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Thomas Klimpel
Thomas Klimpel
12:11 AM
Hanbury Brown and Twiss effect
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 wave–particle duality 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...
 
 
3 hours later…
vzn
vzn
3:35 AM
@ThomasKlimpel have looked at HBT quite a bit over the years. HBT is a strong hint that QM is "not all what it seems"... it doesnt seem to be expressed fundamentally in QM formalism... yet it seems to be a fundamental aspect of measurement. oh, and it reminds me of a key thought experiment of Einstein that doesnt get a lot of attn... did see a new paper on that but itd take awhile to find/ dig up... it seems to directly relate to it yet havent seen others point out this connection...
 
 
5 hours later…
Thomas Klimpel
Thomas Klimpel
8:09 AM
A simple argument suggested by Ugo Fano [Fano, 1961] captures the essence of the quantum explanation. Consider two points a and b in a source that emit photons detected by two detectors A and B as in the diagram. A joint detection takes place when the photon emitted by a is detected by A and the photon emitted by b is detected by B (red arrows) or when a's photon is detected by B and b's by A (green arrows).
The quantum mechanical probability amplitudes for these two possibilities are denoted by ⟨ A | a ⟩ ⟨ B | b ⟩ and ⟨ B | a ⟩ ⟨ A | b ⟩ respectively. If the photons are indistinguishable, the two amplitudes interfere constructively to give a joint detection probability greater than that for two independent events. The sum over all possible pairs a, b in the source washes out the interference unless the distance AB is sufficiently small.
Two source points a and b emit photons detected by detectors A and B. The two colors represent two different ways to detect two photons.

Fano's explanation nicely illustrates the necessity of considering two-particle amplitudes, which are not as intuitive as the more familiar single-particle amplitudes used to interpret most interference effects. This may help to explain why some physicists in the 1950s had difficulty accepting the Hanbury Brown and Twiss result.
 
 
1 hour later…
Thomas Klimpel
Thomas Klimpel
9:22 AM
@vzn In a certain sense, you are much deeper into QM than me, and for a much longer time. I came across HBT in Feynman's QED book, and I had to google it because I simply had trouble believing what Feynman said. Yesterday I talked with a colleague about interpretation of mathematics and physics, and I claimed that mathematics must secretly always be interpreted instrumentalistically. He said that this would be the same for physics, so I tried to remember...
... the name of that effect (HBT) which shows that my preferred instrumentalistic interpretation of QM is insufficient, and that there is some reality of the wavefunction with observable effects (a systematic pattern instead of mere noise) deep below the predictions of my instrumentalistic interpretation.
The critical point is that for my instrumentalistic interpretation a and b are simply independent (and therefore incoherent), but the deeper wavefunction picture requires taking products of the individual ("independent") wavefunctions, i.e. ⟨ A | a ⟩ ⟨ B | b ⟩ and ⟨ B | a ⟩ ⟨ A | b ⟩, and computing an interference pattern of those products.
 
 
5 hours later…
vzn
vzn
2:36 PM
@ThomasKlimpel believe there is a classical system with "nearly" the same math. the essence is counterintuitive emergent properties. have some key refs that tend to agree. have outlined it over the years, nobody has grasped it so far. still looking for a dedicated cohort to follow through. it would seem that sometimes human nature is more to wonder about curiosities than solve them. btw that said am sure you know more about some aspects of QM than me :)
 
 
2 hours later…
vzn
vzn
4:24 PM
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