Poor man's double slit etc. setup

[Blue Scallop]

Hi, what is the cheapest double slit experiment setup or others where quantum state like qubits are isolated and can be experimented upon?

I saw the following in the net. It has a double slit inside the tube and the output is displayed on a monitor. I guess (not sure) it costs only $200. Has anyone seen this. What is it?

What others like it. Thanks.

 

[Trollfaz]

I saw this in Dean Radins video

 

[Blue Scallop]

When I mention poor man.. I didn't mean homeless.. it only means lost cost..

What is the lowest cost of double experimental setup commercially available?

And if you will build one in your own lab.. do you need to make it emit one photon or one electron at a time.. because if you just shine lights in the slits.. there are interference patterns too but they are just classical...

Also must the tube be totally enclosed.. so all double slit experiments use totally enclosed box? Are the detectors outside exposed to the air or must detector be *inside* the enclosed box too? I'm thinking if decoherence from the environment can affect the result if the detector is outside the box... (?)

 

[Vanadium 50]

You have not defined what you want to do very precisely. Consequently, nobody can tell us how much it will cost. You might think about explaining exactly what it is you want to do.

 

[Blue Scallop]

You have not defined what you want to do very precisely. Consequently, nobody can tell us how much it will cost. You might think about explaining exactly what it is you want to do.

I just want to own a quantum device where the photon or particle is in superposition of entering the left and right slit. or perhaps there are commercial Stern-Gerlach devices too? Or perhaps there is already a common household object that can display such isolated superposition (of course all molecules and atoms have superposition but need a single particle isolated that can display it). Just want to have a lab with one quantum device for experiments.

 

[ZapperZ]

Er... get a cheap glass slide, put it over a candle flame for a few seconds until you get soot covering all over it. Then get a sharp blade, and scribe two straight lines very close to each other on the slide that has the soot. Then get a cheap laser pointer, and voila! You have a double-slit setup!

I'd be surprise if this whole thing (including the laser pointer) costs more than $50.

Zz.

 

[Blue Scallop]

Er... get a cheap glass slide, put it over a candle flame for a few seconds until you get soot covering all over it. Then get a sharp blade, and scribe two straight lines very close to each other on the slide that has the soot. Then get a cheap laser pointer, and voila! You have a double-slit setup!

I'd be surprise if this whole thing (including the laser pointer) costs more than $50.

Zz.

but isn't the laser pointer acting like a classical source of light.. or do you mean it can do one photon at a time that can interfere with itself?

 

[ZapperZ]

but isn't the laser pointer acting like a classical source or light.. or do you mean it can do one photon at a time that can interfere with itself?

The interference pattern that you know and love is the result of single-photon interference. It doesn't matter if it comes from a single-photon source, or if it comes from a laser pointer.

Zz.

 

[Blue Scallop]

The interference pattern that you know and love is the result of single-photon interference. It doesn't matter if it comes from a single-photon source, or if it comes from a laser pointer.

Zz.

you mean a laser pointer emits single-photon at a time very fast.. what if one uses a powerfull small flashlight?

 

[vanhees71]

I guess a hole put in a sheet of paper with a needle + a laser pointer is also sufficient, and it gives a more interesting Bessel function as a refraction pattern . I once had a very cheap laser pointer, where they even delivered some gratings to play with. At the end it wasn't that cheap since it was pretty quickly not working anymore, but that's another topic...

 

[ZapperZ]

you mean a laser pointer emits single-photon at a time very fast.. what if one uses a powerfull small flashlight?

I think you still do not have a good grasp of even the CLASSICAL idea of interference.

A "small flashlight", is often NOT a monochromatic light source. Why do you think these demonstrations of interference, diffraction, etc. use a monochromatic light source?

I suggest that before dealing with the 'quantum' picture, you might want to try and understand the classical picture first.

Zz.

 

[vanhees71]

you mean a laser pointer emits single-photon at a time very fast.. what if one uses a powerfull small flashlight?

No, a laser pointer emits coherent states. To make true single-photon states is not that easy. Even a very much dimmed laser doesn't procude single-photon Fock states but rather coherent states which are dominated by the vacuum state.

One way to make true single-photon states is to use a laser and a BBO crystal to create entangled photon pairs. Then you can use one of the photons in each pair to trigger for the other photon ("heralded photon source"). I'm not sure, how much such a setup costs nowadays.

 

[Blue Scallop]

I guess a hole put in a sheet of paper with a needle + a laser pointer is also sufficient, and it gives a more interesting Bessel function as a refraction pattern . I once had a very cheap laser pointer, where they even delivered some gratings to play with. At the end it wasn't that cheap since it was pretty quickly not working anymore, but that's another topic...

In the slits.. how do you put a small camera (etc.) that can make it see which path.. and make the laser pointer interference pattern disappear?

 

[Blue Scallop]

I think you still do not have a good grasp of even the CLASSICAL idea of interference.

A "small flashlight", is often NOT a monochromatic light source. Why do you think these demonstrations of interference, diffraction, etc. use a monochromatic light source?

I suggest that before dealing with the 'quantum' picture, you might want to try and understand the classical picture first.

Zz.

I know a flashlight can't be used because it is just a classical source. About the laser.. I thought only one photon at a time source can produce the effect where if you try to peek which slit the photon passes thru, the pattern disappears.. how can you do the peeking for monochromatic light source? (I know the peeking can't be done for flashlight)..

 

[ZapperZ]

In the slits.. how do you put a small camera (etc.) that can make it see which path.. and make the laser pointer interference pattern disappear?

You are going to be sadly disappointed when I tell you that IF your intention is to test out a "which-way" experiment using a single-slit setup, then you'll never accomplish it. It is not THAT easy especially when you have to now consider a photon detector.

Most, if not all, which-way experiments use an "interferometer" setup (look it up), not a photon "double slit" setup. This is a lot more elaborate because it requires more optical equipment than I think you are even aware of.

Zz.

 

[ZapperZ]

I know a flashlight can't be used because it is just a classical source. About the laser.. I thought only one photon at a time source can produce the effect where if you try to peek which slit the photon passes thru, the pattern disappears.. how can you do the peeking for monochromatic light source? (I know the peeking can't be done for flashlight)..

A flashlight can't be used NOT because it is a "classical source". It can't be used because it pumps out a whole spectrum of light! A laser is a monochromatic source, i.e. it is predominantly a single-wavelength light source!

You get interference patterns with the flashlight, but because it has so many wavelengths in the light, the interference patterns "interfere" with each other and causing them to wash out!

There's a more fundamental level of understanding here that you still do not have. You need to learn how to crawl first before attempting your first Olympic sprint.

Zz.

 

[Blue Scallop]

You are going to be sadly disappointed when I tell you that IF your intention is to test out a "which-way" experiment using a single-slit setup, then you'll never accomplish it. It is not THAT easy especially when you have to now consider a photon detector.

Most, if not all, which-way experiments use an "interferometer" setup (look it up), not a photon "double slit" setup. This is a lot more elaborate because it requires more optical equipment than I think you are even aware of.

Zz.

But in the following.. it uses one photon a time using double slit.. it doesn't mention about interferometer...
http://www.animations.physics.unsw.edu.au/jw/light/youngs-experiment-single-photons.html

 

[ZapperZ]

But in the following.. it uses one photon a time using double slit.. it doesn't mention about interferometer...
http://www.animations.physics.unsw.edu.au/jw/light/youngs-experiment-single-photons.html

You really don't understand a lot of these things, do you?

If you look carefully at the experiment, you should notice that:

1. They have a "single-photon" source, which you do not have

2. They do NOT have a way to determine which way the photon passes through the double-slit. All they can do is close one slit.

Besides, if you are convinced that this is what you need, then why not just copy it (good luck with keeping this under budget).

For your information, my students have to do a similar experiment in their labs, so I know this type of setup very well.

What about my suggestion that you go back and study classical interference first to really understand the phenomenon? Or is understanding the physics here isn't what you wish to do?

Zz.

 

[Blue Scallop]

You really don't understand a lot of these things, do you?

If you look carefully at the experiment, you should notice that:

1. They have a "single-photon" source, which you do not have

2. They do NOT have a way to determine which way the photon passes through the double-slit. All they can do is close one slit.

Besides, if you are convinced that this is what you need, then why not just copy it (good luck with keeping this under budget).

For your information, my students have to do a similar experiment in their labs, so I know this type of setup very well.

What about my suggestion that you go back and study classical interference first to really understand the phenomenon? Or is understanding the physics here isn't what you wish to do?

Zz.

So universities and schools have this device. I wonder how much it costs. In my country.. not a single school has it. That's why I planned to purchase one so at least there is one in my country. Of course after I own one.. I'll be more motivated to learn the physics of it all..

 

[Blue Scallop]

I live in asia in a poor country. the closest country is Hong Kong or Singapore.. does anyone know if any university at HK or Singapore have a double slit single photon or interferometer setup that the public can take a peek? How about the science museums in HK or Singapore.. have you seen them? Anyone living in these countries?

About double slit single photon at a time experiment where "They do NOT have a way to determine which way the photon passes through the double-slit. All they can do is close one slit.".. you mean in the Interferometer setup.. it can determine which way? what light source does this interferometer have? laser or photon?

I know more questions and I have to ask in the General Physics forum since the above may not be quantum related question (?)..

 

[zonde]

In the slits.. how do you put a small camera (etc.) that can make it see which path.. and make the laser pointer interference pattern disappear?

Look at this DIY experiment.

 

[zonde]

Here are links to another DIY experiment. It is more expensive and sophisticated but, hey, it is observing entanglement.
Vanadium 50 was criticizing it but while in any DIY experiment you should expect a solid dose of wishful thinking I think he was too harsh. After all this DIY experiment was replicating 70 years old experiment done by professional scientists and published in respectable journal.

 

[zonde]

A direct observation that make me think "this can't be classical" is rather very trivial. Its large divergence of laser beam when it is partially blocked by a barrier versus small divergence of freely propagating laser beam. I don't see that this can be explained by Huygens principle (or bullet type particles).

 

[Blue Scallop]

Here are links to another DIY experiment. It is more expensive and sophisticated but, hey, it is observing entanglement.
Vanadium 50 was criticizing it but while in any DIY experiment you should expect a solid dose of wishful thinking I think he was too harsh. After all this DIY experiment was replicating 70 years old experiment done by professional scientists and published in respectable journal.

Can you think of the simplest setup that can make one test whether one can see superposition? The neuron can be in superposition of firing and not firing and decoherence is faster than neurons so we can't see superposition. But I just want to test it and see the result for myself... remember to see (or not to see) is to believe...

 

[Nugatory]

Can you think of the simplest setup that can make one test whether one can see superposition?

Superposition is much easier to observe. A laser and a few polarizing filters will do the trick: just compare what happens when you have two polarizer at right angles to one another with what happens when you insert a third filter at 45 degrees in between the first two. Adding the third filter increases the amount of transmitted light, a result that is very difficult to explain without superposition.

 

[vanhees71]

A direct observation that make me think "this can't be classical" is rather very trivial. Its large divergence of laser beam when it is partially blocked by a barrier versus small divergence of freely propagating laser beam. I don't see that this can be explained by Huygens principle (or bullet type particles).

Again: A "laser beam" is to a pretty good approximation a coherent state and not a single-photon state. It's well described as a classical electromagnetic wave, and I don't understand what you mean by that this example shows something non-classical. It's just diffraction at an edge, which has been fully understood (i.e., beyond Kirchhoff's approximate solution) by A. Sommerfeld, who was an expert in the theory of optical diffraction. His optics textbook is simply marvelous:

A. Sommerfeld, Lectures on Theoretical Physics, Vol. IV (Optics), Academic Press (1954)

Huygens's principle has to be used with a grain of salt. The mathematically fully correct version is found through using the retarede Green's function of the wave equation (in 3D space!),
$$G_{\text{ret}}(t,\vec{x})=\frac{1}{4 \pi |\vec{x}|} \delta \left (t-\frac{r}{c} \right), \quad r=|\vec{x}|.$$
For details, see Morse&Feshbach, Methods of theoretical physics, Vol. 1.

 

[zonde]

Again: A "laser beam" is to a pretty good approximation a coherent state and not a single-photon state. It's well described as a classical electromagnetic wave, and I don't understand what you mean by that this example shows something non-classical. It's just diffraction at an edge, which has been fully understood (i.e., beyond Kirchhoff's approximate solution) by A. Sommerfeld, who was an expert in the theory of optical diffraction.

I suppose I rather don't understand non-diffraction of freely propagating laser beam. Can you volunteer some explanation? I would like to understand what can be explained classically. I can start a new thread if it's more convenient.

 

[Vanadium 50]

while in any DIY experiment you should expect a solid dose of wishful thinking

But I just want to test it and see the result for myself..

It seems to me that Blue Scallop has a healthy scientific attitude, one that will not be satisfied by experimental noise plus "wishful thinking". Unfortunately, it's still not clear exactly what the OP is looking for, as well as a general confusion among participants in this thread on "entanglement" vs "superposition".

 

[DennisN]

Hi, @Blue Scallop, for very basic setups (and extremely cheap), please see my post here with various slit construction options, in the thread "Slit sizes needed for light diffraction".

 

[Blue Scallop]

If you don't see the 10 inside the globe above.. you are color blind.. similarly I want a quantum test akin to the following:

If the Stern-Gerlach would have spin up, the person would see "KEY"
If the Stern-Gerlach would have spin down, the person would see "BOARD".

I want to test if I or my friends can see both the superposition of up and down.. in other words if we can see both branches at same time or the "KEY BOARD" displayed instead of just KEY or BOARD. I want to confirm if the unitarity in qm is infallible and an unbroken law of nature. Also before projection (collapse or single outcome in MWI), it is supposed to be in superposition not just of up and down.. but in all angles located in configuration space.. I just to also test if I and my friends can see the superposition of all angles in configuration space. Remember wave functions are located in configuration space and not in physical space.

The point to do experiment is just to teach and verify for yourself. Why do your school has dynamo to demonstrate Maxwell's physics or others. It is to demonstrate to students.

So where to buy the Stern-Gerlach setup or can you think of a simpler setup that can do that above test. Nurgatory polarizer test is just a test where the result is the same even if one can see all branches at same time (this is what I want to demonstrate that it is not possible or unitarity in QM is a law set in stone). Thank you.

 

[Nugatory]

So where to buy the Stern-Gerlach setup

These aren't things that you can buy off the shelf. Each experimenter will have their own requirements so there's no possibility of building a standardized product and putting it in a catalog or up on Amazon. The building blocks (micrometers, polarizes, lenses, power supplies, oscilloscopes, electrical wire, timers, photodetectors, coincidence counters and other electronic bits, ...) are easily purchased, but it's up to the experimenter to figure out how to assemble these into an apparatus that they can use for whatever experiment they're conducting.

 

[Nugatory]

I want to test if I or my friends can see both the superposition of up and down..

Superpositions are pretty much by definition not something that can be seen. The best you can do is to come up with experiments like the polarizer one that I suggested, in which the results can only be easily explained by assuming the existence of a superimposed state.

 

[Vanadium 50]

Also, a single Stern-Gerlach experiment doesn't tell you anything about superposition.

I think you need to think more carefully - and this probably involves books - exactly what it is you want to show.

 

[Blue Scallop]

Also, a single Stern-Gerlach experiment doesn't tell you anything about superposition.

I think you need to think more carefully - and this probably involves books - exactly what it is you want to show.

In the double slit. There seems to be two kinds of superposition to wathc out for.. the superposition of going through left or right slit and the branches (the different spots in the detector) or the eigenvalues. Just want a device to prove there is no way to see the electron going via left and right at the same time. And there is no way to see all eigenvalues (screen positions) at all branches at the same time. Unitarity forbids them I know. But won't it be possible Unitarity can be distributed among Quantum sytem, Spacetime and Observer? Got this insight from Ken G when he suggested entanglement may be the norm and ordinary unentangled particles just a special case. Whatever even if he was wrong, just want to see it for myself Unitarity is 100% true all the time without any exception. If there is no a single double slit device anywhere in Hong Kong or Singapore.. I guess there is one in Japan, where?

Is there no Entanglement Museum anywhere in the world where you can see all these devices plus the Clauser, Aspect Bell devices? I'm just curious just like how kids want to see prism gets rainbows. Aren't you the public curious to see such actual devices?

 

[jtbell]

Its large divergence of laser beam when it is partially blocked by a barrier versus small divergence of freely propagating laser beam. I don't see that this can be explained by Huygens principle

"Far enough" away from a circular aperture (the technical term here is "Fraunhofer approximation"), the angular width θ of the central maximum of the diffraction pattern is proportional to λ/d where λ is the wavelength and d is the diameter of the aperture. This is well-established classical wave optics, see e.g. here:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp2.html#c2

The aperture that produces a laser beam is much wider than a pinhole, therefore light emerging from a laser aperture spreads much less than light emerging from a pinhole.

[added]

You get the same λ/d dependence in single-slit diffraction, which is easier to derive because one deals only with the transverse dimension across the slit, not along it. (With a circular aperture one has to deal with two dimensions, usually in polar coordinates, and introduce Bessel functions. ). A Google search for "single slit diffraction intensity derivation" brings up numerous mathematical derivations, of which this one is probably typical (I did this sort of thing in an intermediate optics course that I taught for many years):

https://courses.physics.ucsd.edu/2011/Winter/physics4d/files/Intensity in 1-slit pattern.pdf

Here's a graphical version involving phasors ("phase vectors") which one sometimes sees in first-year physics courses:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/sinint.html