Testing the Schrödinger cat

[viole]

This is a question for the physicists here. I am not, so I don't know the answer, even though I have a strong suspicion.
I would like to propose a more animal friendly variant of the Schrödinger cat thought experiment.

Suppose that the cat is a conscious experimenter that performs a measurement of the spin of an electron in a certain direction. Previous to measurement, the spin is in a perfect superposition of the two eigenstates up and down.

The box in which the cat is hidden has two tiny slits. If the cat observes up, it sends a photon through the left slit. If it measures down, it sends a photon through the right slit. There is no other way for external observers to know what the cat measured.

The photon then travels out of the box toward a screen in the lab. No external measurement is performed that could determine from which slit the photon comes.

Do I observe interference on the screen?

Ciao

- viole

 

[12jtartar]

This is a question for the physicists here. I am not, so I don't know the answer, even though I have a strong suspicion.
I would like to propose a more animal friendly variant of the Schrödinger cat thought experiment.

Suppose that the cat is a conscious experimenter that performs a measurement of the spin of an electron in a certain direction. Previous to measurement, the spin is in a perfect superposition of the two eigenstates up and down.

The box in which the cat is hidden has two tiny slits. If the cat observes up, it sends a photon through the left slit. If it measures down, it sends a photon through the right slit. There is no other way for external observers to know what the cat measured.

The photon then travels out of the box toward a screen in the lab. No external measurement is performed that could determine from which slit the photon comes.

Do I observe interference on the screen?

Ciao

- viole

Maybe!!!

 

[sayak83]

This is a question for the physicists here. I am not, so I don't know the answer, even though I have a strong suspicion.
I would like to propose a more animal friendly variant of the Schrödinger cat thought experiment.

Suppose that the cat is a conscious experimenter that performs a measurement of the spin of an electron in a certain direction. Previous to measurement, the spin is in a perfect superposition of the two eigenstates up and down.

The box in which the cat is hidden has two tiny slits. If the cat observes up, it sends a photon through the left slit. If it measures down, it sends a photon through the right slit. There is no other way for external observers to know what the cat measured.

The photon then travels out of the box toward a screen in the lab. No external measurement is performed that could determine from which slit the photon comes.

Do I observe interference on the screen?

Ciao

- viole

My answer is Yes.
But I will need some time to do the math and double-check.

 

[Polymath257]

This experiment is commonly done, although with light polarization instead of electron spin (and I'm sure the experiment with electron spin has been done, but I don'thave a reference).

Take light that is circularly polarized (corresponding to superposition of two linear polarizations), send it through a birefringent crystal to split the linear polarizations (measurement of polarization), send the two beams in different directions, recombine to send into a double slit experiment.

Unless there are other devices in one or both of the light paths, there will be interference. If, however, information on 'which path' is collected (which will absorb photons along one path or the other), the interference will disappear.

 

[Polymath257]

The basic issue is what happens to the electron, specifically after the 'measurement'. Does the measurement randomize the spin or not? If it does, then there is no interference pattern. If it does not randomize, then there will be. Also, if one spin or the other is absorbed, there will be no interference pattern.

So, at least part of the question is what sort of measurement you do and how is the result directed to the slits?

 

[viole]

The basic issue is what happens to the electron, specifically after the 'measurement'. Does the measurement randomize the spin or not? If it does, then there is no interference pattern. If it does not randomize, then there will be. Also, if one spin or the other is absorbed, there will be no interference pattern.

So, at least part of the question is what sort of measurement you do and how is the result directed to the slits?

If I am the cat, I would use an apparatus that measures the spin of that electron (and therefore I "collapse" its wave into up or down). If the apparatus tells me up, I press a switch that sends a photon through one slit. If the apparatus tells me down, then I press another button that fires a photon through the other.

The connection is done by my conscious brain once I read the value on the apparatus. Otherwise, the electron and the photon are not directly or physically connected.

Ciao

- viole

 

[Polymath257]

If I am the cat, I would use an apparatus that measures the spin of that electron (and therefore I "collapse" its wave into up or down). If the apparatus tells me up, I press a switch that sends a photon through one slit. If the apparatus tells me down, then I press another button that fires a photon through the other.

The connection is done by my conscious brain once I read the value on the apparatus. Otherwise, the electron and the photon are not directly or physically connected.

Ciao

- viole

OK, so the slits are separated enough that you can decide which one to send an electron through? In that case, there won't be an interference pattern no matter what.

To get an interference pattern. The slits have to be closer than the wavelength of the electrons going through. otherwise, you have 'which path' information and no interference.

Also, pressing the switch decouples the original electron from the final one. Again, no interference.

 

[viole]

OK, so the slits are separated enough that you can decide which one to send an electron through? In that case, there won't be an interference pattern no matter what.

To get an interference pattern. The slits have to be closer than the wavelength of the electrons going through. otherwise, you have 'which path' information and no interference.

Also, pressing the switch decouples the original electron from the final one. Again, no interference.

Yes, I (the cat) have "which path information", but the people outside do not. So, from their point of view, if there is no interference, then the cat and its experience is in a definite state, even if they have no clue what that state might be. That would resolve the paradox in the direction or realism, at least for bigger things like cats.

In other words: the qubit up/down has become a classical bit for the people outside the box.

Or, going back to the original: the cat is definitely in one of the states dead or alive, even if it is not known which one.

In fact, in case of the original experiment, I could you use another sensor in the box that detects if the cat is dead or alive and drive the triggering of the photon depending on the reading. In that case, lack of interference, would prove that the cat is in a definitive state.

There is something I am missing here, I am not completely convinced.

Ciao

- viole

 

[Polymath257]

Yes, I (the cat) have "which path information", but the people outside do not. So, from their point of view, if there is no interference, then the cat and its experience is in a definite state, even if they have no clue what that state might be. That would resolve the paradox in the direction or realism, at least for bigger things like cats.

In other words: the qubit up/down has become a classical bit for the people outside the box.

Or, going back to the original: the cat is definitely in one of the states dead or alive, even if it is not known which one.

Ciao

- viole

The question is whether you can control which slit the electron(or photon) goes through. if you can, then the interference pattern will be destroyed. If not, and the 'which slit' information isn't something that can be determined, then there will be interference. You are, in this situation, just setting yourself up as an electron gun that sends random spins through the slit.

 

[viole]

The question is whether you can control which slit the electron(or photon) goes through. if you can, then the interference pattern will be destroyed. If not, and the 'which slit' information isn't something that can be determined, then there will be interference. You are, in this situation, just setting yourself up as an electron gun that sends random spins through the slit.

OK. But suppose that I am myself the cat, together with the electron I measured, in a superposition of states:

| cat observed up, spin up > (and fires left cannon)
| cat observed down, spin down > (and fires right cannon)

A sort of entanglement of both outcomes from my measurement. So, no collapse, like in the Multi World interpretation.

Still no interference?

Ciao

- viole

 

[David T]

This is a question for the physicists here. I am not, so I don't know the answer, even though I have a strong suspicion.
I would like to propose a more animal friendly variant of the Schrödinger cat thought experiment.

Suppose that the cat is a conscious experimenter that performs a measurement of the spin of an electron in a certain direction. Previous to measurement, the spin is in a perfect superposition of the two eigenstates up and down.

The box in which the cat is hidden has two tiny slits. If the cat observes up, it sends a photon through the left slit. If it measures down, it sends a photon through the right slit. There is no other way for external observers to know what the cat measured.

The photon then travels out of the box toward a screen in the lab. No external measurement is performed that could determine from which slit the photon comes.

Do I observe interference on the screen?

Ciao

- viole

It was originally created to mock the Copenhagen interpretation of QM which is nutty.

 

[Polymath257]

OK. But suppose that I am myself the cat, together with the electron I measured, in a superposition of states:

| cat observed up, spin up > (and fires left cannon)
| cat observed down, spin down > (and fires right cannon)

A sort of entanglement of both outcomes from my measurement. So, no collapse, like in the Multi World interpretation.

Still no interference?

Ciao

- viole

Going from observation to firing a cannon decouples the spin and so gives no interference. To give an interference, no 'which path' information can be derived *from outside*. If the slit can be chosen, then there is still 'which path' from outside because the slits are far enough apart to eliminate the pattern.

Remember that to actually get an interference pattern requires many electrons to go through the system *and* the slits have to be closer than the wavelength of the electrons. And if that happens, you lose 'which spin' information for the previous steps when you send the electrons through the slits because the slits are so close together.

So, you have two cases: either the slits are far enough apart that there can be no interference pattern, or they are close enough together that the spin information is lost. Once that information is lost, an interference pattern emerges.

Truthfully, the cat in this case is a red herring.

 

[viole]

Going from observation to firing a cannon decouples the spin and so gives no interference. To give an interference, no 'which path' information can be derived *from outside*. If the slit can be chosen, then there is still 'which path' from outside because the slits are far enough apart to eliminate the pattern.

Remember that to actually get an interference pattern requires many electrons to go through the system *and* the slits have to be closer than the wavelength of the electrons. And if that happens, you lose 'which spin' information for the previous steps when you send the electrons through the slits because the slits are so close together.

So, you have two cases: either the slits are far enough apart that there can be no interference pattern, or they are close enough together that the spin information is lost. Once that information is lost, an interference pattern emerges.

Truthfully, the cat in this case is a red herring.

Thanks, I have to ponder on this.

My motivation came after attending some QM course from Susskind. There he says that when we observe something, there is really no collapse of any wave function, we just get entangled with the particle we observed. We become part of the superposition. So, we end up with two macroscopic branches in a superposition of states, one for each possible outcome. For someone outside, what the box contains is still a qubit, and not a classical bit, even if the objects involved in the superposition are macroscopic.

But if that is true, then inside that box there are two different versions of the cat after spin observation, the one that observed up and the one that observed down. Both is a superposition, as long as we do not open the box and check (measure). And if both fire the cannon on different slits, then the beam should be a superposition of the beams coming from both slits, by extension.

Only if we measured what slit is used, we become also part of the entanglement. But if we do not, then I would expect to see an interference. I was wondering if this interpretation of QM could be testable. But it's clear that I am missing something.

Probably, I should stick with math

Ciao

- viole

 

[shunyadragon]

Interesting and I will follow this thread. One word of caution is this research is discriptive from the human perspectie and has limitations.

 

[godnotgod]

Both 'meow', and 'not-meow'.

 

[sayak83]

Thanks, I have to ponder on this.

My motivation came after attending some QM course from Susskind. There he says that when we observe something, there is really no collapse of any wave function, we just get entangled with the particle we observed. We become part of the superposition. So, we end up with two macroscopic branches in a superposition of states, one for each possible outcome. For someone outside, what the box contains is still a qubit, and not a classical bit, even if the objects involved in the superposition are macroscopic.

But if that is true, then inside that box there are two different versions of the cat after spin observation, the one that observed up and the one that observed down. Both is a superposition, as long as we do not open the box and check (measure). And if both fire the cannon on different slits, then the beam should be a superposition of the beams coming from both slits, by extension.

Only if we measured what slit is used, we become also part of the entanglement. But if we do not, then I would expect to see an interference. I was wondering if this interpretation of QM could be testable. But it's clear that I am missing something.

Probably, I should stick with math

Ciao

- viole

You are in Stanford?

 

[viole]

You are in Stanford?

Me? no

I live near Lucerne, in Switzerland. Dr. Susskind is gracious enough to post his courses on the Internet.

Ciao

- viole