Quantum tunnelling - what is real?

[ZapperZ]

That link does not work. You may have mentioned previously it in another thread, but not this one before #20. Is there a link somewhere for it somewhere else? Thanks.

There's no link. You will have to find access to Phys. Rev. papers.

Zz.

 

[George Jones]

That link does not work.

ZapperZ ddn't give a link! He gave a reference to an journal, W.A. Harrison,Phys. Rev.123, 85 (1961)! In this instant internet age, have we forgotten what this means!

If you are a student, you probably have a number of ways that you can access this.

1) Go to your university library, and find a (bound) hardcopy, and, if it looks interesting, photocopy it, or scan it.

2) Go to your library, and, on a library computer, get a pdf file of the article using PROLA (Physical Review Online Archive).

3) You may be able to get articles at home using PROLA and your university account.

[edit]Zz was faster[/edit]

 

[Jilang]

ZapperZ ddn't give a link! He gave a reference to an journal, W.A. Harrison,Phys. Rev.123, 85 (1961)! In this instant internet age, have we forgotten what this means!

If you are a student, you probably have a number of ways that you can access this.

1) Go to your university library, and find a (bound) hardcopy, and, if it looks interesting, photocopy it, or scan it.

2) Go to your library, and, on a library computer, get a pdf file of the article using PROLA (Physical Review Online Archive).

3) You may be able to get articles at home using PROLA and your university account.

[edit]Zz was faster[/edit]

Thanks Mr Jones for your helpful advice (as always!). I found the site and created an account there, but I am not a student so would have to buy it. I don't live near a library either. Having read read the abstract I am not that much interested in how to calculate the wavefunction which is what it says it about, so am going to pass. Thanks again.

 

[ZapperZ]

Thanks Mr Jones for your helpful advice (as always!). I found the site and created an account there, but I am not a student so would have to buy it. I don't live near a library either. Having read read the abstract I am not that much interested in how to calculate the wavefunction which is what it says it about, so am going to pass. Thanks again.

But this is where the DETAILS are, and I thought that's what you're asking. Harrison (and the subsequent Bardeen's paper) gave explicit details of the description inside the barrier! That is what is means by such a calculation. If you bother to read it, you'll also notice the presence of the group velocity of the tunneling particle, which something that I had a very intimate knowledge of because I had to model that inside the barrier itself to match the experimental tunneling spectra as part of my doctoral work.

It is when you match experiment with the theoretical description are you able to make a convincing argument of the validity of ANY description, and this is what can be done regarding "what is going on" inside the barrier!

But besides this, there is a more general issue here, which is the "leakage" of the wavefunction inside a classically-forbidden region. There are many other phenomena beyond just tunneling where this is applicable, including the famous superconducting proximity effect. Here, we also can't "see" what is going on inside the "barrier" other than measuring the surface resistivity (did the superconducting order parameter actually leaked into a non-superconducting region?). But the theoretical description produced such accurate measurements of what you should get if this were to happen, that this phenomenon is a done deal as far as establishing its validity.

So to me, this question really isn't about "what's going on inside the barrier". But rather, it is more on the reflection ON YOU on what really is your criteria of what you accept to be valid. There have been NO detectors put inside a tunneling barrier to detect the tunneling particle. Period. However, does that make the theoretical picture of what we have invalid and untested? Does that fact that we have OTHER experimental observations, of which the entire result produced a consistent result that agreed with such a picture, completely irrelevant to you?

Zz.

 

[Jilang]

So to me, this question really isn't about "what's going on inside the barrier". But rather, it is more on the reflection ON YOU on what really is your criteria of what you accept to be valid. There have been NO detectors put inside a tunneling barrier to detect the tunneling particle. Period. However, does that make the theoretical picture of what we have invalid and untested? Does that fact that we have OTHER experimental observations, of which the entire result produced a consistent result that agreed with such a picture, completely irrelevant to you?

Zz.

I don't know how you got the impression that that I am questioning the validity of any experiment. I am becoming more inclined to believe that you did not really grasp the direction of my initial question. You state that no detectors have been out inside a tunnelling barrier to detect the tunnelling particle. That is useful information thank you. But would it be ever possible to? I am now thinking probably not.

 

[ZapperZ]

I don't know how you got the impression that that I am questioning the validity of any experiment. I am becoming more inclined to believe that you did not really grasp the direction of my initial question. You state that no detectors have been out inside a tunnelling barrier to detect the tunnelling particle. That is useful information thank you. But would it be ever possible to? I am now thinking probably not.

And I don't think you really grasp what I've been trying to tell you all along!

Your original question, if you look at it again, seemed to question "what is real" as far as what goes on inside the barrier. It was as if it is a requirement that there needs to be some 'detector' inside the barrier for there to be ANY acceptance of any validity of the physics in there.

I argued that we have OTHER MEANS of knowing what goes on in there. I gave you an example of adding magnetic impurities to superconducting tunnel junctions, where magnetic impurities inside the barrier can have a strong effect, just as expected and predicted, on the tunneling spectrum. I argued that the agreement between theory and experiment is ONE way we can measure what goes on inside the barrier. I also argue that this technique is essentially what we have been doing all along in understanding and verifying ALL of our observations.

That is why I do not understand why there is this issue that we don't know what is going on inside the barrier, considering that there is no issue on what is going on elsewhere in the tunneling process.

Zz.

 

[anorlunda]

Professor Susskind touched on this question in one of his lectures. He said that if you calculate the minimum energy required to detect the particle inside the barrier, the answer is exactly the same energy needed to lift the particle over the barrier without tunneling. That would leave you with a paradoxical result; did it tunnel or not?

That is the end result of all experiments that try to peer into the inner workings of quantum mechanics to see more details than quantum mechanical mathematics tell. They all fail. That is not intuitive or satisfying, but it is true.

 

[Jilang]

And I don't think you really grasp what I've been trying to tell you all along!

Your original question, if you look at it again, seemed to question "what is real" as far as what goes on inside the barrier.

Zz.

I don't think you read past the title of the thread. I was asking if the existence of a non vanishing wavefunction would lead to any chance of it actually being found there.

 

[Jilang]

Professor Susskind touched on this question in one of his lectures. He said that if you calculate the minimum energy required to detect the particle inside the barrier, the answer is exactly the same energy needed to lift the particle over the barrier without tunneling. That would leave you with a paradoxical result; did it tunnel or not?

That is the end result of all experiments that try to peer into the inner workings of quantum mechanics to see more details than quantum mechanical mathematics tell. They all fail. That is not intuitive or satisfying, but it is true.

Thanks Anorlunda, that ties in with what the guys at Toronto concluded (see post #18).

 

[ZapperZ]

I don't think you read past the title of the thread. I was asking if the existence of a non vanishing wavefunction would lead to any chance of it actually being found there.

... and what did you think I've been trying to show you all along? This leads me to believe that you really haven't understood the magnetic impurity discussion.

I think I'm done here.

Zz.

 

[Jilang]

... and what did you think I've been trying to show you all along? This leads me to believe that you really haven't understood the magnetic impurity discussion.

I think I'm done here.

Zz.

Thanks Zzz, I do appreciate your input.