B Can a Quantum Observer Perceive Superpositions Inaccessible to Humans?

[Nugatory]

I'd like to ask this simple question. Supposed you were walking in the street and there was no simple outcome.. meaning no particular position eigenstates selected.. does it mean the entire neighborhood and street would moving back and forth without any particle positions in all the particles although position preferred basis selected or would you see nothing?

That question has no satisfactory answer because for you to see something implies that light is interacting with your eyes. Either one set of rod and cone cells in your retina is triggered to form one image, or a different set is triggered to form another image; either way we see a definite outcome and not a superposition. Similar arguments apply to other senses (your eardrum ends up in a definite state after interacting with the air molecules that carry sound, for example) but this argument in no way privileges human sensory apparatus. A piece of photographic film will also capture one image or the other, and the process is not interestingly different from the process by which your retina captures one image or the other.

Do not be misled by our ability to see and photograph an interference pattern in the double-slit experiment. Each individual particle makes its own unsuperimposed position-basis dot on the screen so we aren't seeing any superposition. We're seeing the statistical result of a large number of experiments (one per dot) in which we've allowed a superposition to collapse before we observe it.

I just want to imagine how it would behave. Remember I'm writing a book on cartoon guide to decoherence for the masses. So need impressive example.

My advice is to get hold of Bruce Lindley's book "Where does the weirdness go?", read through it, and then try recasting it as a cartoon guide.

 

[cube137]

If you are walking down the street then everything is decohered into the position basis. For the why you have to consult technical tomes - but it has to do with most interactions having radial symmetry.

As for the measurement problem it most assuredly does not solve that - but that is way off the query you asked. It requires a thread of its own.

You seem to be caught up with what it would be like to be a pure state thinking it would become unreal or something like that. What me and others have been trying to get across is pure states are rather difficult to come by even for things like electrons, but utterly impossible for macro objects like cats.

Thanks
Bill

Can you give some examples of pure states. Can the electron passing thru both slits and interfering count as one (before the detector cause decoherence or collapse)? Here the electron can interfere with it. So it's not entirely wrong to call or think it would "become unreal or something like that" as you put it. How can pure state be real when a particle can interfere with itself. So after emission and before detector. We can say the electron become unreal indeed.

 

[bhobba]

Can you give some examples of pure states.

The truth is what Professor Neumaier said in another thread:
There is no way to remove the decoherence for a macroscopic object. You can do it (approximately) only for very tiny objects such as electrons or buckyballs - and the cost for doing it grows drastically with the size of the object.

You have seen a number of cases in this thread where states are modeled as pure, as well as the elections and buckyballs mentioned above where it is often a good approximation.

Can the electron passing thru both slits and interfering count as one (before the detector cause decoherence or collapse)?

In this case electrons are treated as pure to good approximation as is rather clear from the literature.

While it is common in the literature to say electrons pass through both slits in fact QM is silent on what's happening when objects are not observed. That's the territory of interpretations - in this case Feynman's sum over histories. Here is much better way of looking at the double slit:
http://arxiv.org/ftp/quant-ph/papers/0703/0703126.pdf

How can pure state be real when a particle can interfere with itself. So after emission and before detector. We can say the electron become unreal indeed.

We deal with science here not new age philosophical mumbo jumbo such as things becoming unreal. Philosophers can't even agree on what real is. In science we take a very common sense view of reality and think of science as describing it. Personally I believe reality is what science describes - but that's just me, and here, by forum rules, is not the place to discuss philosophy. When not observed QM is silent on what's going on. But interpretations have all sorts of takes from very real such as BM to I basically give up like Ignorance Ensemble.

Thanks
Bill

 

[cube137]

You have seen a number of cases in this thread where states are modeled as pure, as well as the elections and buckyballs mentioned above where it is often a good approximation.
In this case electrons are treated as pure to good approximation as is rather clear from the literature.

Thanks
Bill

Bill. I've been doing some researching. According to physicist JesseM, it may be possible to prepare pure state for the cat.. he said in an old thread:

"In principle it should be possible to prepare the contents of the box in a pure state, which I think just means you would perform a measurement that would give you the maximum possible information about the particles in the box allowed by quantum physics (like a precise measurement of a complete set of commuting observables), allowing you to construct a state vector for the system."

Bill.. In pure state, you have interferences in the phases.. if a cat would be prepare in pure state.. there may still be a very tiny portion of all the zillions and zillions of particles where there may be interferences.

I think he meant that as long as there is a tiny interference (non-zero).. it can be called pure state? perhaps in your view, pure state should be complete interferences? Is your view or his the mainstream belief? How do you interpret his statements?

 

[bhobba]

Bill. I've been doing some researching. According to physicist JesseM, it may be possible to prepare pure state for the cat.. he said in an old thread:

He is wrong - if he is saying that - which is doubtful. I have explained why - its basic QM that you can't.

which I think just means you would perform a measurement that would give you the maximum possible information about the particles in the box allowed by quantum physics (like a precise measurement of a complete set of commuting observables), allowing you to construct a state vector for the system."

That is not what a pure state is. Its independent of the measurement you can perform on it. You are likely not giving the proper context which is what's known as a state preparation procedure. You can't do that with a cat since it breaths air, but state preparation procedures are outside this tread and needs one of its own.

Instead of twisting this way and that trying to justify an incorrect notion you came to this forum with, learn the theory from the sources that have been mentioned in this thread. That way you will be in a better position to see when even physicists get things wrong if he got it wrong - which I doubt.

For completeness I will tell you exactly what a pure state is. A state in QM is by definition a positive operator of unit trace. States of the form |a><a| are called pure. States of the form Σ pi |ai><ai| are called mixed. Its easy to show any state must be mixed or pure. For pure states the |a> in |a><a| can be mapped to a vector space which is how they are usually presented in beginner and intermediate texts - but more advanced texts tell the whole story. Its an example of something you have to unlearn as you progress which unfortunately happens on occasion in physics and sometimes leads to confusion. This is a famous example, the idea of virtual particles as particles is another. They lead to thread after thread here because people for some reason don't want to unlearn what they have been told elsewhere. Its a very frustrating human quirk.

Once you understand the above you can see what that guy wrote is off target but more likely you are taking it out of context.

Why are states positive operators of unit trace? There is a very beautiful theorem called Gleason's theorem:
https://en.wikipedia.org/wiki/Gleason's_theorem

Why can't a cat be in a pure state. He breaths air and is entangled with the air because the cat interacts with the air. The link I gave previously explains what that implies ie its no longer is a separate state, but acts like a mixed state.

Thanks
Bill

 

[Evo]

Closed pending moderation.

Edit: this thread is going in circles and will remain closed