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How is it even possible that a single photon can be isolated and "shot" through a slit? What tool or mechanism or setup allows such an incredible feat, especially since the photon has no mass?

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Have a look at this double slit single photon experiment:

dblslit single phot

In 2003, A. Weis and R. Wynands at the University of Bonn (Germany) designed a lecture demonstration experiment of single photon interference from a double slit. Light from a laser pointer was so strongly attenuated that at each instant there was only a single photon between the double slit and the detector. The diffracted light was recorded by a single photon imaging camera consisting of an image intensifier (multichannel plate, MCP) followed by phosphor screen and a CCD camera. When adding consecutive camera frames one sees the gradual appearance of the smooth classical interference pattern

Each dot on a camera frame appearing at (x,y) is the footprint of a single photon. The accumulation which gives the interference pattern is the probability density distribution for the quantum mechanical problem "photon impinging on two slits". The photon is "shot" at the two slits.

Photons show their particle nature by the (x,y) footprint at the camera frame, and their wave nature in the probability distribution . The classical electromagnetic wave which gives the same pattern as the single accumulation, is a confluence of an enormous number of photons.

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    $\begingroup$ It is important to emphasize that this should not be envisioned as photons traveling in particular trajectories and hitting the detectors at these specific locations. The EM field was interacting with the detectors everywhere and with Fermi's Golden Rule establish these "hits" with a certain probability. It is a didactic point since the OP asked about getting photons through a slit like a localized bullet which can't be done. $\endgroup$
    – Jan Bos
    Oct 9, 2016 at 8:34
  • $\begingroup$ @JanBos one hit is the footprint of one photon. The electric and magnetic field information is carried in the complex wave function of the photon whose Psi*Psi gives the probability of finding the footprint at (x,y) $\endgroup$
    – anna v
    Oct 9, 2016 at 8:41
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There is one very simple and very decisive experiment which proves the existence of photons beyond any doubt, and it involves exactly what the OP is asking about: shooting one photon at a time. You shoot photons at a half-silvered mirror and have two detectors, one for each path of the photon. Each time you shoot a photon, one of the detectors clicks. Either the photon got through or it was reflected. This proves light is made of photons: becuase if it were a wave, sometimes it would split in half and you would get clicks in both detectors.

This experiment has never been done. Oh, there are "similar" experiments involving something called parametric down-conversion which people claim amounts to exactly the same thing, but the actual experiment as described above has never been done. The reason is that there are no pea-shooters for photons. You can't shoot individual photons at will at a target.

I explain more about this in my blogpost, "There Are No Pea-Shooters For Photons".

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    $\begingroup$ At first glance P. Grangier, G. Rogers, and A. Aspect, Europhys. Lett. 1, 173 (1986) (and the full text available at physique.ens-cachan.fr/old/franges_photon/articles/… if nowhere else) appears to be exactly such an experiment. $\endgroup$ Oct 9, 2016 at 18:04
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    $\begingroup$ Okay, I looked at your reference. Isn't this one of the class of what I called "similar" experiments using two-photon states and correlation analyzers? These are admittedly very good experiments but they are not the pea-shooter by any means. $\endgroup$ Oct 9, 2016 at 18:14
  • $\begingroup$ The paper linked by @dmckee---ex-moderatorkitten doesn't use parametric down-conversion, but a two-step decay $4p^2 \, ^1S_0 \to 4s4p \, ^1P_1 \to 4s^2 \, ^1S_0$ in a Calcium atom. The two photons emitted in this process have different wavelengths and therefore can be separated. You might wonder why they don't use a single-photon decay right away; it's because they use the first photon as a gate for their detection, to decrease the influence of background light (which comes in all the time and not only right after the first photon). $\endgroup$
    – A. P.
    Dec 25, 2022 at 23:18
  • $\begingroup$ The absence of coincident clicks at the two detectors (antibunching) has also been measured with single-photon transitions, for the first time by H. J. Kimble, M. Dagenais, L. Mandel, Phys. Rev. Lett. 39 (1977). Since then, a lot of development has led to more and more efficient single-photon sources, see for example X.-L. Chu, S. Götzinger, V. Sandoghdar, Nat. Photonics 11 (2017). $\endgroup$
    – A. P.
    Dec 25, 2022 at 23:18
  • $\begingroup$ I acknowledged these anti-bunching experiments in the previous comments. But they are still very different from the simple experiment I described. There are no pea-shooters for photons. The experiment I descibed has never been done. $\endgroup$ Dec 26, 2022 at 3:39

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