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Quantum home experiments

  1. Jan 16, 2008 #1
    Hi all,

    I was wondering if there are any quantum experiments that I can perform at home?
    I am talking about basic experiments by using equipments that I can purchase easily on the market - like polarized films, laser pointer etc....and how can I construct those experiments?

    Thanks in advance...
  2. jcsd
  3. Jan 17, 2008 #2
    One you could perform very easily and cheaply. Get three polarizers. Place them in sequence - one at 0 degrees, one at 45 degrees, and the third at 90 degrees. Shine a flash light through them. The light will end up very dim on the other end but visible. Now remove the middle (45 degree) polarizer and shine light through again. No light will get through! Now insert the 45 degree polarizer and remove the 90 degree polarizer. Light will get through again, and it will be more intense than when there were three polarizers! Nuts, huh! :)

    Now what should really rock your world is that if you'd inserted the final polarizer after the photon had already passed through the other two, the result would be the same as if the polarizer had always been there...
  4. Jan 17, 2008 #3
    First paragraph is fine and a good example.
    For polar filters just look for a couple of cheap polarizing sunglasses (not as easy to find as they had been but the polar type can still be found in some $1 stores); break them up and you have four filters to play with.

    But there is nothing odd to "rock your world" about inserting the last filter and how it treats light that departed the 2nd filter before placing it. - Plus no one can do that test at home anyway.

    Just remember that any experiment you can “do at home” is at best a macro simulation of a quantum example. You simple cannot do a real quantum experiment unless you can reliablley control and count a single quantum (photons or electron). That is beyond anything you can do “at home”.

    Remember these types of experiments existed before the quantum science and were successfully answered by classical views and interpretations for LIGHT. But when the ability to perform these tests in dim enough light that one could be sure the tests were done on a particle by particle (or quantum by quantum) do the classical explanations no longer hold up for quantum tests. Only then did a need for a quantum explanation become needed.

    Understanding that, if you are willing to try a tough home example of a quantum test that is not easy or cheap look, at page 92 of the May 2007 Scientific American for “quantum Erasing in the Home”.
    Not a real “proof” by any means but with a bit of work could be fun.
  5. Jan 17, 2008 #4
    It's a similar idea to Wheeler's Delayed Choice experiment, and I think it's pretty astounding, considering that light is made of photons and is not a classical wave. And, no, sadly, it cannot be done at home.
  6. Jan 17, 2008 #5
    OMG!!! Sounds like fun, I will have to read that one!

    Don't try this one it is just trouble:

    Well, maybe you could do it, but I have yet to succeed convincingly.
    Last edited by a moderator: Sep 25, 2014
  7. Jan 17, 2008 #6
    I have done that one and it is much easier to show this diffraction than “Quantum Erasing in the Home”.
    I used a carpenter’s laser level for the light beam.
    Use two playing cards face to face with thin pieces of cardboard separating them top and bottom. Light only goes through the small gap between them after taping a paper barrier on the outside sides of the cards.
    The beam going through the slit widened very noticeably.
    I just tossed it together using masking tape; took about 20 minutes with most of the time getting things to line up straight.
    But, again that is a classical expectation for light, well defined in the 1800’s.
    Last edited by a moderator: Sep 25, 2014
  8. Jan 17, 2008 #7
    Ok, here's another one ( but, sadly, also explicable classicly ).It's a cheap and easy two-slit job.
    You need an assistant to help.
    All you two need are two bright, sunny windows A and B on the same wall into an otherwise blacked-out room and four opaque boards e.g. pieces of wood.

    *1* Completely cover window A with two completely opaque boards.
    Mostly cover window B with two boards leaving a small vertical crack between the boards.
    You get single crack of light on wall.
    (Note that you really need two boards for each window rather than use one edge of the window, because of possible reflections from the window/wall recesses.)

    *2* Now close B completely and open a vertical crack on A.
    Again, you get single crack of light on wall.

    *3* Now open a crack on both A and on B.

    I did this by accident when I was a kid when shuttering out the sunlight from the telly but didn't know why it did that.
    Now we know! Note that the room wasn't blacked out very well at all but it still worked.
    I guess the distance between the cracks should be less ( significantly less?? ) than the distance from the windows to the opposite wall.

    Interestingly, I tried to duplicate this on a smaller scale with a torch shining into a shoebox with cardboard barrier with slits, but it 'didn't work'. I assume sunlight works well because it's so bright, and bonus!- you are actually standing in your own experiment!!!
  9. Jan 17, 2008 #8


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    This is quite cool, but I'm not really convinced that it is a proper quantum physics experiment, as it is all consistent with the classical theory of light as a wave. I suppose that you would need to detect the photons one a time to really see the quantum effects (I have no idea how you could do that).
  10. Jan 17, 2008 #9
    True true, but if one accepts the premise that light is made of particles then the results are astounding.

    I mean, honestly, you're not going to prove Heisenberg's Uncertainty Principle for under $1000. At least it's still less expensive than proving relativity! :)

    I wonder if you could rig an old tube TV to use its electron gun to do Young's electron double slit.

    Or you could just cut a coin in half the long way and put them in envelopes and make the recipients open them miles apart to demonstrate entanglement.... KIDDING! :)
    Last edited: Jan 18, 2008
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