Macro Superposition: Does Size Matter?

[batmanandjoker]

My question preferibily if sci advisors could answer this as objects get bigger does the radius or space of its superposition become smaller to the point at which it is so miniscule its hard to notice. Wheras smaller objects like atoms have huge superpositions and can be in california and new york at the same time. On the other hand the superposition of a pencil is so small that its the microscopic size of a Angstrom.

Any help is appreciated

 

[audioloop]

you can manipulate to be precise,
more spread momentum, less spread position.

 

[batmanandjoker]

I don't understand can you clarify please and adress whether there is a diffrence in superposition size between macro and micro objects.

 

[bhobba]

The wavelength of the 'wave-packet' of large objects is so small its virtually impossible to detect its quantum character.

Thanks
Bill

 

[batmanandjoker]

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.

 

[ZapperZ]

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.

Look at what they needed to do to "detect" it.

Size isn't the issue. It's the ability to maintain coherence over space and time! It gets progressively more difficult to maintain such coherence as the object gets bigger, and thus, makes it more difficult to detect such quantum effects.

Zz.

 

[bhobba]

It's the ability to maintain coherence over space and time!

That's exactly it. Left to itself a wave-packet will naturally spread. What keeps it from doing that is its decohered by the environment.

In the linked article they spent a lot of effort removing the environment. That's very hard to do, but not impossible. But when its done some very strange effects appear even for macro objects.

Nowadays we know fairly well the reason we have a classical world is its constantly being entangled with its environment and decohered. For example a few stray photons from the CBMR is enough to decohere a dust particle and give it a definite position.

Thanks
Bill

 

[batmanandjoker]

Then why does the double slit experiment with a laser pen forexample display an interferance pattern in high school class experiments since in the classroom the enviorment has not obviously been removed yet we can see superposition on the backboard.

 

[ZapperZ]

Then why does the double slit experiment with a laser pen forexample display an interferance pattern in high school class experiments since in the classroom the enviorment has not obviously been removed yet we can see superposition on the backboard.

It is because photons do not interact that much with the air environment. That's why we use photons in many EPR-type experiment - they maintain coherence longer in time and distance!

Zz.

 

[batmanandjoker]

Does this only apply to photons

 

[ZapperZ]

Does this only apply to photons

Does what apply only to photons?

Zz.

 

[PhysicsStuff]

I think he means "does interference only apply to photons" in which case I think the answer is no, you can observe decoherence and constructive and destructive interference with just about any lepton.

 

[batmanandjoker]

My real question is it only photons that we can see macro superposition IE double slit interferance without isolating the particles from the outside world.Are photons "special" in this regard.

 

[Maui]

My real question is it only photons that we can see macro superposition IE double slit interferance without isolating the particles from the outside world.Are photons "special" in this regard.

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.

 

[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-makeover


BTW, if you want a real understanding of what is going on, a 'bare' decoherence theory will only get you half-way at most.

is this true in refrence to electrons, I feel there is a contradiction between entanglment forming a classical world and the double slit exhibiting superpositions of diffrent particles

 

[Maui]

is this true in refrence to electrons

What do you mean? The link I posted was about an experiment done with electrons.

All quantum particles can show interference effects, it's just that the bigger the object, the harder it is for quantumness to be observed(massive accelerated particles display almost classical behavior). What is it that you are asking?

 

[batmanandjoker]

What I am asking is the double slit experiment the only example of superposition in the macro world without isolating the particles from the external enviorment and are there other examples other than the double slit. The sci advisors in the above posts said that when a particle interacts with the outside world it loses its quantum properties "entanglment occurs" and collapses yet the double slit contradicts this. I am very confused at this point also the link I posted earlier about the metal paddle its superposition or eigenstates must be very small or miniscule correct.

Any answers from mentors or sci advisors would be greatly aprreciated.

 

[Maui]

What I am asking is the double slit experiment the only example of superposition in the macro world without isolating the particles from the external enviorment and are there other examples other than the double slit. The sci advisors in the above posts said that when a particle interacts with the the outside world it loses is quantum properties and collapses yet the double slit contradicts this.

No. Bigger objects do tend to lose their coherence very fast and there have been experiments with double slits and more massive objects where special measures were taken to avoid decoherence. With single free electrons decoherence plays much lesser role.

I am very confused at this point also the link I posted earlier about the metal paddle its superposition or eigenstates must be very small or miniscule correct.

Any answer from mentors or sci advisors would be greatly aprreciated.

That paddle is almost a classical object and in no way comparable to single electrons or photons. It's huge and massive.

 

[batmanandjoker]

But can someone other than maui explain how we live in an entangled world which is always collapsed by the enviorment but at the the same time the double slit expeirment can be performed with particles IE electrons not isolated by the enviorment and not collapse. There is an inconsistinsy here.

 

[bhobba]

But can someone other than maui explain how we live in an entangled world which is always collapsed by the enviorment but at the the same time the double slit expeirment can be performed with particles

There is no inconsistency.

Entanglement, and decoherence is a form of entanglement, requires interaction. If things are arranged so the interaction is weak, and hence negligible, then interference effects can occur.

Crystal diffraction, which demonstrates the quantum nature of electrons, I believe is done in a vacuum. Not likely to be much interaction there.

IE electrons not isolated by the enviorment and not collapse.

Like I said I am pretty sure its done in a vacuum. Valves for example need a reasonably good one to have an electron stream to even work.

Thanks
Bill

 

[batmanandjoker]

so cooling a tiny metal paddle until it reached its quantum mechanical 'ground state' — the lowest-energy state permitted by quantum mechanics untangles the paddle from the external enviorment. Why and how does cooling or tempature manipulation separate macro objects from the external enviorment IE decoherence. And at what point is a micro object considered a macro object what's the tipping point.

 

[ZapperZ]

But can someone other than maui explain how we live in an entangled world which is always collapsed by the enviorment but at the the same time the double slit expeirment can be performed with particles IE electrons not isolated by the enviorment and not collapse. There is an inconsistinsy here.

You really should look up the circumstances surrounding these experiments here. There are plenty of stuff you can find on the web!

The electron double slit experiment, and in fact, ALL electron diffraction experiments, are done in vacuum! I perform electron diffraction experiments almost every week (LEED and RHEED), and they are all in 10^-9 Torr or better! These electrons don't interact with the "environment". If they do, you'll loose the single-particle coherence.

Also, please read this:

https://www.physicsforums.com/showpost.php?p=1498616&postcount=55

There are NO inconsistencies here.

Zz.

 

[batmanandjoker]

so cooling an object to extreme tempatures creates a vacuum is this correct also if something as big as a truck is put in a vacuum I know it will exhibit superposition but will it be a smaller superposition than say the paddle in a vaccum.

 

[ZapperZ]

so cooling an object to extreme tempatures creates a vacuum is this correct also if something as big as a truck is put in a vacuum I know it will exhibit superposition but will it be a smaller superposition than say the paddle in a vaccum.

You are all over the place here.

Cooling an object has nothing to do with creating a vacuum. I dip something in liquid nitrogen. Did I just create a vacuum? Think about it.

Zz.

 

[audioloop]

so cooling an object to extreme tempatures creates a vacuum is this correct also if something as big as a truck is put in a vacuum I know it will exhibit superposition but will it be a smaller superposition than say the paddle in a vaccum.

there are planned experiments on bigger objects in decoherence free ambients to see if the superposition persist or is lost.


.

 

[bhobba]

so cooling a tiny metal paddle until it reached its quantum mechanical 'ground state' — the lowest-energy state permitted by quantum mechanics untangles the paddle from the external enviorment. Why and how does cooling or tempature manipulation separate macro objects from the external enviorment IE decoherence. And at what point is a micro object considered a macro object what's the tipping point.

Its obvious. Take temperature. For an object to heat up it needs to come into contact with objects at a higher temperature or absorb radiation (ie photons) or something similar. It gets entangled with it. This is basic thermodynamics.

One of the issues here is physics is a highly interconnected area. If you want to delve into advanced areas such as exactly how we get things to show quantum behavior, rather than like most people at the beginning level simply accept things have been so arranged for it to happen, then stuff that is rather obvious once you have gone a bit beyond that, but is opaque until you do, make it difficult to sort things out.

The temperature quantum effects start to show themselves depends on the object, but generally its a technological tour-de-force accomplishing it.

The simplest is probably liquid helium:
http://en.wikipedia.org/wiki/Liquid_helium

Thanks
Bill

 

[bhobba]

so cooling an object to extreme tempatures creates a vacuum is this correct also if something as big as a truck is put in a vacuum I know it will exhibit superposition but will it be a smaller superposition than say the paddle in a vaccum.

Like Zapper said you are all over the place.

You need to remove interactions to prevent decoherence. There are many causes of interaction - excitation from somewhere that raises temperature (eg being jostled by molecules and atoms you are in contact with or radiation ie photons), air, etc etc.

Its absolutely insidious as far as maintaining coherence is concerned - as I often post a few stray photons from the cosmic background radiation is enough to decohere a dust particle and give it a position. Eliminating all this is not trivial.

It is a technological nightmare to show quantum effects for macro objects (other than stuff like say holes in semiconductors that are required for transistors to work - but I don't think that's what you have in mind). Its a marvel it has been done - but when done some very strange effects emerge.

Doing it for photons is easy - they interact even weakly with air. Electrons is harder - you need a vacuum - but doing that has been around for quite a while eg thermionic valves. Macro objects is however a whole new ball game we are only now starting to really get into. We have had stuff like liquid helium around, but that is only the start.

Thanks
Bill

 

[Maui]

So electrons shot by an electron gun should decohere upon passing through the slits(due to interaction) and only display classically permited behavior. But they don't.

 

[batmanandjoker]

because they are shot in a vaccum. Any ways I am all over the place because I am quite confused being a beginner but I have another question superposition is just a statistical probability wave function. Is this correct and if someone could adress some of my earlier and I know stupidly obvius questions for sci advisors it would be much appreciated. I appreciate all the help you all have given me so far.

 

[Maui]

because they are shot in a vaccum.

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.

 

[bhobba]

but I have another question superposition is just a statistical probability wave function. Is this correct and if someone could adress 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.