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In physics, the Hanbury Brown and Twiss (HBT) effect is any of a variety of correlation and anti-correlation effects in the intensities received by two detectors from a beam of particles. HBT effects can generally be attributed to the dual wave-particle nature of the beam, and the results of a given experiment depend on whether the beam is composed of fermions or bosons. Devices which use the effect are commonly called intensity interferometers and were originally used in astronomy, although they are also heavily used in the field of quantum optics. == History == In 1956, Robert Hanbury Brown and Richard Q. Twiss published ''A test of a new type of stellar interferometer on Sirius'', in which two photomultiplier tubes (PMTs), separated by about 6 meters, were aimed at the star Sirius. Light was collected into the PMTs using mirrors from searchlights. An interference effect was observed between the two intensities, revealing a positive correlation between the two signals, despite the fact that no phase information was collected. Hanbury Brown and Twiss used the interference signal to determine the apparent angular size of Sirius, claiming excellent resolution. Also, in the field of particle physics, Goldhaber et al. performed an experiment in 1959 in Berkeley and found an unexpected angular correlation among identical pions, discovering the ρ0 resonance, by means of decay.〔''Phys.Rev.Lett''.3,p181(1959)〕 From then on, the HBT technique started to be used by the heavy-ion community to determine the space-time dimensions of the particle emission source for heavy ion collisions. For recent developments in this field, cf. for example the review article by Lisa.〔M.Lisa,et al., ''Ann.Rev.Nucl.Part.Sci'' 55, p357(2005), (ArXiv 0505014 )〕 The original HBT result met with much skepticism in the physics community. Although intensity interferometry had been widely used in radio astronomy where Maxwell's equations are valid, at optical wavelengths the light would be quantised into a relatively small number of photons. Many physicists worried that the correlation was inconsistent with the laws of thermodynamics. Some even claimed that the effect violated the uncertainty principle. Hanbury Brown and Twiss resolved the dispute in a neat series of papers (see References below) which demonstrated, first, that wave transmission in quantum optics had exactly the same mathematical form as Maxwell's equations albeit with an additional noise term due to quantisation at the detector, and secondly, that according to Maxwell's equations, intensity interferometry should work. Others, such as Edward Mills Purcell immediately supported the technique, pointing out that the clumping of bosons was simply a manifestation of an effect already known in statistical mechanics. After a number of experiments, the whole physics community agreed that the observed effect was real. The original experiment used the fact that two bosons tend to arrive at two separate detectors at the same time. Morgan and Mandel used a thermal photon source to create a dim beam of photons and observed the tendency of the photons to arrive at the same time on a single detector. Both of these effects used the wave nature of light to create a correlation in arrival time - if a single photon beam is split into two beams, then the particle nature of light requires that each photon is only observed at a single detector, and so an anti-correlation was observed in 1986. Finally, bosons have a tendency to clump together, giving rise to Bose–Einstein correlations, while fermions due to the Pauli exclusion principle, tend to spread apart leading to Fermi–Dirac (anti)correlations. Bose–Einstein correlations have been observed between pions, kaons and photons, and Fermi–Dirac (anti)correlations between protons, neutrons and electrons. For a general introduction in this field cf. the textbook on Bose–Einstein correlations by Richard M. Weiner 〔Richard M. Weiner, Introduction to Bose–Einstein Correlations and Subatomic Interferometry, John Wiley, 2000〕 A difference in repulsion of BECs in the "trap-and-free fall" analogy of the HBT effect〔Comparison of the Hanbury Brown-Twiss effect for bosons and fermions - http://arxiv.org/abs/cond-mat/0612278〕 affects comparison. 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「Hanbury Brown and Twiss effect」の詳細全文を読む スポンサード リンク
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