Single particle single slit interference - question about the experiment

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Discussion Overview

The discussion revolves around the experimental setup of a single particle single slit interference experiment, specifically addressing how interference can occur when only one slit is open at a time. Participants explore the implications of path differences and the conditions under which interference is observed, referencing a specific experiment from the literature.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how a path difference is created if only one slit is open and how a photon could be said to come from either slit.
  • Another participant suggests that a phase shift in the paths may be used, proposing that a shutter could open each slit for a very short time, allowing for a delay in one path to create interference.
  • There is speculation about whether the delay should be equal to one wavelength or some multiple to maintain coherence for interference to occur.
  • Participants discuss the possibility of using optical control to manage the opening and closing of the slits in relation to the peaks of the light wave.
  • One participant posits that the interference pattern may not show up until a certain range of points where paths from both slits are possible, suggesting a visualization of the pattern at infinity.
  • There is a debate about whether the interference pattern would be visible on a screen placed at various distances from the slits, with one participant speculating that moving the screen closer might prevent the observation of an interference pattern.
  • Questions arise about the nature of the paths taken by the particles and whether something is physically traveling through all possible paths.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for interference to be observed and the implications of the experimental setup. There is no consensus on how the interference pattern evolves or the specifics of the path differences involved.

Contextual Notes

Participants acknowledge various assumptions about the experimental setup, including the timing of slit openings and the coherence of light paths, but these remain unresolved within the discussion.

San K
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Came across the below experiment, on Wikipedia, but don't understand how it was performed...

It was shown experimentally that:

in a double-slit system where only one slit was open at any time, interference was nonetheless observed provided the path difference was such that the detected photon could have come from either slit.

The experimental conditions were such that the photon density in the system was much less than unity.

Question: if only one slit is open --
how is the path difference created?
how could the photon have come from either slit?


Reference is:

Sillitto, R.M. and Wykes, Catherine (1972). "An interference experiment with light beams modulated in anti-phase by an electro-optic shutter". Physics Letters A 39 (4): 333–334. Bibcode 1972PhLA...39..333S. doi:10.1016/0375-9601(72)91015-8.
 
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Guessing from the title ...
It looks like they used a phase shift in the two paths. The thing to remember is that the photon paths are paths through space and time.

Try it this way, imagine a regular double slit experiment but with a shutter opening the two slits for a very short time.

Now let one slit be farther forward and let its shutter therefore open and close earlier so that both slits are never open at the same time.

Next, instead of moving one slit forward, instead put an equivalent delay I the path to that one slit. This is what It sounds like they did.
 
jambaugh said:
instead put an equivalent delay I the path to that one slit. This is what It sounds like they did.

Good guess jambaugh, thanks.

And is the delay equal to one wavelength (or some multiple) so that coherence is maintained between both the paths? to get interference
 
San K said:
Good guess jambaugh, thanks.

And is the delay equal to one wavelength (or some multiple) so that coherence is maintained between both the paths? to get interference

Possibly a quarter wavelength so one path's peak equals the other path's node. That would effect a shift in the interference pattern but you'd still get the double slit interference.

and again speculating from the title, the "slits" would be optically controlled, say with a laser so that as the peak passes it opens (or closes) each slit in turn.
 
jambaugh said:
Possibly a quarter wavelength so one path's peak equals the other path's node. That would effect a shift in the interference pattern but you'd still get the double slit interference.

well said...

jambaugh said:
and again speculating from the title, the "slits" would be optically controlled, say with a laser so that as the peak passes it opens (or closes) each slit in turn.

ok...open just in time to allow the peaks to pass through?
jambaugh said:
Now let one slit be farther forward and let its shutter therefore open and close earlier so that both slits are never open at the same time.

Next, instead of moving one slit forward, instead put an equivalent delay I the path to that one slit.
does the interference start (to happen/evolve) at the second/further/delayed slit?
 
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San K said:
ok...open just in time to allow the peaks to pass through?
Right.
does the interference start (to happen/evolve) at the second/further/delayed slit?
The interference pattern will not show up you've at a range of points where a path from both slits is possible. It is better, I think, to visualize the interference pattern at infinity, i.e. as a function of the angular position from the slits.
 
jambaugh said:
The interference pattern will not show up

?...we just agreed that there would a shifted interference pattern...

jambaugh said:
you've at a range of points where a path from both slits is possible. It is better, I think, to visualize the interference pattern at infinity, i.e. as a function of the angular position from the slits.

not sure what you are saying...however you have piqued the curiosity

do the range of points start post (or prior) the second/further/delayed slit?

if we were to place a screen after the second/further slit, we would see an interference pattern and as we move it backward the pattern would continue to show up

however if we moved the screen closer...and before the second slit (i.e. between the first and second slit)...i guess we would not see an interference pattern...right?

the actual experiment might not be done that way...however the above analysis can still be done, i guess...

does it not seem as if something is physically traveling through all the paths?
 
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