Is partial collapse possible in quantum mechanics? Can you provide an example?

[Varon]

Is it possible for the wave function collapse to be partial because you don't measure everything at once. Can you cite an example?

I read someone mentioned that it's only the superposition relating to the measured quantity that collapses and the superpostion is just expressing the state vector in an eigenbasis for a particular observable in QM, and that the collapse takes place in the view here it's expanded in the eigenstates of the operator. Is it true or mainstream belief?

Also is it true that "collapse may have an internal details that makes it smoother. For example, it takes a certain amount of new evidence to revise a prior expectation. So when you look into details, of position is ACTUALLY "measured" you get into more complicated things... often position is inferred indirectly from other primary observables. Such as momentum etc.". Can you cite any flaw? is this mainstream view?

 

[StevieTNZ]

Is it possible for the wave function collapse to be partial because you don't measure everything at once. Can you cite an example?

Everything being every possible observable? No. One observable - partial information about it state - partial collapse. See my latest post in your thread about particles and QFT.

 

[Varon]

Everything being every possible observable? No. One observable - partial information about it state - partial collapse. See my latest post in your thread about particles and QFT.

What? You said yes in the other thread. I've seen the book pages you mentioned. Anyway. Let's take a simpler example. One electron at a time double slit experiment. Either the electron position becomes known or not. How can there be partial collapse in this one single electron double slit setup?

 

[Varon]

Bohr declared that without measurement to determine its position, the electron has no position.

So in one electron at a time double slit experiment. If the measurement is uncertain, the electron sometimes collapse.. sometimes not... or does it exist in half collapse half wave function state.. are you referring to the former or latter phenomenon in your partial collapse idea?

 

[StevieTNZ]

What? You said yes in the other thread. I've seen the book pages you mentioned. Anyway. Let's take a simpler example. One electron at a time double slit experiment. Either the electron position becomes known or not. How can there be partial collapse in this one single electron double slit setup?

If you think a partial collapse occurs because you haven't measured all observables a quantum system has, then that is incorrect. That was what I was trying to say in my earlier post - apologises if I wasn't clear.

I guess it is about us having probablistic knowledge of a particle going through either slit that is the cause of partial collapse.

These links may be of use to you:

1. http://www.rochester.edu/news/show.php?id=3220
2. http://www.ee.ucr.edu/~korotkov/presentations/10-UCR.pdf

 

[ibysaiyan]

Now I am confused,can someone enlighten us as about partial collapse scenario, whether having not defined a position of a particle leads to a partial collapse?

I was under the impression that the moment we define a particles wavefunction probability,we have chipped in our measurement which leads to an outcome of particle pattern on the screen.

Regards,
ibysaiyan

 

[Varon]

If you think a partial collapse occurs because you haven't measured all observables a quantum system has, then that is incorrect. That was what I was trying to say in my earlier post - apologises if I wasn't clear.

I guess it is about us having probablistic knowledge of a particle going through either slit that is the cause of partial collapse.

These links may be of use to you:

1. http://www.rochester.edu/news/show.php?id=3220
2. http://www.ee.ucr.edu/~korotkov/presentations/10-UCR.pdf

Really? What year do you think is this realized that the quantum system can somehow read our mind and intention? I thought plain measurement is enough to collapse it.

Bohr original proclamation is that in the absence of measurement to determine its position, the electron has no position.

So right now with the updated view. It should be:

In the absence of knowledge of the observer of the position, the particle has no position.

??

 

[Varon]

At the end of one of the website you shared. It is written:

"Because theorists had believed since 1926 that a measurement of a quantum particle inevitably forced a collapse, it was said that in a way, measurements created reality as we understand it. Katz, however, says being able to reverse the collapse "tells us that we really can't assume that measurements create reality because it is possible to erase the effects of a measurement and start again."

What is he saying.. so if measurements don't create reality. It is our knowledge that create reality? But inside a neutron stars.. there are no humans.. how can the neutron star core exist since there is a lack of knowledge inside it? Maybe the particles can have knowledge of one another? But how could particles have knowledge? It's not even alive?

 

[StevieTNZ]

Really? What year do you think is this realized that the quantum system can somehow read our mind and intention? I thought plain measurement is enough to collapse it.

Bohr original proclamation is that in the absence of measurement to determine its position, the electron has no position.

So right now with the updated view. It should be:

In the absence of knowledge of the observer of the position, the particle has no position.

??

I personally don't believe it is the measuring device that causes the collapse of the wave function.

"Because theorists had believed since 1926 that a measurement of a quantum particle inevitably forced a collapse, it was said that in a way, measurements created reality as we understand it. Katz, however, says being able to reverse the collapse "tells us that we really can't assume that measurements create reality because it is possible to erase the effects of a measurement and start again."

I actually think it's not a complete collapse that has been caused in this scenerio. The author makes it seem like a complete collapse did occur, but really only a partial collapse occured. However, it is possible to erase the effects of measurement, e.g. quantum eraser experiments. Again, I have my own views on these experiments and what they mean.


I would say entanglement has something to do with the fact that inside the star is real, because another quantum system exists in a definite state. Entanglement appears even if quantum systems have never interacted. Assuming the universal validity of QM, everything is entangled. If you see a quantum system in a definite state on earth, everything else (because its entangled and would have collapsed upon measurement of either the system on earth, or another system) would be expected to also be in a definite state.

That's my take on these things. Whether I'm correct or not is another debate.

 

[DrChinese]

Is it possible for the wave function collapse to be partial because you don't measure everything at once. Can you cite an example?

Collapse can be partial. For example, you could have entangled photon pairs which are NOT polarization entangled but ARE momentum entangled, wavelength entangled, etc. It is a little hard to see in this reference, but look at (15) and (16). These are entangled bases. This is typical of Type I PDC with a single crystal.

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

Essentially, you know the polarization coming out because a single crystal only passes one input polarization.

Also, it is possible to make weak measurements in which the wave function is only partially collapsed in a specific basis.

Please be cautious with this, as this is some pretty difficult stuff to follow.