The Significance of Decoherence in the Quantum-to-Classical Transition

[kexue]

I read often that the transition from quantum to classical, the fact that there normally no macroscopic quantum objects are observed, has only become clear with the proper understanding of the decoherence mechanism.

But what about Broglie wavelength!? Physicists knew before, that macroscopic objects do not show ( or are very very unlikely to show) quantum behavior such as interference or tunneling due to Broglie wavelength, since momentum of big object make Broglie wavelength negligibly small.

So am I right to assume that the problem of quantum-to-classical transition before decoherence explanations was not about position and momentum, but strictly about finite dimensional superposition, like a|alive> + b|dead>?

thank you

 

[ZapperZ]

This may not be true. The SIZE has nothing to do with it. The Stony Brook/Delft experiments has shown quantum effects for 10^11 particles. There's nothing, in principle, to prevent us from getting a mesoscopic, or even a macroscopic quantum object based on this.

The issue here is the ability to maintain coherence, not only for a large enough length scale, but also for a long enough time. This isn't easy and remains the biggest challenge.

Zz.

 

[kexue]

But what about the issue of the Broglie wavelength of this 10¯11 particle 'object'? It has to be kept small, too, right?

Also let me rephrase my original post

- "Traditional QM" says: interference, tunneling, noticeable uncertainty for macroscopic objects is extremely unlikely, due to Broglie wavelength and the uncertainty relations, since momentum of macroscopic objects is so big. "Decoherence QM" says it is not only unlikely, it is in principle impossible, due to decoherence. Only if coherence is maintained, it can happen.

-"Traditional QM" says: there is the Schrödinger cat problem, with a only two dimensional superpostion, that makes makes transition from quantum to classical possible (no small Broglie wave here), although it is never observed."Decoherence QM" says no Schrödinger cats, since decoherence.

What I just wrote is that somewhat correct?

 

[ZapperZ]

But what about the issue of the Broglie wavelength of this 10¯11 particle 'object'? It has to be kept small, too, right?

the deBroglie wavelength doesn't apply to that Stony Brook/Delft experiment. They are in a superconducting state in which 10^11 particles are in coherence with each other. We are not talking about some free particle floating around at some momentum.

Zz.

 

[kexue]

Thanks Zz. I just ordered the book of Schlosshauer on decoherence. After I read it I come back maybe with more question.

Why have Zurek, Zeilinger not won the Nobel price yet?

 

[fleem]

As Feynman once (allegedly) quipped, "nothing is classical". Certainly our world we be quite different if it were. Of course, I know your question is more, "Is there ~direct~ macroscopic evidence of de Broglie wavelength?"

Maybe quantum vortices? Not exactly 'direct' evidence but kinda close.

 

[f95toli]

Why have Zurek, Zeilinger not won the Nobel price yet?

Maybe because they haven't done anything that is significant enough to deserve one?

Don't get me wrong, both of them have contributed a lot to the debate over the measurement problem etc. However, despite what some may think they not "invent" the concept of decoherence etc; that has been around for a very long time (the obvious example being NMR).

The theories we use today were worked out by other people, some of which HAVE won the Nobel prize (albeit for other things), perhaps the most obvious examples being Bloch and Leggett.

 

[ZapperZ]

Maybe because they haven't done anything that is significant enough to deserve one?

Don't get me wrong, both of them have contributed a lot to the debate over the measurement problem etc. However, despite what some may think they not "invent" the concept of decoherence etc; that has been around for a very long time (the obvious example being NMR).

The theories we use today were worked out by other people, some of which HAVE won the Nobel prize (albeit for other things), perhaps the most obvious examples being Bloch and Leggett.

I think Zeilinger has done enough to warrant the Nobel Prize. He has certainly produced enough advancement on the EPR-type experiments for it to be well-verified. So I definitely will not be surprised if he gets it.

Zz.