The Hanbury Brown and Twiss (HB&T) experiment was done properly with photons. The team of Aspect performed with fermions experiments that have some analogy with the HB&T experiment in the sense that they reveal the anti-bunching property of identical fermions. However, as far as I know, an HB&T-type experiment, in the original form - see attached picture, was never done with fermions.
For experimenting with fermions, intense and monochromatic sources of slow fermions are needed. Does somebody know such sources?
Unfortunately, clean results can be obtained if the detectors are very far from the two sources, s.t. neutrons are not useful because they are unstable.
Hint: because of the need of big distance from sources to detectors, I thought that one can eventually produce in some way strong beams of fermions, and then pass them between two mirrors and let them be reflected repeatedly before getting out from there. However, for a clear HB&T effect, the beams have also to be of low energy of sharp distribution. So, since I am no experimenter, I don't know how the beams can be filtered for obtaining the desired distribution. (Remi Cornwall has kindly suggested a technique for neutrons, but it turns out that neutrons are not suitable here.)
Hi Sofia,
Regarding the use or otherwise of neutrons for an HB&T setup, and assuming you're not trying to measure astronomical phenomena, how far apart would you need the detectors to be? How slow should the neutrons be? Even slow neutrons can move quite a distance in a little less than 15 minutes.
A slow neutron is generally reckoned at less than 1 eV. Even a thermal neutron at about 0.025 eV has (according to Wikipedia) a speed of 2.2 km/sec.
So for a lifetime of just under about 880 secs (depending on whether it’s measured by the bottle method or the beam method, as discussed in next month’s Scientific American; earlier article linked below), even a slow neutron should be able to travel almost 2000 km.
So would you still eliminate neutrons from consideration?
Regards - Paul
https://en.wikipedia.org/wiki/Neutron_temperature
http://www.scientificamerican.com/article/neutron-lifetime-mystery-new-physics/
Dear Paul,
Thank you for the references and for the calculi. The article in Wikipedia is known to me and the 2nd I read it and saw the picture - again thank you. Now, 2000km is excellent, 2.2km/sec is also excellent, but I don't see how the setup can be realized. Who can build a pipe as long as 2000km for the neutrons? This is one of the problems.
In the picture in the 2nd reference, I see a huge pipe. Is there where the neutrons travel? If yes, this is the problem, as I said, how to build such a long pipe. A technique is necessary for reflecting the particles repeatedly between two mirrors.
With kind regards,
Sofia
The Hanbury-Brown-Twiss experiment was first done with photons at all and since been done with other kinds of bosons. There's nothing particular with photons, anymore, beyond the historical fact that how to deal with photons was mastered earlier in time.
It's, also, been done with fermions: http://www.nature.com/nature/journal/v445/n7126/full/nature05513.html
https://tel.archives-ouvertes.fr/tel-00168946/document
with cold atoms, for instance. It's actually useful to read the experimental papers, in order to understand what ``long distance'' means and, in general, what are the systematic effects. While they are non-trivial, it is known how to take them into account. The thesis goes into considerable detail.
Cf. also here: http://science.sciencemag.org/content/284/5412/296
here
http://science.sciencemag.org/content/284/5412/296
for electrons
and many, many, more papers. Suffice to search for hanbury brown twiss fermions
and sort out the most relevant ones.
Dear Stam,
You are very kind. I browsed extensively in Internet and electronic archives. There is plenty of experiments indeed, and those you mention are known to me. But, it's not exactly the anti-bunching that interests me, but the 2-particle interference pattern created by the anti-symmetric wave-function, i.e. in two close detectors I won't get two fermions at once, if the detectors are some more distance yes I will get two fermions at once, more distance and again I'll get no two fermions at once, and so on.
This is why I stress that the configuration of the experiment has to be as in the attached picture. What I need is indeed intense, monochromatic sources and the clear pattern is obtained at big distances from the sources - see my exchange of comments with Paul Ellis.
Well, experiments as I am interested in, I didn't see that were done. People are glad to get the anti-bunching.
From the experiments described it's possible to deduce the interference pattern, that shows that it's fermions that are interfering, not bosons, that's the point of the experiments.
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