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In physics, Bose–Einstein correlations〔Richard M. Weiner, Introduction to Bose–Einstein Correlations and Subatomic Interferometry, John Wiley, 2000.〕〔Richard M. Weiner, Bose–Einstein Correlations in Particle and Nuclear Physics, A Collection of Reprints, John Wiley, 1997, ISBN 0-471-96979-6.〕 are correlations between identical bosons. They have important applications in astronomy, optics, particle and nuclear physics. == From intensity interferometry to Bose–Einstein correlations == The interference between two (or more) waves establishes a correlation between these waves. In particle physics, in particular, where to each particle there is associated a wave, we encounter thus interference and correlations between two (or more) particles, described mathematically by second or higher order correlation functions.〔The correlation function of order n defines the transition amplitudes between states containing n particles.〕 These correlations have quite specific properties for identical particles. We then distinguish Bose–Einstein correlations for bosons and Fermi–Dirac correlations for fermions. While in Fermi–Dirac second order correlations the particles are antibunched, in Bose–Einstein correlations (BEC)〔In this article the abbreviation BEC is reserved exclusively for Bose–Einstein correlations, not to be confused with that sometimes used in the literature for Bose–Einstein condensates.〕 they are bunched. Another distinction between Bose–Einstein and Fermi–Dirac correlation is that only BEC can present quantum coherence (cf. below). In optics two beams of light are said to interfere coherently, when the phase difference between their waves is constant; if this phase difference is random or changing the beams are incoherent. The coherent superposition of wave amplitudes is called first order interference. In analogy to that we have intensity or second order Hanbury Brown and Twiss (HBT) interference, which generalizes the interference between amplitudes to that between squares of amplitudes, i.e. between intensities. In optics amplitude interferometry is used for the determination of lengths, surface irregularities and indexes of refraction; intensity interferometry, besides presenting in certain cases technical advantages (like stability) as compared with amplitude interferometry, allows also the determination of quantum coherence of sources. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bose–Einstein correlations」の詳細全文を読む スポンサード リンク
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