Buckyball Double Slit Experiment

[rodsika]

　

Buckyball Double Slit Experiment

I've been reading old archives here and even the FAQ and still not definite about the answer. It is said that a buckyball composed of 60 carbon atoms can still form interference pattern at the screen. It is not the complexity of the object but the fact that it is in superposition of states that makes it possible to interfere with itself. This means we must not imagine the 60 atoms as solid object in the double slit experiment because they are prepared in such a way that they are in superposition.

So a quantum particle is something that can do superposition. Does it mean that something that can do superposition lose any classical meaning of a particle. That is. If you can make the buckyball in superposition, then the atoms literally smear itself and lost any properties of atoms and become just waves?

Many physicists said to just consider them as quantum objects.. which is not exactly a particle or wave. But in the buckyball.. at some point, it has to travel in between the emitter and detector. So as quantum object, we mustn't imagine it as being a buckyball particle but as a quantum buckyball? But we know a buckyball is solid... as someone said "It consists of complex structure of 60 carbon atoms that in turn have complex structure of 6 electrons and ~12 nucleons that again in turn consist of 3 quarks. So it has 4 levels of structure (quarks-nucleons-nucleus-electron shells-molecule) consisting of different elementary particles with different charges and mass". So how can you imagine the buckyball as something that is not a buckyball. At what stage does it exhibits wave like property in between emitter and detector that makes it possible to interfere with itself??

Also it is said that the superposition is about superposition of eigenpositions and not superposition of positions. So we shouldn't think of it in terms of the buckyball duplicating themselves in all possible positions. But just superposition of virtual positions. But what does it mean the buckyball is in superposition? How can that be?

What exactly happens during superposition? Does the buckyball lose any sembrance of any classicality and the 4 levels of structure of quarks-nucleons-nucleus-electron shells-molecule dissolves into ghost-like state that is why it can still interfere with itself at the slit?

 

[Bill_K]

rodsika,

I can tell you're struggling with this idea, and probably whatever I say won't clear things up right away, but I'll try. Maybe it will sink in after awhile, so here goes.

There are not two separate worlds, quantum and classical. Everything is a quantum object under the proper conditions. Even something with internal structure like a buckyball. Even something complex like a cat. What proper conditions? Complete isolation and noninteraction with the rest of the world. A 'classical object' is constantly emitting and absorbing photons, so you can 'see' it, where it is, and which path it is following. A 'quantum object' is in total isolation as it travels from the emitter to the detector, consequently its position during that interval is unknown, which allows it to self-interfere. Under conditions of total isolation, you can do the two-slit experiment with asteroids.

 

[rodsika]

rodsika,

I can tell you're struggling with this idea, and probably whatever I say won't clear things up right away, but I'll try. Maybe it will sink in after awhile, so here goes.

There are not two separate worlds, quantum and classical. Everything is a quantum object under the proper conditions. Even something with internal structure like a buckyball. Even something complex like a cat. What proper conditions? Complete isolation and noninteraction with the rest of the world. A 'classical object' is constantly emitting and absorbing photons, so you can 'see' it, where it is, and which path it is following. A 'quantum object' is in total isolation as it travels from the emitter to the detector, consequently its position during that interval is unknown, which allows it to self-interfere. Under conditions of total isolation, you can do the two-slit experiment with asteroids.

You mentioned "its position during that interval is unknown, which allows it to self-interfere"... but unknown position won't by principle cause it to interfere. Unless during quantum isolation, the quantum object exits spacetime or something like that? What configuration of spacetime can occur to isolated quantum object such that it can appear in two places at once. Maybe we can solve the mystery by including both quantum and spacetime. Has anyone made such model or think along this line?

 

[ZapperZ]

You mentioned "its position during that interval is unknown, which allows it to self-interfere"... but unknown position won't by principle cause it to interfere. Unless during quantum isolation, the quantum object exits spacetime or something like that? What configuration of spacetime can occur to isolated quantum object such that it can appear in two places at once. Maybe we can solve the mystery by including both quantum and spacetime. Has anyone made such model or think along this line?

I think a lot of people don't realize that the double-slit experiment is another manifestation of the "Schrodinger Cat"-type scenario. Note that in this case, it is the superposition of paths, where you have an entity that has a situation where it can pass through both slits (dead and alive), but when you put a detector at one of the slits, it will then pass through one OR the other (dead OR alive).

To be able to detect such an effect, a quantum particle has to maintain coherence with other particles (or else the interference pattern will be washed out). One only needs to look at how these C60 molecules were prepared to perform such experiments.

On a side note, the largest particle to exhibit such quantum interference effect has just gotten bigger. The most recent report came this week when a molecule with 240 atoms (significantly larger than the 60 atoms in C60) has been shown to also produce interference effect.

http://www.nature.com/news/2011/110405/full/news.2011.210.html

Zz.

 

[rodsika]

I was reading about Delayed Choice Experiment a while ago.

It seems to suggest that it is not the detector put in the slit that can interfere with the wave function. Let's say in the 240 atom double slit experiment. You put a particle sensor behind the detector screen (Delayed choice style). You let the 240 atoms pass thru the slits. Then depending on how you turn on the sensor, you can affect the atoms back in time whether it will cause interference or not.

In Wheeler delayed choice experiment, photons can be affected billions of years ago.

We can treat photons as maybe a quantum object.

But now with 240 atoms, it should produce the same behavior.

Now between emission and detection. What do you think is happening to the 240 atoms?? It can even go back in time! (as do other pure quantum object).

It's like the 240 atoms lose their physicality. How else can it do superposition of paths and also go back in time? What is your thought of this? What do you think happen in between?

 

[ZapperZ]

Isn't this now a different question than what you posted originally? You are now delving into philosophy and trying to deal with superdeterminism of some kind. That is not what I was addressing, nor do I wish to go into such a thing.

Zz.

 

[Bill_K]

I was reading about Delayed Choice Experiment a while ago. It seems to suggest that it is not the detector put in the slit that can interfere with the wave function. It's like the 240 atoms lose their physicality. How else can it do superposition of paths and also go back in time? What is your thought of this? What do you think happen in between?

In Wheeler's version, the 'detector' is no longer a detector. What was previously a detector is now part of the experiment, and the state of the particle has become entangled with the state of the detector. A definite outcome is not determined until the final stage, when you 'open the box' and look at how the apparatus was configured. This is not philosophy and not backwards causality, it is just how quantum mechanics works.

It also does not make living observers out to be anything special. People are quantum objects just as much as anything else. Put the experiment plus yourself in a larger box, Box 2. Now when you observe the result, you have merely entangled yourself along with the apparatus, and remain in a mixed state along with it, until the box is opened and 'someone outside', i.e. the rest of the universe, opens Box 2 and observes you.

 

[rodsika]

In Wheeler's version, the 'detector' is no longer a detector. What was previously a detector is now part of the experiment, and the state of the particle has become entangled with the state of the detector. A definite outcome is not determined until the final stage, when you 'open the box' and look at how the apparatus was configured. This is not philosophy and not backwards causality, it is just how quantum mechanics works.

It also does not make living observers out to be anything special. People are quantum objects just as much as anything else. Put the experiment plus yourself in a larger box, Box 2. Now when you observe the result, you have merely entangled yourself along with the apparatus, and remain in a mixed state along with it, until the box is opened and 'someone outside', i.e. the rest of the universe, opens Box 2 and observes you.

In wheeler delayed choice experiment that involves quasar light source and Galactic lens interferometer, where putting a detector at position A or B can affect produce whether there is interference pattern or not. I wonder if this is like the double slit experiment? If it's related. Then rather than believing photons emission were affected billions of years back in time (which is clearly ridiculous), perhaps the photons don't really take any path. Perhaps it is just the wave that travels around the galactic lens. Then the photons are just local effects in the detector.

But how do you take the analogy to 240 atoms quantum object. Maybe when quantum object is put in coherent state and when isolated. It totally lose any particle quality to it and become just like the waves in the Wheeler delayed choice galactic lens interferometer experiment?

 

[alxm]

Nothing special happens during superposition. The buckyball (or whatever you like) is not in a coherent state. There's a difference between the de Broglie wavelength being measurable (under some very specific experimental conditions) and the superposition being significant. Atoms are always in motion, and the de Broglie wavelength here is so short relative the scale of that motion, that you can regard the motion of even a single atom to be almost entirely classical.

The de Broglie wavelength of a buckyball is only about 2% of the interatomic distance in the molecule and less than 1/300th the size of the molecule as a whole. The atoms still have quite definite positions from the chemical point of view. If you were to label them somehow (perhaps using different carbon isotopes), you would not find any of the atoms switching places with the other ones. The position of an atom isn't ever really viewed as having specific exact coordinates. Chemistry defines its position in relation to the neighboring atoms. Which is natural, since they don't have definite locations, but also because even classically they'd still be in motion at all nonzero temperatures. And in that 'chemical' definition of where an atom is, these superpositions change nothing.

The only thing known to move quantum-mechanically to a chemically-meaningful extent, under ordinary conditions, are hydrogen atoms.

There is no binary relationship saying things behave either classically or quantum-mechanically. As mass increases, things start behaving increasingly classically. The fact that you can measure quantum behavior of large objects doesn't mean it's required to describe their properties accurately. In fact, most if not all real quantum-mechanical calculations on properties of buckyballs treat the nuclei as if they're classical or semi-classical, as do quantum-chemical and solid-state calculations in general.

 

[rodsika]

I was also thinking the buckyball remains whole in between the emitter and detector because quarks can't be separated. Now the most important question. If the buckyball remains whole, how does it interfere with itself when you do one at a time buckyball double slit experiment?

Nothing special happens during superposition. The buckyball (or whatever you like) is not in a coherent state. There's a difference between the de Broglie wavelength being measurable (under some very specific experimental conditions) and the superposition being significant. Atoms are always in motion, and the de Broglie wavelength here is so short relative the scale of that motion, that you can regard the motion of even a single atom to be almost entirely classical.

The de Broglie wavelength of a buckyball is only about 2% of the interatomic distance in the molecule and less than 1/300th the size of the molecule as a whole. The atoms still have quite definite positions from the chemical point of view. If you were to label them somehow (perhaps using different carbon isotopes), you would not find any of the atoms switching places with the other ones. The position of an atom isn't ever really viewed as having specific exact coordinates. Chemistry defines its position in relation to the neighboring atoms. Which is natural, since they don't have definite locations, but also because even classically they'd still be in motion at all nonzero temperatures. And in that 'chemical' definition of where an atom is, these superpositions change nothing.

The only thing known to move quantum-mechanically to a chemically-meaningful extent, under ordinary conditions, are hydrogen atoms.

There is no binary relationship saying things behave either classically or quantum-mechanically. As mass increases, things start behaving increasingly classically. The fact that you can measure quantum behavior of large objects doesn't mean it's required to describe their properties accurately. In fact, most if not all real quantum-mechanical calculations on properties of buckyballs treat the nuclei as if they're classical or semi-classical, as do quantum-chemical and solid-state calculations in general.

 

[rodsika]

Come on. We candetermine what happens in*between. And it's not philosophy. In the past, we only have electron or photon and it's not inconceivable that they can shapeshift into wave and particle. But with Buckyball composed of not just 60 but 430 atoms. We are sure it doesn't appear as ghost halfway because quarks can't be separated. So at least some aspect of Copenhagen is debunked that in the middle it is all a wave of possibility and a particle only appear during collapse... we surely can't accept that the buckyball reappears at the detector.
*
Also we have many interpretations but these are only for laymen and to get them interested in QM. Here we can debunk Many World because it is silly. It's only a simple problem about what happens in between and they are proposing a multiplicity of worlds. Bohmian seems to be promising but QFT debunks it because Bohmians being fixed particles can't form creation/annihilation. Bohmian mechanics is also not lorentz invariantz.
*
So with Copenhagen, Many worlds, Bohmian debunked and eliminated.
*
Let's figure out a more rational explanation of what happens. Perhaps each of the particle in the 430 atoms can form waves and the whole atom is in coherent state and it is moving in between the emitter and detector such that it can cause interference? Pls. give a better description what happens rationally.

 

[alxm]

I was also thinking the buckyball remains whole in between the emitter and detector because quarks can't be separated.

You don't need that argument. Elementary particles such as electrons display interference patterns as well.

Now the most important question. If the buckyball remains whole, how does it interfere with itself when you do one at a time buckyball double slit experiment?

Because the buckyball as a whole is acting like a wave. Just because it's a composite object doesn't mean it's splitting apart here. You never detect half a buckyball anywhere. You either detect everything or nothing (to an extremely high probability). If you want to model the overall wave function of the thing in terms of the individual particles, you can do that too, but you'll end up with the same result.

 

[alxm]

In the past, we only have electron or photon and it's not inconceivable that they can shapeshift into wave and particle.

They're not 'shapeshifting' since they're neither particles or waves. Quantum mechanics doesn't distinguish between something 'acting like a particle' and 'acting like a wave', so why should we?

 

[rodsika]

alxm (Science Advisor) said:

"Nothing special happens during superposition. The buckyball (or whatever you like) is not in a coherent state"

ZapperZ (PF Mentor) said:

To be able to detect such an effect, a quantum particle has to maintain coherence with other particles (or else the interference pattern will be washed out). One only needs to look at how these C60 molecules were prepared to perform such experiments.alxm said buckyball is not in coherent state even in interference experiment while ZapperZ mentioned it has to maintain coherence or else there will be no inteference. How can they be in total conflict each other? If they are normal PF contributer. It is ok. But one is a science advisor, the other is a PF Mentor. I hope some other expert can resolve the conflict as this confuses me for many hours analyzing it already. Thanks.

 

[alxm]

How can they be in total conflict each other? If they are normal PF contributer. It is ok. But one is a science advisor, the other is a PF Mentor. I hope some other expert can resolve the conflict as this confuses me for many hours analyzing it already.

Maybe before you spend 'many hours' on it next time, you should first check whether there actually exists a conflict.
Five minutes with Google could've informed you that http://en.wikipedia.org/wiki/Coherence_%28physics%29" aren't the same thing.

 

[rodsika]

Nothing special happens during superposition. The buckyball (or whatever you like) is not in a coherent state. There's a difference between the de Broglie wavelength being measurable (under some very specific experimental conditions) and the superposition being significant. Atoms are always in motion, and the de Broglie wavelength here is so short relative the scale of that motion, that you can regard the motion of even a single atom to be almost entirely classical.

*

Going back to this coherent state versus coherence. I spent another hour reading many web sites what is a coherent state (i already know what is coherence). But I'm still not sure why you have to mention coherent state here. We are discussing about buckyball in a double slit experiment. Here we are talking about the buckyball 60 atom particles being in coherence. Now why did you have to mention about coherent state. Are you talking of normal buckyball or a specially prepared one put in a superposition?

Also you mentioned about that nothing special happens during superposition. Well. If that is so, how come other physicists believe superposition itself can spawn Many Worlds?

*

Because the buckyball as a whole is acting like a wave. Just because it's a composite object doesn't mean it's splitting apart here. You never detect half a buckyball anywhere. You either detect everything or nothing (to an extremely high probability). If you want to model the overall wave function of the thing in terms of the individual particles, you can do that too, but you'll end up with the same result.

But don't forget Born said that before the wave function collapse, the wave just is a wave of possibility. So position of the particle is undefined. You can't assume there is a classical trajectory because if that is so, you need something to manuever the particle to the slits.

 

[ExecNight]

Well one can do this experiment at home :)

Get a dice, put it in a cup and shake it. Afterwards close it on the ground. There you have your wavefunction and superposition. It can be any results now, if you use the right mirroring inside the cup, the mirrors will show on a screen outside the cup that the dice show every possible 6 results.

Now remove the cup, and there you have your wavefunction collapsed. It just shows 5.

Anyway i have green and yellow eyes, but when people look they are brown ;(

--

No offense intended just very bored at work.

 

[ZapperZ]

Well one can do this experiment at home :)

Get a dice, put it in a cup and shake it. Afterwards close it on the ground. There you have your wavefunction and superposition. It can be any results now, if you use the right mirroring inside the cup, the mirrors will show on a screen outside the cup that the dice show every possible 6 results.

Now remove the cup, and there you have your wavefunction collapsed. It just shows 5.

Anyway i have green and yellow eyes, but when people look they are brown ;(

--

No offense intended just very bored at work.

This isn't superposition, and it highlights why the fact that the wavefunction is NOT simply a reflection our ignorance of the system before a measurement. If it is, then it wouldn't have been THAT mysterious since we didn't have this issue with classical statistical mechanics!

Note that our observations from Chemistry, and the various Schrodinger Cat-type experiments, clearly indicates effects that came directly out of the superposition principle. These are NOT present in classical statistical mechanics, i.e. that dice that you haven't seen yet doesn't produce any physical effect due to your lack of knowledge of what it has turned up. In QM, it does! The existence of the coherence gap in the SQUID experiments from Delft/Stony Brook is one such example.

You need to be careful that your boredom at work doesn't cause you to make posts that violate the PF Rules that you had agreed to.

Zz.

 

[ExecNight]

Can you explain how Superconducting quantum interference devices. Are different than other observations?

How is this experiment special? Coherence gap?

 

[cayley]

at nano level particles are treated as waves...according to the quantum concept it gives an interfearence pattern.

 

[Dmitry67]

it really has nothing with a SCALE.

 

[eloheim]

Note that our observations from Chemistry, and the various Schrodinger Cat-type experiments, clearly indicates effects that came directly out of the superposition principle. These are NOT present in classical statistical mechanics, i.e. that dice that you haven't seen yet doesn't produce any physical effect due to your lack of knowledge of what it has turned up. In QM, it does! The existence of the coherence gap in the SQUID experiments from Delft/Stony Brook is one such example.

Hey please tell me if I'm pushing too far out from the intention of this thread, but I honestly don't know enough to be able to tell if the following is relevant or not.

I looked up the SQUID experiments you mentioned in the quoted post, Zz [e.g. http://www1.amherst.edu/~jrfriedman/Scientific American/scientific-american edited.html ]. One of the other google results, though, is what my post is about. It's a paper that originally appeared (apparently) in the journal Physics Letters A. Here's some info:

Why SQUID experiments can rule out non-invasive measurability

Andrew Elby; Sara Foster

Department of Physics, University of California at Berkeley, Berkeley, CA 94720, USA

Subfaculty of Philosophy, 10 Merton Street, University of Oxford, Oxford OX1 4JJ, UK
Received 25 February 1992;
accepted 13 April 1992
Communicated by J.P. Vigier
Available online 17 September 2002.

Abstract

From macrorealism and non-invasive measurability (NIM), Leggett and Garg derive inequalities that contradict QM's predictions for SQUIDs. We derive those inequalities from NIM and a “realism” assumption weaker than macrorealism. If Tesche's null-result measurements violate those inequalities, our derivation suggests that NIM is the “culprit” and must be renounced.

Unfortunately I have no access to this database, so all I know is what we see in the abstract. Can anyone explain for me what it is saying? I guess the phrase, "contradict QM's predictions for SQUIDs," caught my eye particularly, especially in light of the article's adjacents (:tongue2:) to issues germane to the thread at hand, such as 'Macro vs. micro,' 'quantum measurement,' 'realism,' etc.

Thanks to everyone for their time.

[And as a tiny side note: I know this thread probably borders on becoming overly 'philosophically-inclined' in places, and I'd bet there's some stuff in here that makes the seasoned physicist squirm in his/her seat. But as a lay-person just interested in this stuff from a non-professional perspective, these posts have opened up at least a couple new 'paths of inquiry' for me to pursue in the future, for which I'm grateful. Also, I believe that, although understandably irritating, having these same common sense-based misconceptions, stated in different ways, dismantled again and again by all different knowledgeable individuals, actually does have value, as each time the 'questions' will be stated a mite bit differently, and the answers are given from (even if only slightly) distinct perspectives. {Edit addition: Said 'value' being due to the fact that dispelling life-long held assumptions about the ways of the world can't be simply 'reasoned away' on a single occasion or two (IME, at least); it takes something more akin to a continuous bludgeoning of the offending principles, in all their myriad permutated manifestations, over an extended period of time!} I guess this is basically just a (humble ) plead to the moderators for leniency when dealing with discussions where it appears that 'progress' may be being made. (The whole 'Dice game' post, though, not-withstanding...lol, sorry ExecNight there's no defending whatever that was ...)]

Okay peace for real this time!

 

[billschnieder]

It is said that a buckyball composed of 60 carbon atoms can still form interference pattern at the screen

...

What exactly happens during superposition? Does the buckyball lose any sembrance of any classicality and the 4 levels of structure of quarks-nucleons-nucleus-electron shells-molecule dissolves into ghost-like state that is why it can still interfere with itself at the slit?

Probably nitpicking but a buckyball does not form an interference pattern. The buckyball forms a single dot on the screen. Many different buckyballs form different spots on the screen which together form an interference pattern.