Preparing Quantum Systems: Understanding State Preparation and Its Importance

[bhobba]

But Maui emphasized to Bill "Experiments prove that the world is quantum and not classical. You should not pretend you are explaining the quantum to classical transition by stating the obvious

That's his view. My view is he needs to think more carefully about what explanation is. Every explanation has primitives. You can explain them in terms of others but then you have to explain those primitives - and so it goes. What he is doing is saying he doesn't like my assumption of an improper mixture - somehow (there are a number of other interpretations that explain it - but of course they have their own assumptions you may like or dislike) becomes a proper one - its like Newton said regarding gravity - I make no hypothesis. Under Maui's view Newton should not have pretended he understood gravity - nor should Einstein pretend he understood gravity after basing it on no prior geometry (that's the modern view of what Einstein did). Everyone that has studied the theory recognises that GR is a much better and more elegant theory - no prior geometry is very intuitively appealing. But does it explain gravity - why does nature have no prior geometry - you should not pretend you understand gravity until you can explain that.

Lucas this is really a philosophical issue on what explain means. This is a forum that discusses physics - not philosophy. Maybe your time can be better spent delving into the detail of the theory rather than foundational issues - especially foundational issues more concerned with general science foundations.

Why is this not popular. In Tegmark's we are living in simulations inside a program. Improper mixture becomes proper simply because it is what the program do... that is.. rather than saying the quantum state is real and having to face paradox of Wigner friend.

Maybe because its basically philosophical semantic BS not expressed in the language of physics - math. If such an idea can be given a mathematical basis then it may garner some support. It's like saying maybe QM is explained by impinging multiple realities - why isn't that taken seriously. It's vacuous until it expressed in mathematics:
https://app.griffith.edu.au/news/2014/10/27/new-quantum-theory-is-out-of-this-parallel-world/

Once it is it can be checked to see if it holds up.

Thanks
Bill

 

[lucas_]

That's his view. My view is he needs to think more carefully about what explanation is. Every explanation has primitives. You can explain them in terms of others but then you have to explain those primitives - and so it goes. What he is doing is saying he doesn't like my assumption of an improper mixture - somehow (there are a number of other interpretations that explain it - but of course they have their own assumptions you may like or dislike) becomes a proper one - its like Newton said regarding gravity - I make no hypothesis. Under Maui's view Newton should not have pretended he understood gravity - nor should Einstein pretend he understood gravity after basing it on no prior geometry (that's the modern view of what Einstein did). Everyone that has studied the theory recognises that GR is a much better and more elegant theory - no prior geometry is very intuitively appealing. But does it explain gravity - why does nature have no prior geometry - you should not pretend you understand gravity until you can explain that.

Lucas this is really a philosophical issue on what explain means. This is a forum that discusses physics - not philosophy. Maybe your time can be better spent delving into the detail of the theory rather than foundational issues - especially foundational issues more concerned with general science foundations.
Maybe because its basically philosophical semantic BS not expressed in the language of physics - math. If such an idea can be given a mathematical basis then it may garner some support. It's like saying maybe QM is explained by impinging multiple realities - why isn't that taken seriously. It's vacuous until it expressed in mathematics:
https://app.griffith.edu.au/news/2014/10/27/new-quantum-theory-is-out-of-this-parallel-world/

Once it is it can be checked to see if it holds up.

Thanks
Bill

Thats right. better delving into details of theory. In one of papers you shared.. the one by Bas Hensen. Its stated " System 2 is said to be a proper mixture, versus system 3 which is in a improper mixture. When a measurement is performed on the discarded part B of system 3, but we are not told of the outcome (ignorance), system 3 reduces to a proper mixture, and systems 2 and 3 are then physically identical.". So you are saying that if we can do measurements on the entire system and environment (not possible but let's say we can theoreticaly).Then its proper mixed state and there before observation and no collapse needed? So you called it improper because you can't measure the entire system and environment? But if you can, its proper mixture and the measurement problem solved and there is outcome? Or is th problem why there is outcome still not solved even if you can measure the entire system and environment making it proper mixture?

 

[bhobba]

So you called it improper because you can't measure the entire system and environment?

I called it improper because of the definition I gave previously. Section 1.2.3 of that paper says exactly what I have been saying. Equation 1.22, for system 2, and equation 1.23 for system 3 are exactly the same - but prepared differently. 1.22 is a proper mixed state - 1.23 is an improper mixed state.

''System 2 is in a definite deterministic physical state, whereas system 3 is part of a composite superposition state. Its physical state is truly undetermined, as long as no measurement is performed on “part B” of system 3 (that we removed from our control). System 2 is said to be a proper mixture, versus system 3 which is in a improper mixture. When a measurement is performed on the discarded part B of system 3, but we are not told of the outcome (ignorance), system 3 reduces to a proper mixture, and systems 2 and 3 are then physically identical. In the previous section we (Gleason[5]) proved that the density operator is the most general description of measurement statistics of a quantum system, and yet we just stated that although ρ2 = ρ3, they are physically not the same state. How can this be so? The answer is that indeed we are unable to discern systems 2,3 by any local measurement, since at the level of the systems 2,3 the density operator is indeed the most fundamental object describing the measurement outcome probabilities, but looking at the global state including the discarded part B of system 3, we find that systems 2,3 are different. This difference between proper and improper mixtures will play an important role when we come discuss the implications of environment-induced decoherence on the quantum to classical transition in chapter 3.'

I seem to be going over and over the same stuff with you. I believe its because you have not yet come to grips with the math due to a fascination with philosophical semantics rather than the underlying math. That is not what physics is about. I will not be replying any more to queries along those lines.

Please take the time to come to grips with the math.

Thanks
Bill

 

[lucas_]

I called it improper because of the definition I gave previously. Section 1.2.3 of that paper says exactly what I have been saying. Equation 1.22, for system 2, and equation 1.23 for system 3 are exactly the same - but prepared differently. 1.22 is a proper mixed state - 1.23 is an improper mixed state.

''System 2 is in a definite deterministic physical state, whereas system 3 is part of a composite superposition state. Its physical state is truly undetermined, as long as no measurement is performed on “part B” of system 3 (that we removed from our control). System 2 is said to be a proper mixture, versus system 3 which is in a improper mixture. When a measurement is performed on the discarded part B of system 3, but we are not told of the outcome (ignorance), system 3 reduces to a proper mixture, and systems 2 and 3 are then physically identical. In the previous section we (Gleason[5]) proved that the density operator is the most general description of measurement statistics of a quantum system, and yet we just stated that although ρ2 = ρ3, they are physically not the same state. How can this be so? The answer is that indeed we are unable to discern systems 2,3 by any local measurement, since at the level of the systems 2,3 the density operator is indeed the most fundamental object describing the measurement outcome probabilities, but looking at the global state including the discarded part B of system 3, we find that systems 2,3 are different. This difference between proper and improper mixtures will play an important role when we come discuss the implications of environment-induced decoherence on the quantum to classical transition in chapter 3.'

I seem to be going over and over the same stuff with you. I believe its because you have not yet come to grips with the math due to a fascination with philosophical semantics rather than the underlying math. That is not what physics is about. I will not be replying any more to queries along those lines.

Please take the time to come to grips with the math.

Thanks
Bill

I know the math and I read that paragraph a dozen times in the paper. I was just verifying or confirming coming from you whether you called it improper because you can't measure the entire system and environment and if you can it's proper mixture and measurement problem solved, just say "yes", that will do.

But then I read atyy saying the following "If one measures observables confined to the subsystem, then no experiment can distinguish proper and improper mixed states. However, if one can measure the system and the environment then proper and improper mixed states can be distinguished. http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf (see section 1.2.3 on p10)

Regardless of what one measures, decoherence does not solve the measurement problem because the system as a whole is still in a superposition of measurement outcomes. It does not make sense to say there is an outcome on the subsytem, but no outcome on the environment.".

In my last message. I was confirming if you agreed with atyy too. This is the part confusing so hope others can help shed the light and conclude it. It seems that in bhobba view. If he can measure the entire system-environment, then it's mixed state and problem solved. But atyy didn't seem to agree and state that even if Bill can measure the entire system-environment, it doesn't solve the measurement problem "because the system as a whole is still in a superposition of measurement outcomes".

 

[bhobba]

if one can measure the system and the environment then proper and improper mixed states can be distinguished.

Precisely what don't you understand about local that I highlighted?

Anyway its my last comment on it.

Thanks
Bill

 

[lucas_]

Precisely what don't you understand about local that I highlighted?

Anyway its my last comment on it.

Thanks
Bill

Of course I understood it. That was why I mentioned what if you could measure the *entire* system and environment.. meaning it's not local... then it all becomes proper. This is connected to this thread why one need to prepare the state by doing multiple measurement.. in the improper thing.. it's related to the knowledge of the instrumentalist.. if he could measure all the environment.. then it's improper and there is measurement problem.. it's as if his knowledge alone can change things.. because if it's proper... measurement problem solved.. but atyy didn't seem to agree.. anyway.. just one advice for you.. for 4 years you kept using the same sentence structure about apparent collapse.. hence if one misunderstood before, he can again and again.. next time.. just use other way of expressing them. For others who may know if Bill's stuff differ to atyy. Please share a few words before this thread is dead. Thank you.

 

[bhobba]

Please share a few words before this thread is dead.

You are saying if its not local then it may not be true - but it specifically says its local so what your issue is has me beat.

That's it - no more comments.

Thanks
Bill

 

[lucas_]

You are saying if its not local then it may not be true - but it specifically says its local so what your issue is has me beat.

That's it - no more comments.

Thanks
Bill

Someone else who understood improper vs proper. Pls. confirm the following is how Bill misunderstood. In the passage he kept quoting "''System 2 is in a definite deterministic physical state, whereas system 3 is part of a composite superposition state. Its physical state is truly undetermined, as long as no measurement is performed on “part B” of system 3 (that we removed from our control). System 2 is said to be a proper mixture, versus system 3 which is in a improper mixture.".

But then "system 3 is part of a composite superposition state" is just like system + environment in decoherence, the environment being the "discarded part B of system 3". This is the reason I asked him the simple question "So you called it improper because you can't measure the entire system and environment?". In the context above. My question is accurate. Because in measurements, we can measure the entire system. what is the problem is the environment that we don't have control to. Unless he is saying the improper mixed state is only related to the system and not the environment.. but when performing the trace.. we trace our the environment giving the reduced density matrix.. therefore the environment is the "part B of system 3 (that we removed from our control). Please anyone confirm this as I've been thinking of this the whole day. Thanks a lot.

 

[lucas_]

I called it improper because of the definition I gave previously. Section 1.2.3 of that paper says exactly what I have been saying. Equation 1.22, for system 2, and equation 1.23 for system 3 are exactly the same - but prepared differently. 1.22 is a proper mixed state - 1.23 is an improper mixed state.

''System 2 is in a definite deterministic physical state, whereas system 3 is part of a composite superposition state. Its physical state is truly undetermined, as long as no measurement is performed on “part B” of system 3 (that we removed from our control). System 2 is said to be a proper mixture, versus system 3 which is in a improper mixture. When a measurement is performed on the discarded part B of system 3, but we are not told of the outcome (ignorance), system 3 reduces to a proper mixture, and systems 2 and 3 are then physically identical. In the previous section we (Gleason[5]) proved that the density operator is the most general description of measurement statistics of a quantum system, and yet we just stated that although ρ2 = ρ3, they are physically not the same state. How can this be so? The answer is that indeed we are unable to discern systems 2,3 by any local measurement, since at the level of the systems 2,3 the density operator is indeed the most fundamental object describing the measurement outcome probabilities, but looking at the global state including the discarded part B of system 3, we find that systems 2,3 are different. This difference between proper and improper mixtures will play an important role when we come discuss the implications of environment-induced decoherence on the quantum to classical transition in chapter 3.'

I seem to be going over and over the same stuff with you. I believe its because you have not yet come to grips with the math due to a fascination with philosophical semantics rather than the underlying math. That is not what physics is about. I will not be replying any more to queries along those lines.

Please take the time to come to grips with the math.

Thanks
Bill

I studied Maximillian reference and math. And there it is clear I am right and Bill is wrong (admit it). In page 45:

"Before deriving (2.41), let us first discuss the importance of the concept of reduced density matrices for the description of decoherence. Recall that decoherence arises from interactions between two systems, namely, the "system of interest" and its environment. Typically, such interactions will then lead to an entangled state for the system-environment combination. Usually, the observer will perform measurements only on the system of interest, whereas the environment is typically either inaccessible, cannot be completely measure, or is simply of no interest." so my question is accurate. I ask Bill "if one can measure the system and the environment then proper and improper mixed states can be distinguished". His answer should be a clear yes. Instead he has to use the example of Hensen where the example speaks of system A and system B. In my question, I was referring to Maximillian context where the system B is the environment. So if truth is important to you, admit this Bill you got it misunderstood instead of telling me I misunderstood (which if I do, I stand corrected.. but I'm right this time).