Khác biệt giữa bản sửa đổi của “Ngưng tụ Bose-Einstein”
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[[Tập tin:Bose Einstein condensate.png|nhỏ|350px|Trạng thái đông đặc Bose-Einstein của các boson, trong trường hợp này là các [[nguyên tử]] [[rubiđi|rubidi]]. Hình vẽ là phân bố [[tốc độ]] của chuyển động của các nguyên tử, theo vị trí. Màu đỏ chỉ nguyên tử di chuyển nhanh, màu xanh và trắng chỉ nguyên tử di chuyển chậm. Trái: trước khi có động đặc Bose-Einstein. Giữa: ngay sau khi đông đặc. Phải: trạng thái đông đặc mạnh hơn. Ở trạng thái đông đặc, rất nhiều nguyên tử có cùng vận tốc và vị trí (cùng [[trạng thái lượng tử]]) nằm ở đỉnh màu trắng.]]
A '''Bose–Einstein condensate (BEC)''' is a [[state of matter]] of a dilute gas of [[boson]]s cooled to [[temperature]]s very close to [[absolute zero]] (that is, very near {{val|0|u=K}} or {{val|-273.15|u=°C}}<ref>{{cite book | title=Thermodynamics | first1=C. P. | last1=Arora | publisher=Tata McGraw-Hill | year=2001 | isbn=0-07-462014-2 |page=43 | url=http://books.google.com/books?id=w8GhW3J8RHIC}}, [http://books.google.com/books?id=w8GhW3J8RHIC&pg=PA43 Table 2.4 page 43]</ref>). Under such conditions, a large fraction of the bosons occupy the lowest [[quantum state]], at which point [[quantum]] effects become apparent on a [[macroscopic scale]]. These effects are called [[macroscopic quantum phenomena]].
Although later experiments have revealed complex interactions, this state of matter was first predicted, generally, in papers by [[Satyendra Nath Bose]] and [[Albert Einstein]] in 1924–25. Bose first sent a paper to Einstein on the [[quantum statistics]] of light quanta (now called [[photon]]s). Einstein was impressed, translated the paper himself from English to German and submitted it for Bose to the ''[[Zeitschrift für Physik]]'', which published it. (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 |accessdate=23 March 2011}}</ref>). Einstein then extended Bose's ideas to material particles (or matter) in two other papers.<ref>{{cite book |first=Ronald W. |last=Clark |title=Einstein: The Life and Times |publisher=Avon Books |year=1971 |pages=408–409 |isbn=0-380-01159-X }}</ref> The result of the efforts of Bose and Einstein 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 known as [[bosons]]. Bosonic particles, which include the photon as well as atoms such as [[helium-4]] (<sup>4</sup>He), are allowed to share quantum states with each other. Einstein demonstrated 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.
In 1938 [[Fritz London]] proposed BEC as a mechanism for [[superfluidity]] in <sup>4</sup>He and [[superconductivity]].<ref>{{cite journal |first=F. |last=London |title=The λ-Phenomenon of Liquid Helium and the Bose–Einstein Degeneracy |journal=[[Nature (journal)|Nature]] |volume=141 |issue=3571 |pages=643–644 |year=1938 |doi=10.1038/141643a0 |bibcode = 1938Natur.141..643L }}</ref><ref>London, F. ''Superfluids'' Vol.I and II, (reprinted New York: Dover 1964)</ref>
In 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, using a gas of [[rubidium]] atoms cooled to 170 [[kelvin|nanokelvin]] (nK) <ref>{{cite web|title = New State of Matter Seen Near Absolute Zero|url=http://physics.nist.gov/News/Update/950724.html|publisher=NIST}}</ref> ({{val|1.7|e=-7|u=K}}). For their achievements Cornell, Wieman, and [[Wolfgang Ketterle]] at [[MIT]] received the 2001 [[Nobel Prize in Physics]].<ref>{{cite web | last = Levi | first = Barbara Goss | 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 | accessdate = 26 January 2008 |archiveurl =http://web.archive.org/web/20071024134547/http://www.physicstoday.org/pt/vol-54/iss-12/p14.html |archivedate = 24 October 2007}}</ref> In November 2010 the first photon BEC was observed.<ref>{{cite journal|doi=10.1038/nature09567|title=Bose–Einstein condensation of photons in an optical microcavity|year=2010|last1=Klaers|first1=Jan|last2=Schmitt|first2=Julian|last3=Vewinger|first3=Frank|last4=Weitz|first4=Martin|journal=Nature|volume=468|issue=7323|pages=545–548|pmid=21107426|bibcode = 2010Natur.468..545K |arxiv = 1007.4088 }}</ref> In 2012, the theory of the photon BEC was developed.<ref>{{cite journal |last=Sob'yanin |first=D. N. |year=2013 |title=Theory of Bose-Einstein condensation of light in a microcavity |journal=[[Bulletin of the Lebedev Physics Institute|Bull. Lebedev Phys. Inst.]] |volume=40 |issue=4 |pages=91–96 |arxiv=1308.4089 |bibcode=2013BLPI...40...91S |doi=10.3103/S1068335613040039}}</ref><ref>{{cite journal |last=Sob'yanin |first=Denis Nikolaevich |year=2013 |title=Bose-Einstein condensation of light: General theory |journal=[[Physical Review E|Phys. Rev. E]] |volume=88 |issue=2 |pages=022132 |arxiv=1308.4090 |pmid=24032800 |bibcode=2013PhRvE..88b2132S |doi=10.1103/PhysRevE.88.022132}}</ref>
This transition to BEC occurs below a critical temperature, which for a uniform [[Three-dimensional space|three-dimensional]] gas consisting of non-interacting particles with no apparent internal degrees of freedom is given by:
:<math>T_c=\left(\frac{n}{\zeta(3/2)}\right)^{2/3}\frac{2\pi \hbar^2}{ m k_B} \approx 3.3125 \ \frac{\hbar^2 n^{2/3}}{m k_B} </math>
where:
<dl><dd>
{|cellspacing="0" cellpadding="0"
|-
| <math>\,T_c</math>
| is
| the critical temperature,
|-
| <math>\,n</math>
| is
| the [[Number density|particle density]],
|-
| <math>\,m</math>
| is
| the mass per boson,
|-
| <math>\hbar</math>
| is
| the reduced [[Planck constant]],
|-
| <math>\,k_B</math>
| is
| the [[Boltzmann constant]], and
|-
| <math>\,\zeta</math>
| is
| the [[Riemann zeta function]]; <math>\,\zeta(3/2)\approx 2.6124.</math> <ref>{{OEIS|id=A078434}}</ref>
|}
</dd></dl>
== Giới thiệu ==
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