] and [[Wolfgang Ketterle]] at [[Massachusetts Institute of Technology|MIT]]. Jin quickly went on to create the first [[fermionic condensate]], working with the same system but outside the molecular regime.<ref>{{cite web | url=http://physicsworld.com/cws/article/news/2004/jan/28/fermionic-condensate-makes-its-debut|title=Fermionic condensate makes its debut| publisher=Physicsweb.org | date=28 January 2004 }}</ref>