Macro Superposition: Does Size Matter?

[bhobba]

but I have another question superposition is just a statistical probability wave function. Is this correct and if someone could address some of my earlier and I know stupidly obvius questions for sci advisors.

Superposition is a consequence of the QM formalism, namely the states (actually the pure states - but we won't be that picky) form a vector space. It is related to probabilities by the so called Born rule that I will leave it to you to look up.

At an intuitive level the following is the best take I know on what QM is:
http://arxiv.org/pdf/quant-ph/0101012.pdf

Thanks
Bill

 

[batmanandjoker]

The vacuum removes the air, not the slits. If you remove the slits, it's no longer a double slit experiment. There exist no classically consistent accounts no matter who and what will say otherwise.

I honestly don't understand mauis last post. Anyways my question is hypothetical but does a larger object even though its entangled with the enviorment and collapsed displays a smaller superposition than smaller objects. I understand this is a hypothetical and both objects are collapsed. Any repsonse would be greatly appreciated.

Also so photons are the only particles that can display macro superposition without entanglment however atoms do not is this correct.

 

[ZapperZ]

I honestly don't understand mauis last post. Anyways my question is hypothetical but does a larger object even though its entangled with the enviorment and collapsed displays a smaller superposition than smaller objects. I understand this is a hypothetical and both objects are collapsed. Any repsonse would be greatly appreciated.

Also so photons are the only particles that can display macro superposition without entanglment however atoms do not is this correct.

Your questions are often very confusing. And I feel as if you are taking snippets of bits and pieces of information and sticking them together without really understanding the underlying principle.

First of all, you shouldn't use the word "entangled", because that has a specific meaning in QM. Please use something like "interaction".

Secondly, what is a "smaller superposition"? How are you quantifying the degree or magnitude of superposition here?

Lastly, what exactly do you mean by "macro superposition"? I see interference pattern from electrons every week (sometime, 3 days in a row when I'm making measurements). That has the same "size" as any interference pattern made by light. Is that what you consider as "macro superposition"? Someone has already mentioned about a 2-slit experiment using things as large as buckyballs, which are a lot larger than atoms. Are these not "macro" enough for you?

It is hard to know what you have already understood. For example, the often-repeated assertion of the preservation of coherence, and not size, as the most important factor, is this something that you've already understood? It is not clear if you have considering you never acknowledge it. Maybe this is something you should try to understand FIRST, because most, if not all, of your questions can be answered if you get this part. You also never acknowledge if you think there is still an "inconsistency" here with your understanding of interference pattern with light and electrons. So again, it is difficult to know if we are still rehashing the same issue, or if you've moved on to a different one.

Zz.

 

[DevilsAvocado]

I honestly don't understand mauis last post. Anyways my question is hypothetical but does a larger object even though its entangled with the enviorment and collapsed displays a smaller superposition than smaller objects. I understand this is a hypothetical and both objects are collapsed. Any repsonse would be greatly appreciated.

Also so photons are the only particles that can display macro superposition without entanglment however atoms do not is this correct.

There seems to be some confusion... I would recommend you, for simplicity, to exchange the technical word entanglement for disturbance, since entanglement could be a very delicate state between to two “twin particles”, which is lost in interaction with the environment. It could be a tricky thing to conceive that “entanglement destroys entanglement” (even if this actually happens)...

Regarding “the size/length of superposition”, I’m not sure what you are talking about, but I guess you mean the distance between the slits in the Double Slit Experiment (as one example), right? If that’s the case, then there’s a relation between the wavelength of the object and the distance between the slits and to the screen, in the standard interpretation (however there are other formulations of QM, as the path integral, which replaces a single trajectory over an infinity of possibilities, including a trip to Alpha Centauri and back!).

Photons (zero rest mass/no electric charge) are easier to “screen off” from disturbance/interaction in experiments, than as for example electrons, but the first experiment in the history of science to measure superposition in quantum states (spin) used silver atoms:

Stern–Gerlach experiment
https://www.youtube.com/watch?v=uqDlIgUDEIA


The experiment was performed in a vacuum so that the silver atoms could move in a straight trajectory without scattering. The really weird thing however, is that if you make this measurement in a sequence of three magnets, passing only one result/beam to the next, measuring the spin along the z --> x --> z axis, will still result in a 50/50 up/down after the last magnet! That’s because of QM superposition.

In QM we are dealing with a duality of waves/particles. As you know waves have a frequency, and can spread out, create interference, etc. This is obviously not possible for particles, which are localized.

The main reason you can use a laser on the wall in a classroom, to perform the Double Slit Experiment, is that the light from the laser is coherent and can be focused to a tight spot.

Coherent waves

Decoherent waves

Laser
https://www.youtube.com/watch?v=h7lhtHtKXIY


It is however possible to perform the Double Slit Experiment with ordinary sunlight, even if it requires a little bit more equipment (as Thomas Young did in 1803 when lasers were not available).

The Original Double Slit Experiment
https://www.youtube.com/watch?v=Iuv6hY6zsd0


QM is wonderful and strange and what puzzles many is the relation between the wavy nature (i.e. waves of probabilities) and the localized particles we get in measurements. Maybe strangest of all is the Bose–Einstein condensate, where matter literally acts like a coherent wave...

 

[batmanandjoker]

bhobba kept using the word entangled but I think he meant interaction is this correct this is what confused me. I also understand the photon thing now. So it is the interaction with the external enviorment that collapses particles superposition in the macro world, does entanglement (which I do know what it is) have anything to do with this collapse or was I just using the incorrect termonolgie.

 

[bhobba]

bhobba kept using the word entangled but I think he meant interaction is this correct this is what confused me.

When particles interact that may become entangled or not - but interaction is required for entanglement - that, and if they are created that way to begin with, really are the only ways for them to be entangled:
http://en.wikipedia.org/wiki/Quantum_entanglement

Thanks
Bill

 

[DevilsAvocado]

So it is the interaction with the external enviorment that collapses particles superposition in the macro world,

Correct, it’s the interaction with the environment that disturbs the “macroscopic superposition” to collapse/decohere. Here’s an article on the fattest Schrödinger cats realized to date, an experiment performed on large organic molecules consisting of 430 atoms, in a coherent state where the matter waves are all in step. Here’s the experiment.

... I’ve always wonder what it takes to get an elephant (not in the room, but) in a coherent state ...

does entanglement (which I do know what it is) have anything to do with this collapse or was I just using the incorrect termonolgie.

Yes, that could be the case, but I can’t say if that’s the case in all situations. I leave that to the professional experts in this thread.

(If I don’t remember wrong, Roger Penrose has stated that the whole universe is/will be entangled?? And if this is correct, entanglement always causes collapse/decoherence... but I’m not sure...)

 

[batmanandjoker]

From what I understand decoherance causes particles to collapse IE remove their state of superposition is this correct

 

[bhobba]

From what I understand decoherance causes particles to collapse IE remove their state of superposition is this correct

It causes APPARENT collapse.

I will leave it up to you to investigate the difference.

Thanks
Bill

 

[batmanandjoker]

I really need help here what do you mean by APPARENT collapse can you be specific are you suggesting your not exactly sure that decoherence collapses wave functions IE superposition. Because this is contradicatry to your earlier posts. This is very confusing for me I don't even know where to begin INVESTIGATING whatever diffrence your talking about. Does decoherance cause wave function collapse or create the illusion that it does and everything is still in superposition. Any help would be greatly appreciated.

 

[bohm2]

This is true but how do you explain this

http://www.nature.com/news/2010/100317/full/news.2010.130.html

they detected superposition in a macro object could you please explain your perspective on this article. Thanks.

The experiment just demonstrates that QM is also a macroscopic phenomenon; that is, QM does not only apply at the micro level. While there is a superposition of states that is not the same thing as observation of an object at 2 places at once.

 

[batmanandjoker]

No. The double slit experiment has been carried out without isolating single electrons from their 'environment'(whatever that means quantum mechanically!) or isolating them from interacting with the slits(electrons somehow do not seem to care about interaction with the plate that houses the slits so no decoherence there).

http://physicsworld.com/cws/article/news/2013/mar/14/feynmans-double-slit-experiment-gets-a-makeoverBTW, if you want a real understanding of what is going on, a 'bare' decoherence theory will only get you half-way at most.

I feel that this is a false statement nowwhere in the article does it state that the electrons were not isolated from their enviorment it has already been refrenced by a sci advisor that electrons need to be in a vacuum to exhibit superposition. Can a sci advisor tell me if I am correct.

 

[audioloop]

The experiment just demonstrates that QM is also a macroscopic phenomenon; that is, QM does not only apply at the micro level. While there is a superposition of states that is not the same thing as observation of an object at 2 places at once.

have to be seen at at 10¹⁰ - 10 ²⁰ atoms.

 

[bhobba]

I really need help here what do you mean by APPARENT collapse can you be specific are you suggesting your not exactly sure that decoherence collapses wave functions IE superposition. Because this is contradicatry to your earlier posts. This is very confusing for me I don't even know where to begin INVESTIGATING whatever diffrence your talking about. Does decoherance cause wave function collapse or create the illusion that it does and everything is still in superposition. Any help would be greatly appreciated.

Apparent means observationaly its the same - but actual collapse is another matter.

The jig is up here - can't give any more detail without the math - it requires knowledge of the difference between proper and improper mixtures which requires considerably more background than you have. Here is the detail for future reference:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Thanks
Bill

 

[Maui]

I feel that this is a false statement nowwhere in the article does it state that the electrons were not isolated from their enviorment it has already been refrenced by a sci advisor that electrons need to be in a vacuum to exhibit superposition. Can a sci advisor tell me if I am correct.

I could be wrong about the vacuum but for different reasons not related to decoherence. The distances between the slits are extremely tight and you need electrons that travel unimpeded from the electron gun to the screen. That is why you want to remove the air so that a near perfect straight line is traversed.

As I said earlier, if environmentally induced decoherence had anything to do with the behavior in the double slit experiement, electrons would have decohered and collapsed upon interaction with the slits and interference would not have been observed. But it is. The above approach treats objects as if there were different levels of quantumness - classical quantumness not exlpained by quantum mechanics and regualr quantumness that is thoroughly explained by it. However accepting the premise leads to the conclusion that the slits must be made of that special classical quantumness and should therefore cause decoherence to the passing electrons at all times.

Btw you should not read these interpretational opinions like Gospel. There are quite a number of possible explanations and as of today no one knows which is right(not even the sci advisors ;) )

 

[batmanandjoker]

I could be wrong about the vacuum but for different reasons not related to decoherence. The distances between the slits are extremely tight and you need electrons that travel unimpeded from the electron gun to the screen. That is why you want to remove the air so that a near perfect straight line is traversed.

As I said earlier, if decoherence had anything to do with the behavior in the double slit experiement, electrons would have decohered and collapsed upon interaction with the slits and interference would not have been observed. But it is. The above approach treats objects as if there were different levels of quantumness - classical quantumness not exlpained by quantum mechanics and regualr quantumness that is thoroughly explained by it. However accepting the premise leads to the conclusion that the slits must be made of that special classical quantumness and should therefore cause decoherence to the passing electrons at all times.

Btw you should not read these interpretational opinions like Gospel. These are quite a number of possible explanations and as of today no one knows which is right(not even the sci advisors ;) )

Between a sci advisor and some random poster sorry but I prefer to listen to a sci advisor for all I know you might be one of those quantum spiritual types.

Anyways please please in lamen terms if you can distinguish or TRY to explain the diffrence between an observational collapse and an actual or mathematical collapse if that's what your implying. Can one mathematiclly determine collapse while at the same time observe collapse experimentally. Please you would help me a great deal see I suffer from obsessive compulsive disorder and the distortion of reality in my own mind created by my own ignorance of how some suggest the quantum world contradicts the macro classical world creates anxiety for me.

THE BASIC QUESTION IN YOUR OPINION CAN ONE THING BE IN TWO PLACES AT THE SAME TIME IN THE MACRO WORLD WITHOUT REMOVING THE EXTERNAL REALITY, PHOTONS BEING THE EXEPTION. I KNOW YOU ALREADY ANSWERED THIS IN YOUR PREVIOUS POSTS BUT NOW I FEEL YOUR TELLING ME THAT WITHOUT MATHEMATICAL CERTIANTY ABSOLUTE COLLAPSE CANT BE DETERMINED. CAN THE MATH HOWEVER BE IN SYNCRONICITY WITH THE OBSERVATIONAL RESULTS. I AM SO CONFUSED AND VERY BUYS IN MY LIFE RIGHT NOW THAT I DONT HAVE THE TIME (HOURS OR WHOLE DAY) TO GO THROUGH COMPLEX DOCUMENTS IN QM. PLEASE HELP ME THE BEST YOU CAN ANY OF THE SCI ADVISORS.

SORRY FOR ALL CAPS AND SPELLING IM USING AN ITALIAN COMPUTER THAT DOESENT HAVE SPELL CHECK.

 

[Maui]

In post 13 you asked what happens in the double slit experiment between observations - i.e. you asked for opinions and you received opinions. QM does not describe what happens between observations so you should not protest that you only get opinions. A far better approach would have been to first familiarize yourself with the basic concepts and make up your own mind instead of taking someone's word for it on faith. I was honest with you in not selling you an "explanation" but that somehow got lost on you and the badges.

 

[stevendaryl]

This thread is getting to be too popular. That means it will be closed soon.

(just joking...)

 

[DennisN]

batmanandjoker, may I suggest reading

http://en.wikipedia.org/wiki/Wave_function_collapse

and also please note that there are 17+ [URL="https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/"]interpretations of quantum mechanics[/URL].

And regarding badges, well...
https://www.youtube.com/watch?v=VqomZQMZQCQ

 

[stevendaryl]

and also please note that there are 17+ [URL="https://www.physicsforums.com/insights/fundamental-difference-interpretations-quantum-mechanics/"]interpretations of quantum mechanics[/URL]

And none of them is satisfactory (which I guess is the reason that there are so many--if there were a good one, then everybody would use that one).

 

[atyy]

I really need help here what do you mean by APPARENT collapse can you be specific are you suggesting your not exactly sure that decoherence collapses wave functions IE superposition. Because this is contradicatry to your earlier posts. This is very confusing for me I don't even know where to begin INVESTIGATING whatever diffrence your talking about. Does decoherance cause wave function collapse or create the illusion that it does and everything is still in superposition. Any help would be greatly appreciated.

Apparent means observationaly its the same - but actual collapse is another matter.

The jig is up here - can't give any more detail without the math - it requires knowledge of the difference between proper and improper mixtures which requires considerably more background than you have. Here is the detail for future reference:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Thanks
Bill

I too have had a very hard time too understanding what bhobba means by apparent collapse. In my understanding, from the link he provided, it is the same as collapse. http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf (p38): "Ignorance interpretation: The mixed states we find by taking the partial trace over the environment can be interpreted as a proper mixture. Note that this is essentially a collapse postulate."

 

[stevendaryl]

I too have had a very hard time too understanding what bhobba means by apparent collapse. In my understanding, from the link he provided, it is the same as collapse. http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf (p38): "Ignorance interpretation: The mixed states we find by taking the partial trace over the environment can be interpreted as a proper mixture. Note that this is essentially a collapse postulate."

I think that all that is meant by "apparent collapse" is that one can use mixtures instead of superpositions to compute expectation values. The use of mixtures is consistent with the claim that the wave function has collapsed into some definite state (but it's unknown which one), but it doesn't actually imply it.

 

[atyy]

I think that all that is meant by "apparent collapse" is that one can use mixtures instead of superpositions to compute expectation values. The use of mixtures is consistent with the claim that the wave function has collapsed into some definite state (but it's unknown which one), but it doesn't actually imply it.

I'm not sure I understand correctly, but it seems to me that there are two things that require a proper mixture:
1) filtering measurements, used for state preparation
2) unitary evolution of the mixture after the measurement

The reduced density matrix produces an improper mixture. If one uses the post-measurement mixture for state preparation or evolves it unitarily, then the transition from an improper to a proper mixture is collapse.

 

[audioloop]

Between a sci advisor and some random poster sorry but I prefer to listen to a sci advisor for all I know you might be one of those quantum spiritual types.

good joke !

Beware !

beware of apodictical parrots.


.

 

[audioloop]

Between a sci advisor and some random poster sorry but I prefer to listen to a sci advisor for all I know you might be one of those quantum spiritual types.

Anyways please please in lamen terms if you can distinguish or TRY to explain the diffrence between an observational collapse and an actual or mathematical collapse if that's what your implying. Can one mathematiclly determine collapse while at the same time observe collapse experimentally. Please you would help me a great deal see I suffer from obsessive compulsive disorder and the distortion of reality in my own mind created by my own ignorance of how some suggest the quantum world contradicts the macro classical world creates anxiety for me.

THE BASIC QUESTION IN YOUR OPINION CAN ONE THING BE IN TWO PLACES AT THE SAME TIME IN THE MACRO WORLD WITHOUT REMOVING THE EXTERNAL REALITY, PHOTONS BEING THE EXEPTION. I KNOW YOU ALREADY ANSWERED THIS IN YOUR PREVIOUS POSTS BUT NOW I FEEL YOUR TELLING ME THAT WITHOUT MATHEMATICAL CERTIANTY ABSOLUTE COLLAPSE CANT BE DETERMINED. CAN THE MATH HOWEVER BE IN SYNCRONICITY WITH THE OBSERVATIONAL RESULTS. I AM SO CONFUSED AND VERY BUYS IN MY LIFE RIGHT NOW THAT I DONT HAVE THE TIME (HOURS OR WHOLE DAY) TO GO THROUGH COMPLEX DOCUMENTS IN QM. PLEASE HELP ME THE BEST YOU CAN ANY OF THE SCI ADVISORS.

SORRY FOR ALL CAPS AND SPELLING IM USING AN ITALIAN COMPUTER THAT DOESENT HAVE SPELL CHECK.

what is macroscopic for you ?

objects of
1000 atoms
10000 atoms

100 nm or 1000 nm

macroscopic is beyond 10 ¹⁵ atoms.

the actual experimental limit is 430 atoms.-------
1.-Mass (in grams) equal to the atomic weight (in amu) is called a molar mass.
2.-The collection of atoms in one molar mass is called a mole.
3.-The exact number of atoms in one mole is Avogadro’s number.

Avogadro number
6.022 x 10²³.

 

[stevendaryl]

I'm not sure I understand correctly, but it seems to me that there are two things that require a proper mixture:
1) filtering measurements, used for state preparation
2) unitary evolution of the mixture after the measurement

The reduced density matrix produces an improper mixture. If one uses the post-measurement mixture for state preparation or evolves it unitarily, then the transition from an improper to a proper mixture is collapse.

The miracle of decoherence is that for all practical purposes, there is no difference between using the post-measurement mixture and using a pure state. The only difference is interference terms that are undetectable in practice.

 

[batmanandjoker]

What is the diffrence between pure and mixed states in lamen terms I reasearched it but I am not exactly sure I understood the concept and how it applies to how the enviorment (decoherance) collapses particles.

Also if someone could explain the density matrix and how it applies to all this it would be much appreciated.

 

[atyy]

What is the diffrence between pure and mixed states in lamen terms I reasearched it but I am not exactly sure I understood the concept and how it applies to how the enviorment (decoherance) collapses particles.

Also if someone could explain the density matrix and how it applies to all this it would be much appreciated.

If a system is in a pure state, and you know what the pure state is, then your knowledge of the system is complete, and all uncertainty is quantum. If we take a state to apply to an ensemble, this means that every member of the ensemble has been identically prepared and is in the same state.

A proper mixed state means that you do not know exactly what the quantum state is, but only what the state is with some probability, so uncertainty is due to intrinsic quantum uncertainty, as well as your ignorance of the state. In an ensemble, this means that not all members of the ensemble have been identically prepared.

An improper mixed state comes about when the entire system is in a pure state, but you restrict yourself to observing a subsystem. The improper mixed state describes the behaviour of the subsystem.

The density matrix is a way of writing the quantum state so that pure states, proper and improper mixed states can be described in the same mathematical language.

As I understand, decoherence does not collapse the state. In order to have a definite outcome, one must postulate collapse (or use Bohmian or many-worlds formulations). I believe this is also what is said in bhobba's link to Bas Hensen's essay http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf concerning the "Ignorance interpretation" where one postulates "The mixed states we find by taking the partial trace over the environment can be interpreted as a proper mixture. Note that this is essentially a collapse postulate." (p39). For decoherence to give definite outcomes (see Table 3.1 on p39, where "D. Interactions with the environment explain the apparent definiteness of measurement outcomes." needs all 4 assumptions, including assumption 4 that an improper mixture can be interpreted as a proper mixture.

Decoherence does not explain collapse. Decoherence solves the "preferred basis" or "pointer basis" problem. In particular, decoherence says that position is a usually a very good pointer basis, because interactions are usually local in space. From Hensen's p17: "Summarising, the point is that the basis with respect to which decoherence takes place - i.e. superpositions of eigenstates of this basis decohere into a improper mixture of these eigenstates - is determined by the form of the system/apparatusenvironment interaction Hamiltonian. Therefore the'classical' observables, the ones that we perceive as classical, are exactly those determined by this basis. One of the consequences of this is that any interaction described by a potential V(r), is diagonal in position, and therefore position is always the pointer observable measured by the interaction. many interactions in nature are described by such a potential V (R)." See also sections 2.4 and 3.4 of Bas Hensen's essay.

 

[bhobba]

I think that all that is meant by "apparent collapse" is that one can use mixtures instead of superpositions to compute expectation values. The use of mixtures is consistent with the claim that the wave function has collapsed into some definite state (but it's unknown which one), but it doesn't actually imply it.

Apparent collapse is simple. Technically its that an improper mixed state is observationally indistinguishable from a proper one. If it was a proper one then actual collapse would have occurred.

This has been discussed innumerable times by me and others so I do not know why there is any confusion.

Thanks
Bill

 

[bhobba]

As I understand, decoherence does not collapse the state.

It transforms a superposition to an improper mixed state - see section 1.2.3 of the paper I constantly post about it:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

When one applies the measurement postulate (ie Born's rule) to an improper mixed state you get exactly the same result as if it was a proper one. There is zero, no way, nada, of observationally telling if it was not a proper one instead. If it was a proper one collapse would have actually occurred because a proper one is a specific state randomly presented for observation.

That is what is meant by apparent collapse. That is what is meant by solving the measurement problem FAPP.

The paper I link to gives a fair and balanced view of the issue - but I personally think the language it uses in saying it doesn't touch the central issue is too pessimistic. Its true - but so? If solves it FAPP.

Thanks
Bill