Testing double-slit experiment using entangled particles

[truedeity]

I have an idea for an experiment, I will try to explain the setup. Here goes-

 

The experiment is exactly the same as the double-slit experiment, except the only particles which will be sent will be entangled pairs.

 

For each entangled pair, we have a monitoring device which measures its spin continuously, and logs the spin direction to a database along with the time that the spin was measured

 

Near each slit there is some device which influences the magnetic field around the slit in such a way as to change the spin of the particle passing through the slit

 

Since there are two slits, the slit on the right will change any particles passing through it to "spin up", similarly, the slit on the left will change any particles passing through it to "spin down"

 

Lastly, the particles will have to be ordered and indexed to its respective pair in such a way that we can send a stream of particles towards the slit and be able to identify which entangled pair passed through the slit.

 

The idea behind this experiment is to see if it affects the role the observer plays. As the experiment is explained, the observer measures which slit the particle passes through and as a result of that observation the particles wave-like behavior is collapsed.

 

Will logging the entanglement allow us to know which slit the particle goes through without collapsing the wave function?

Edited July 26, 2015 by truedeity

[Klaynos]

The experiment is exactly the same as the double-slit experiment, except the only particles which will be sent will be entangled pairs.

 

For each entangled pair, we have a monitoring device which measures its spin continuously, and logs the spin direction to a database along with the time that the spin was measured

 

I haven't gotten past here yet as assuming you have entangled the spin the first time you measure it you'll break the entanglement.

Your spin fixing at the slits will break the interference pattern (and the entanglement if it hadn't already been broken).

[swansont]

Yep. The entanglement breaks as soon as you measure the spin of either particle.

[truedeity]

Hmm, Since continuous measurement renders the entanglement null. Could the experiment be revised to measuring the particle only once after the particle passes through the slit? Perhaps the wall could have a sensor which triggers the measurement? I'm just not sure if it would be considered unreliable, does spin change too frequently?

 

A particle passing through a slit should be affected by some magnetic field which changes the particles spin. At some point after the particle passes through the slit a measurement can be done on the entangled pair to recover the direction of the spin. Since we have labeled right/left slits for up/down spins respectively we can theoretically know which slit the particle passes through by doing the measurement.

 

So we can have one device for each particle, once the particle hits the back wall (a detector of some sort) a signal can be sent to perform the measurement on that pair. So, we would be sending 1 particle at a time, waiting for the signal, and then measuring spin.

 

Because we are not "observing" which slit the particle passes through the wave function should not be collapsed. If it does collapse, are there any implications?

Edited July 26, 2015 by truedeity

[Klaynos]

You could measure at the wall but I'm not sure what information you'd hope to get from that. As I said you can't influence the spin at the slits add that destroys the interference pattern.

[truedeity]

Why do you think that changing the spin at the slit will destroy the interference pattern?

[swansont]

Why do you think that changing the spin at the slit will destroy the interference pattern?

 

It's not the changing of the spin, it's knowing the spin as you describe the setup — it gives you "which path" information. I'm pretty sure it's possible to do this where you flip the spin (IIRC such transformations are described in teleportation experiments), but what would be the point, if you didn't know the spin to begin with, as must be the case for entanglement?

It's this:

 

Since we have labeled right/left slits for up/down spins respectively we can theoretically know which slit the particle passes through by doing the measurement.

 

Once you know the spins they are not entangled. If you know which slit it went through there is no interference.

[truedeity]

The which path information is only gathered after the fact, after the particle has hit the back wall. I want to clarify my thoughts on that detail. The particle is simply passing through a magnetic field, and in passing we are NOT measuring its spin. Its just that we know the magnetic field around each slit imposes on the spin, of any particle passing through each slit. At that point no measurement is taking place, the particle is passing through a magnetic field, that's it and nothing else. Particles pass through magnetic fields all the time, its just business as usual for particles... since there is no observation on the slit, and the measurement has not been performed, the observer is left out of the experiment and there is no reason the wave function would collapse.

 

I think the way the experiment has been claimed is that as soon as we try to measure which slit the particle passes through, means that the interference pattern goes away (as a result of wave function collapsing due to some observer).

 

Since the particle is entangled, and we have a choice of whether or not we want to measure that entanglement. We can decide any future time to measure the particle spin. For example, 3 hours after the particle hits the wall. If you see a interference pattern on the wall, does that mean that we never get to measure the spin?

[Strange]

Looks like you are describing something like the "quantum eraser" experiment: https://en.wikipedia.org/wiki/Quantum_eraser_experiment

 

This uses entanglement to determine which slit each photon goes through.

 

Note that there is also a delayed version of this, where the observation isn't made until after the interference pattern (or otherwise) is created.

[truedeity]

The particle passes through a magnetic field, in doing its spin is changed.

 

Changing the spin does not mean you have to perform the measurement on the entangled pair. We can wait, and suspend our decision to measure after the results on the experiment are in.

 

The experiment will tell you whether or not you do, even though you have control to measure the entangled pair, or not.

 

Results come in-

A) A interference pattern shows on the back wall. Even though we have control to measure the entangled pair, we do not. The experiment told us what our decision was before we made the choice.

B) The interference pattern is not shown on the back wall (just the two bands). Even though we have the choice not to measure the entangled pair, we "will" and do. The experiment told us what our decision was before we made the choice.

 

What does it say about fate?

The quantum eraser experiment seems similar but different somehow. I actually want to perform the measurements after the results.

 

It seems that in quantum eraser is the measurement is performed after the particle passes through the slit, but BEFORE it his the back wall.

 

My version is a little different- I want to do defer the choice of measurement to after the results come in.

[Klaynos]

If it is possible at some point to find out which slit you will not get an interference pattern. In this case the interaction (magnetic field at the slits) will destroy the pattern. The same interaction breaks the entanglement.

[truedeity]

If it is possible at some point to find out which slit you will not get an interference pattern. In this case the interaction (magnetic field at the slits) will destroy the pattern. The same interaction breaks the entanglement.

As Swansnot said previously its not about changing the spin, its about knowing 'which-path' information. For example, magnetic fields at the slits should not destroy the interference pattern if we are sending non-entangled particles, because it would be impossible to know 'which-path' since there are no entangled particles. So the same should be true for entangled particles as well, because it is based on 'which-path' information. A particles passing through a magnetic field will not have any impact on the experiment since 'which-path' is still unknown. It should be business-as-usual for particles to pass through magnetic fields, its just that magnetic field is changing the spin, if there is no entangled particle it should not impact the experiment, if it is entangled it also should not so long as measurement on the spin is not performed. Because measuring gives you 'which-path' information.

 

 

For the last part of your sentence, I am not sure why you say this "The same interaction breaks the entanglement." How do scientists influence the spin in prior experiments? The reason this seems unlikely to me is because they have to be able to know the particle is entangled to begin with, the only way you can know that is to be able to change the spin, and then perform the measurement of both particles to verify they are entangled. If what your saying is true, how did we ever figure out that particles are entangled to begin with?

[swansont]

The which path information is only gathered after the fact, after the particle has hit the back wall. I want to clarify my thoughts on that detail. The particle is simply passing through a magnetic field, and in passing we are NOT measuring its spin.

 

That's not the scenario you were describing earlier.

As Swansnot said previously its not about changing the spin, its about knowing 'which-path' information.

 

Which is exactly what Klaynos just pointed out. If you have enough information to reconstruct the path, you will not get interference.

 

I'm not sure what your fixation is with the magnetic field. If you do a spin flip on the system, there will be exactly zero effect, regardless of whether the particles are entangled or not.

Changing the spin does not mean you have to perform the measurement on the entangled pair. We can wait, and suspend our decision to measure after the results on the experiment are in.

 

How are you going to detect the particles and then later on measure their spin?

[Strange]

My version is a little different- I want to do defer the choice of measurement to after the results come in.

 

That is, effectively, what the delayed-choice experiment does (if I understand you correctly).

 

What does it say about fate?

 

Nothing. It just says that quantum effects are non-local in time as well as space. It can't be used as an argument for predeterminism.

[truedeity]

 

That's not the scenario you were describing earlier.

 

Which is exactly what Klaynos just pointed out. If you have enough information to reconstruct the path, you will not get interference.

 

I'm not sure what your fixation is with the magnetic field. If you do a spin flip on the system, there will be exactly zero effect, regardless of whether the particles are entangled or not.

 

How are you going to detect the particles and then later on measure their spin?

 

Swansont -

 

Correct, that is not the scenario I described initially, I proposed a new scenario because I did not know that you can only measure the entangled pair once. Initially, I described continuously measuring the entanglement which would not work. I updated my understanding a bit and then revised the experiment. The revision is basically the same as the delayed choice quantum eraser. Except I have a different idea about how to conduct that experiment.

 

I am seeing a bit of miscommunication or misunderstanding about what I am trying to describe, and I think at least 1 potentially false assumption on the opposing side. So in order to discuss this we need to agree about some minor technical details.

 

If I cannot clear up these technical details, a case for predeterminism cannot be made. (Also, I would not call it predeterminism... I would not make a case for predeterminism. I would would presume that the particles are able to travel "forwards" not just backwards in time.)

 

So lets try to work out this issue in our thinking, here is how I view this-

 

1st there is no information to reconstruct the path. There is only information when you measure the entangled pair spin direction. The particle travels forwards in time to when you made the choice to measure the spin, then travels backwards in time to behaving like a particle instead of a wave.

 

If the device measuring the particle is destroyed before measuring the particle, no information is obtained, and 'which-path' cannot be known.

 

So I may be making a case for forward in time travel of quantum particles.

 

To start, someone could devise a basic/simple experiment which uses a magnetic field to change the non-entangled particle spin direction as it enters the slit., and we would only be sending non-entangled particles in order to validate that this alone does not affect the interference pattern. There is no way to know which slit the particle goes through, we just create a device and emit a magnetic field at the slit which we know will affect its spin. In passing particles will not be relaying any information to outside consultants. No body will be calling these particles and asking for a status report, so there is no reason to expect that the double experiment will change its behavior.

[swansont]

You still haven't explained the purpose of flipping the spins.

[truedeity]

I am thinking of two different experiments. The first experiment does not involve entangled particles. The second experiment does.

In the first experiment the purpose of flipping the spin of a non-entangled particle is to demonstrate simply that the spin can change, and that it is an isolated event, and this spin change should not cause the wave function to collapse. There is no way to know which slit the particle passes through, and 'which-path' cannot be known. Since 'which-path' is not known, we should expect to see the interference pattern.

The first experiment is not a quantum eraser, also a difference in the quantum eraser experiment is that prisms are used. I am not using prisms in either the first, or second experiment.

My second experiment is similar to the delayed choice quantum eraser but different because it will involve different equipment and a different way of conducting the experiment.

Second experiment works like this-

Aparatus 1)

Is a "magnetic field generator capable of flipping the spin of a particle to spin up"

Aparatus 1 simply creates a magnetic field which is directed twoards the right slit.

*This aparatus does not measure a particles spin direction. It is just a magnetic field.

Aparatus 2)

Is a "magnetic field generator capable of flipping the spin of a particle to spin down."

Aparatus 2 simply creates a magnetic field which is directed twoards the left slit.

*This aparatus does not measure a particles spin direction. It is just a magnetic field.

Aparatus 3)

Is a device which can measure the spin of an entangled particle.

It has two buttons, red and blue

The red button measures the spin

The bule button causes the device to self distruct, and releases the particle into the atmosphere so it can never be measured.

Aparatus 4)

Responsible for sending particles into the slits.

It is a box with entangled particles inside, attached to the box is a computer which allows the user to type in the serial number of the entangled particle we want to send.

We will need to buy enatngled particles from a lab who can manufacturer them and seperate each entangled particle into aparatus 3, and aparatus 4.

I want to be able to send a specific entangled particle on-demand.

The configuration and setup is exactly the same as the double-slit experiment, except that aparatus 4 is customized to fit our needs of sending specific particles.

The double slit experiment will be tested exactly as it has been in the past where particles are sent one-at-a-time. At the end of an experiment an hour later, we will observe what the results are.

Once the results are in, we will decide whether or not to press the red button, or the blue button, or neither.

Edited July 27, 2015 by truedeity

[Klaynos]

You still haven't explained the purpose of flipping the spins.

I think he's trying to align all the spins through a given slit. So slit a will all be spin up and all through b will be spin down.

 

By adding a "magnetic field to ensure spin up" (or down) you are interacting therefore destroying interference pattern and entanglement.

On measuring the entangled particle in apparatus 3 you destroy the entanglement.

 

 

You will not get an interference pattern out of your experiment as described.

 

I think you are making a common misconception about entangled particles. You entangled a single characteristic (e.g. spin). This entanglement lasts until measurement/observation/an interaction of that characteristic. In the frame of the interaction both wave functions collapse on interaction.

[Strange]

In the first experiment the purpose of flipping the spin of a non-entangled particle is to demonstrate simply that the spin can change, and that it is an isolated event

There is no such thing as an isolated event, in the quantum world especially where entangled particles are concerned.

 

I am not using prisms in either the first, or second experiment.

What is the significance of that?

 

 

Is a device which can measure the spin of an entangled particle.

 

How does it do that?

 

It is a box with entangled particles inside, attached to the box is a computer which allows the user to type in the serial number of the entangled particle we want to send.

 

I don't think it is possible to have a box of entangled particles. Their interactions will destroy any entanglement. (You certainly can't buy such from a supplier.)

 

All particles (of a given type) are identical so I have no idea how you are going to put serial numbers on them.

 

Also, what is the significance of being able to select a particular particle pair?

 

And it is not clear what you are doing with the pair? Are you sending them both through the slits? Or just one?

[truedeity]

 

 

By adding a "magnetic field to ensure spin up" (or down) you are interacting therefore destroying interference pattern and entanglement.

 

 

I understand why interacting will destroy the entanglement. But I am thinking that this interaction will not destroy the interference pattern. The double-slit experiment has never been invoked in this manner. Partly, this is why I came up with Experiment #1. What is it about your knowledge that makes you think this type of interaction will collapse the wave function? Can you elaborate on that? If what your saying is true, adding a magnetic field around either of the slits will always result in a double band. Has that ever been tested?

 

 

 

On measuring the entangled particle in apparatus 3 you destroy the entanglement.

 

 

Because I only need to measure the particle once, after the results are in, I don't care if I destroy the entanglement.

Strange-

 

The significance is just that my version is different. There may be fundamental similarities but a totally different setup.

 

 

 

I don't think it is possible to have a box of entangled particles. Their interactions will destroy any entanglement. (You certainly can't buy such from a supplier.)

 

This is a technical impediment not necessarily an impossibility. A lot will have to be designed and worked out to configure Apparatus 4. Something like a CD changer, once you select which pair you want to send a carton containing the particle is loaded and ready to be fired.

 

 

 

All particles (of a given type) are identical so I have no idea how you are going to put serial numbers on them.

 

I won't be putting serial numbers on the particles themselves. The serial numbers will correspond to a particular entangled pair, or one of the Apparatus 3 boxes. Each box contains one of the pair particles. The serial number will be written on the box.

 

 

The image below taken from Wikipedia shows how the particles accumulate when being sent one-at-a-time, the result is single particles appearing on the screen. This is the version of the experiment Apparatus 4 performs.

 

https://en.wikipedia.org/wiki/Double-slit_experiment#/media/File:Double-slit_experiment_results_Tanamura_2.jpg

Edited July 27, 2015 by truedeity

[Klaynos]

A simple answer is that to interact on that way you must confine the particle to either slit a or b. The double slit experiment requires particles to travel through both slits simultaneously. Your interaction collapses the wave function.

[Strange]

I understand why interacting will destroy the entanglement. But I am thinking that this interaction will not destroy the interference pattern.

 

Maybe you need to study quantum theory so you can actually calculate what the results of the experiment will be (as was done for all the other variations).

 

 

I won't be putting serial numbers on the particles themselves. The serial numbers will correspond to a particular entangled pair, or one of the Apparatus 3 boxes. Each box contains one of the pair particles. The serial number will be written on the box.

 

You miss the point: all the particles are identical. What is the point of being able to select a particular pair of particles?

 

Why do you want to store entangled pairs in boxes? Why not just generate them as you need them?

[swansont]

 

It is a box with entangled particles inside, attached to the box is a computer which allows the user to type in the serial number of the entangled particle we want to send.

 

"Serial number" does not play nicely with the notion that these particles are indistinguishable.

[Strange]

It is a bit like hoping to win the lottery when the machine is filled with 47 identical matt black balls.

[truedeity]

I did not explain why I added the serial numbers, that's why you guys don't understand it completely. It's really a waste of energy to spend time on it though, I will not need it since the experiment is null. Serial numbers are for tracking, and I wanted to do tracking. The reason it is this way is because as particles are being sent one-at-a-time, we know which particle we are sending and when we are sending it. So when it lands on the back wall, I could point to that specific particle and say, "this particle was the 4th particle we sent, this particles pair is in this box."