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The '''''[[Hanbury Brown]]―Twiss effect''''' is one of the most beautiful results of [[modern Physics]]: the 20th century [[Eratosthenes]] experiment (the one with the shadow). | The '''''[[Hanbury Brown]]―Twiss effect''''' is one of the most beautiful results of [[modern Physics]]: the 20th century [[Eratosthenes]] experiment (the one with the shadow). | ||
| − | It | + | It arises from the fact that when waves interfere—a well-known and understood process—they develop correlations. This surprisingly escaped notice until a young engineer working for British intelligence ([[Hanbury Brown]]) got a grip on the effect to create a new type of stellar interferometer out of it. |
| − | It is a subtle effect of | + | As a result, in a modern (quantum-mechanical) picture, bosons have a tendency to be detected together ("bunching"). This occurs on scales that span from stars ($10^{12}$cm, for which the first underlying technique was initially developed) to nuclear matter ($10^{-12}$cm).{{cite|baym98a}} |
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| + | In [[Optics]], this relates to photons from thermal sources (so, natural ones: lightbulbs, stars, etc.) arriving together on the photodetector. This is surprising because you would expect them to be uncorrelated. | ||
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| + | It is a subtle and counter-intuitive effect of interferences, which needed all the insights, wit and persistence of a young engineer to be discovered in the form of an intensity interference, centuries after wave (or field) interferences (by [[Huygens]], [[Fresnel]] and others). This was quickly understood (by [[Purcell]]) to be a particular case of quanta correlations{{cite|purcell56a}} and became the seed for the field of [[quantum optics]]. | ||
It is also a capital story in the [[History of Science]], with drama, coup de théâtres, and a beautiful moral. | It is also a capital story in the [[History of Science]], with drama, coup de théâtres, and a beautiful moral. | ||
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== References == | == References == | ||
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<references /> | <references /> | ||
Contents |
The Hanbury Brown―Twiss effect is one of the most beautiful results of modern Physics: the 20th century Eratosthenes experiment (the one with the shadow).
It arises from the fact that when waves interfere—a well-known and understood process—they develop correlations. This surprisingly escaped notice until a young engineer working for British intelligence (Hanbury Brown) got a grip on the effect to create a new type of stellar interferometer out of it.
As a result, in a modern (quantum-mechanical) picture, bosons have a tendency to be detected together ("bunching"). This occurs on scales that span from stars ($10^{12}$cm, for which the first underlying technique was initially developed) to nuclear matter ($10^{-12}$cm).[1]
In Optics, this relates to photons from thermal sources (so, natural ones: lightbulbs, stars, etc.) arriving together on the photodetector. This is surprising because you would expect them to be uncorrelated.
It is a subtle and counter-intuitive effect of interferences, which needed all the insights, wit and persistence of a young engineer to be discovered in the form of an intensity interference, centuries after wave (or field) interferences (by Huygens, Fresnel and others). This was quickly understood (by Purcell) to be a particular case of quanta correlations[2] and became the seed for the field of quantum optics.
It is also a capital story in the History of Science, with drama, coup de théâtres, and a beautiful moral.
Hanbury Brown was an engineer working for British intelligence when he got the idea of intensity correlations by noticing similarities of the wiggles made by the radar signal on oscilloscopes. After the war, he got to bring this idea to build a radio-wave interferometer and indeed could implement the technique[3] at Jodrell bank. He sought assistance from a pure Mathematician, Richard Quintin Twiss, of whom very little is known in comparison. Together they developed the theory,[4] interestingly, despite initial negative results from Twiss who calculated this would not work out (Hanbury convinced him otherwise!)
They then turned to the optical field, which was quite a natural continuation, but this exerted very much opposition from physicists (remember, Hanbury was an engineer and Twiss a mathematician), even though they managed to demonstrate the effect experimentally,[5] with five-foot diameter searchlights left over from the Second World War.
The controversy was put to rest by Purcell[2] who argued that the effect ought to be expected from the symmetry of the wavefunction, and also predicted that the opposite anticorrelations would thus result for fermionic (anti-symmetrized) wavefunctions.
The technique was subsequently applied to astronomy in the visible spectrum, with the measurement of the angular size of Sirius (α Canus Majoris A).[6]
Hanbury Brown's main papers on this topic with Twiss are (note that the opening one is not with Twiss):
He also has a four-part series with Twiss, which I have not studied yet: