Quantum mechanics for big things?

[kith]

What is not clear is why a large body would display quantum behavior in broad daylight in front of recording equipment without observable decoherence setting in with a rapid return to classicality

Decoherence happens in a certain basis. It doesn't restrict the populations of these basis states. In particular, there's no problem with all particles occupying the same state.

These populations are given by the statistics. There are many examples of quantum effects for macroscopic systems which are due to quantum statistics: lasers, semiconductors, neutron stars, superconductivity, superfluidity, etc. Even the volume of ordinary bulk matter could be dubbed a quantum effect.

 

[jarekd]

your opinion, because this is the consensus in the physics comunnity

Not only mine, also for example of reviewers from Phys. Rev. Let. as the abstract is "We have observed quantum interference of vortices in a Josephson-junction array. When vortices cross the array along a doubly connected path, the resultant resistance oscillates periodically with an induced charge enclosed by the path. This phenomenon is a manifestation of the Aharonov-Casher effect. The period of oscillation corresponds to the single electron charge due to tunneling of quasiparticles."

I think your problem is the question of what is the de Broglie's clock - for fluxons this conjugated internal periodic dynamics has a bit different nature than for electrons or photons ... but in the http://www.univie.ac.at/qfp/publications3/pdffiles/ncomms1263.pdf, in abstract they write that de Broglie's wavelength here is lambda=h/mv~1pm, while later they have oscillations with wavelengths of hundreds of nanometers - I doubt it is the same de Broglie's clock as for photons or electrons - it is rather of some effective vibrations of the whole molecule.

And if we allow for any, also effective de Brogle's clock, not only we can classify fluxons for quantum interference, but also macroscopic Couder's walking droplets in double-slit experiment: http://prl.aps.org/abstract/PRL/v97/i15/e154101

Can we go even larger? Maybe celestial bodies? :) They usually have internal periodic process: rotation, what can work as de Broglie's clock ... but for interference we need also a medium carrying waves from this periodic process, such that these waves could later affect behavior of the object which created them - maybe interference of some pulsar, using gravity waves and ... a few million years :)

However, maybe we could look for a more serious "quantum-like" properties on statistical level as there is some resemblance with Bohr's atomic model. If we would average millions of years of relative position of e.g. a planet, there are plenty of looking randomly disturbances from perfect trajectory - like caused by gravity of other planets. So to predict such time average, we should use some thermodynamical model, like taking Boltzmann distribution among all paths it could travel through - exactly like in euclidean path integral formulation of quantum mechanics, it should lead to quantum statistics of this averaged positions - discussion: https://www.physicsforums.com/showthread.php?t=710790

 

[StevieTNZ]

correlation is not entanglement.

I don't quite understand how this statement has anything to do with the diamonds entangled.

 

[Vanadium 50]

liquid helium is a new entirely classical behavior due to quantum effects

Those words make no sense in that order. Behavior cannot be entirely classical if due to quantum effects. It's like talking about the corners of a circle.

 

[.Scott]

The biggest quantum effect that I recall occurs at event horizons, for example, the event horizon of a black hole.
Viewed from the outside, an object falling into a black hole will never quite make it to the event horizon. Instead, an extreme case of time dilation will be observed. So if a watch crosses the horizon at noon, we will see the watch approach noon but never reach it.

Here's where QM takes over. Under these conditions, Heisenberg Uncertainty takes over. When we can see the watch so precisely in time, it is not possible for us to know as much about its location. As a result, the watch will blur into a holographic pattern that will soon cover the entire surface of the black hole.

You can also create an event horizon by maintaining a constant acceleration. From your non-inertial reference frame, an event horizon will follow behind you with this same QM holographic affect. That QM effect will separate you from approximately half the universe.

 

[jarekd]

Scott, sure the (looking self-contradictory) hypothesized Hawking radiation is a quantum phenomena, but like Pauli exclusion principle in white dwarfs, it is not "for big things" but regards the microscopical ones ... just in presence of "a big thing".

 

[Maui]

Those words make no sense in that order. Behavior cannot be entirely classical if due to quantum effects. It's like talking about the corners of a circle.

The monitor of my computer is an entirely classical behavior of quantum fields and 'particles'. The superfluid liquid helium seems like a new classical phenomena that can only be explained(at this time?) via quantum theory. Just like temperature is explained by the motion of atoms and molecules but is not a quantum phenomenon(it's strictly classical).

 

[.Scott]

Scott, sure the (looking self-contradictory) hypothesized Hawking radiation is a quantum phenomena, but like Pauli exclusion principle in white dwarfs, it is not "for big things" but regards the microscopical ones ... just in presence of "a big thing".

I wasn't referring to Hawking radiation. I was referring to the hologram that are created as material crosses the event horizon. It comprises the entire event horizon - although it is very thin.

 

[audioloop]

I don't quite understand how this statement has anything to do with the diamonds entangled.

one thing is quantum correlation (coherence) and other is entanglement.
the effect cited by you, has been observed time ago before this one.

read
Chen, H., et. al., 2011. Observations of anti- correlations in incoherent thermal light fields. Phys. Rev. A. 84: 033835.

and from brezinski
http://www.hindawi.com/journals/jamp/2012/469043/

"The recent paper entitled by K. C. Lee et al. (2011) establishes nonlocal macroscopic quantum correlations, which they term “entanglement”, under ambient conditions. Photon(s)-phonon entanglements are established within each interferometer arm. However, our analysis demonstrates, the phonon fields between arms become correlated as a result of single-photon wavepacket path indistinguishability, not true nonlocal entanglement"

 

[audioloop]

"Our analysis is that Lee’s explanation, in the Science paper, for the quantum correlations generated between diamonds (resulting from the pump photons) is unlikely representative of the actual situation. They postulated a nonlocal entanglement between the diamonds. While we agree that quantum correlations are established, we do not believe that the data or analysis of the experimental design supports true entanglement. The essential points will be made here but the remainder of the paper will expand on these points. First, our examination supports that these nonlocal quantum correlations occur from a combination of paths indistinguishability (for a single photon wavepacket) plus nearly identical local entanglements (Raman scatterers) in each path [13–19]. The source is coherent so building the pulses up from single photon wavepackets (a photon can only interfere with itself) is a useful approach for illustrating the physics. The correlations between diamond phonons do not fit definitions of entanglement laid out, for example, by von Neumann, EPR-B, or GHZ"

 

[StevieTNZ]

I've contacted one of the authors of the diamond paper with regards to the paper you link, to get his view on it.

 

[Maui]

Decoherence happens in a certain basis. It doesn't restrict the populations of these basis states. In particular, there's no problem with all particles occupying the same state.

Correct me if I am wrong but they do not occupy the same state but a joint state similar to the joint state of entangled particles where even the slightest disturbance breaks the joint quantum state. Obviously in the superfluid helium somehow it does not.

These populations are given by the statistics. There are many examples of quantum effects for macroscopic systems which are due to quantum statistics: lasers, semiconductors, neutron stars, superconductivity, superfluidity, etc. Even the volume of ordinary bulk matter could be dubbed a quantum effect.

But have quantum statistics been directly observed so far or not? I don't think so. Not once. The effects you list all happen in a non measuring environment at scales impossible to observe directly and had there been a particularly accurate position or momentum measurement the devices likely wouldn't work as intended.

Besides, singling out a preferred basis means you are already observing classical (-like) behavior not quantum.

 

[Vanadium 50]

Maui,

Enough. Our mission is to provide a place for people (whether students, professional scientists, or others interested in science) to learn and discuss science as it is currently generally understood and practiced by the professional scientific community. Denying superfluidity is a quantum mechanical phenomena does not meet this standard. Indeed, this doesn't even meet the Wikipedia standard - the second sentence of http://en.wikipedia.org/wiki/Macroscopic_quantum_phenomena is "However, at low temperatures, there are phenomena that are manifestations of quantum mechanics on a macroscopic scale, the best-known being superfluidity and superconductivity."

Enough.

 

[jarekd]

Vanadium, I think the issue here is finding the boundary between classical and quantum world. I was trying to find it for many years, but if by "classical" we mean not just "classical mechanics", but "classical field theory" - I honestly couldn't find any boundary.
For example Coulder's walking droplets show how to see interference, tunneling, orbit quantization ... maximal entropy random walk shows that after repairing approximation of maximizing uncertainty, stochastic models are no longer in disagreement with quantum predictions, "squares" leading to violation of Bell inequities are natural for stochastics in 4D spacetime ... soliton particle models is a natural way to handle varying number of interacting particles ...

Where exactly is the boundary?

 

[Maui]

http://en.wikipedia.org/wiki/Macroscopic_quantum_phenomena is "However, at low temperatures, there are phenomena that are manifestations of quantum mechanics on a macroscopic scale, the best-known being superfluidity and superconductivity."

Enough.

I am in complete agreement with the wording. That concludes my participation in the thread.

 

[jarekd]

bhobba, sure everything can be seen from quantum perspective ... but is there anything what cannot be also seen from classical field theory perspective?

Like coupled pendulums - we can see them "classically" as just two moving balls, or through their normal modes, where the coordinates just rotate - we have "quantum" unitary evolution.
Going to infinite number of coupled pendulums, we can again see a crystal "classically": through dynamics of every atom ... or through e.g. phonons, collective excitations evolving in "quantum" unitary way.
Now taking infinitesimal limit, we can see it as a classical field theory ... or make its quantization, like operating on Feynman diagrams where particles have structure: are solitons ...

Why "classical" and "quantum" are not just two different perspectives on the same system?

 

[bhobba]

Why "classical" and "quantum" are not just two different perspectives on the same system?

I deleted my post because I realized you were talking about something different than an initial reading of your post indicated.

But in so far as QM can be derived from classical like principles the answer depends on what you mean by classical like.

Thanks
Bill

 

[bhobba]

Gave the paper a quick squiz. Not my cup of tea and don't agree with any of it.

But just one question out of many - why do you consider i (the square root of minus 1) paradoxical? It simply represents a rotation through 90% in the complex plane - its no more paradoxical than say -1 itself, which represents a rotation through 180%.

Its importance in QM is it allows the introduction of phase so you get path cancellation in Feynmans sum over histories. There are others as well such as complex spaces are required for Wigners theorem to apply. Its got nothing to do with paradox - its got to do with what required to model QM phenomena - like its used in many other areas of applied math.

Thanks
Bill

 

[bhobba]

No, quantum mechanics is not about an observer - it is something very objective.

That's just one of many many issues it has. I was going to mention that one but chose his views about complex numbers instead.

Thanks
Bill

 

[jarekd]

bhobba, indeed the complex numbers are from one side a natural mathematical tool to operate on any periodic processes.
Another place we use them in quantum mechanics is the Wick rotation to "imaginary time", which corresponds just to the Legendre transform: changing sign in kinetic term while getting from Hamiltonian to Lagrangian density (I have written about it here).

 

[BOAS]

Bose-Einstein condensates allow us to look at quantum effects at the macroscopic scale.

 

[bhobba]

Another place we use them in quantum mechanics is the Wick rotation to "imaginary time", which corresponds just to the Legendre transform: changing sign in kinetic term while getting from Hamiltonian to Lagrangian density

Its really the same thing. With a Wick rotation of the propagator you get a standard Wiener process and of course conversely. This is a very very interesting fact but its deep significance is again what Feynman figured out - particles take all paths but because of complex numbers only those of stationary action do not cancel.

Mathematically its required as well to rigorously define the path integral which can be done by the generalization of Wiener processes called Hida Distributions.

Thanks
Bill

 

[kith]

bhobba, sure everything can be seen from quantum perspective ... but is there anything what cannot be also seen from classical field theory perspective?

https://en.wikipedia.org/wiki/Photon_antibunching

 

[kith]

Correct me if I am wrong but they do not occupy the same state but a joint state similar to the joint state of entangled particles where even the slightest disturbance breaks the joint quantum state. Obviously in the superfluid helium somehow it does not.

Yes and that's a very fundamental property of systems with identical particles: their states have to be symmetric or antisymmetric under particle exchange. "Breaking" such a joint state is not possible because the resulting state wouldn't have the right symmetry.

As far as classical behaviour is concerned, you seem to define it via decoherence. This doesn't make sense. A phenomenon is "classical" if it can be explained by classical mechanics. Decoherence shows how classical mechanics emerges from QM. This doesn't say anything about the existence of genuine quantum effects which can not be explained by classical mechanics. If there were none, we wouldn't need QM in the first place.

 

[jarekd]

Bhobba, the Wick rotation between Boltzmann/euclidean and Feynman ensemble among paths can be indeed related with adding the wave nature - internal periodic process of particles.
It has the essence of wave-corpuscle duality: it is going from thermodynamics of a point particle (after some small correction it can be seen as stochastic modeling) to seeing them only through their wave nature.
But alternatively it can also be seen as going from Hamiltonian (we have energy in Boltzmann ensemble) to action (we have Lagrangian in Feynman ensemble). This Legendre transformation is best seen in the field formulation.

This is the problem of understanding quantum mechanics - it uses simple universal mathematical tools, leaving place for lots of sophisticated connections, interpretations ... blurring the real physics behind this abstract mathematical tool.
If we really want to understand it, we need to start there - try to see the underlying physics below first and then quantum description emerging from it.

Kith, I don't understand why you have pointed photon antibunching?
Sure, we honestly don't understand photons, dynamics behind their production ... but it is mainly because orthodox quantum mechanics claims that we shouldn't even try to understand this kind of structures/dynamics.
Why are suggesting that it cannot be understood from one of these perspectives?

 

[kith]

Kith, I don't understand why you have pointed photon antibunching? [...] Why are suggesting that it cannot be understood from one of these perspectives?

Do you disagree with the argument given in the wikipedia-link? (I don't have access to better sources at the moment but the claim that antibunching is not explainable classicaly is widely accepted in the quantum optics community)

"If the field had a classical stochastic process underlying it, say a positive definite probability distribution for photon number, the variance would have to be greater than or equal to the mean. This can be shown by an application of the Cauchy-Schwarz inequality to the definition of g^{(2)}(0). Sub-Poissonian fields violate this, and hence are nonclassical in the sense that there can be no underlying positive definite probability distribution for photon number (or intensity)."

Also this gets a bit off topic.

 

[jarekd]

kith, antibunching means that they are more uniformly distributed.
Sure if atoms would be independent, you would expect less uniform: Poisson distribution ... so you only say that they are not independent - that there are some interactions between them, some kind of synchronization ... why these interactions have to be "non-classical" whatever it means?

Quantum mechanics has became kind of "intelligent project" type of argument - if we don't understand something, we can always say that "it is quantum" ... and problem solved.
No it isn't - lack of understanding does not imply lack of real explanation ... and this "orthodox quantum"/"intelligent design" attitude only makes that people don't even try to search.

There are more and more deeper, intuitive understanding of processes believed to be not understandable, for example here is Feynman's quote about interference from his QM book:
« … In this chapter we shall tackle immediately the basic element of the mysterious behavior in its most strange form. We choose to examin a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which is at the heart of quantum mechanics. In reality it contains the only mystery. We cannot make the mystery go away by explaining how it works . We will just tell you how it works.… »
... while Couder has recently shown simple macroscopic "classical" (field theory) e.g. double-slit interference analogue which we can understand: https://www.physicsforums.com/showthread.php?t=550729

And the space of "quantum" in meaning "not-understandable" phenomenas is shrinking every year.
Photons is a tough problem as we don't have "classical" understanding of most related phenomenas - but from the quantum side we have just abstract descriptions - not understanding, but rather assumption that it works as it works.
I can talk a lot about photons - they carry just energy, momentum and angular momentum - what means that they can be understood: as twist-like waves of electromagnetic field, like behind marine propeller ... but it is not a place for this discussion ...

 

[Maui]

As far as classical behaviour is concerned, you seem to define it via decoherence. This doesn't make sense. A phenomenon is "classical" if it can be explained by classical mechanics. Decoherence shows how classical mechanics emerges from QM. This doesn't say anything about the existence of genuine quantum effects which can not be explained by classical mechanics. If there were none, we wouldn't need QM in the first place.

No, my definition of quantum behavior is observing directly or indirectly(post factum observation of) behavior that can only be explained in terms of wave like properties(e.g putting an object in its ground state). Obviously everything is quantum, but classical(and classical-like behavior) means that everything always reduces to particles in all experiments, whereas quantum behavior is what is supposed to be observed in superliquid helium and which I find hard to believe(the Wikipedia article seems to be contradiction with established science e.g. O'Connell, A. D. et al. Nature doi:10.1038/nature08967 - "Largest ever object put into quantum state".). The observed behavior of superliquid helium is said to not be reducible to particles although it's directly observed/measured and recorded. That's the crux of the argument.

PP. Vanadium, I just had to clarify my position as it seems it was misunderstood and I have no intention of arguing over it.

 

[kith]

Quantum mechanics has became kind of "intelligent project" type of argument - if we don't understand something, we can always say that "it is quantum" ... and problem solved.

Of course, it is justified to check how the formalism of QM can be explained from more fundamental principles. For example, there has been a lot of reasearch on the question "why do observers see random results?". We now have all kinds of different explanations: hidden variables, influences from the future, other worlds and so on.

But the problem with all of them is that the thing which is supposed to explain the random results, can not be observed in measurements even in principle. And QM suggests why this is so: any interaction leads to entanglement and in order to perform a measurement on a system, you have to interact with the system.

I don't say that QM is something like a final theory and I don't defend the orthodox interpretation. I just think it is very unlikely that more fundamental theories will get rid of this fundamental limit on empirical knowledge QM seems to demand.

But this starts to get really off topic. /edit: removed a statement which was too strong

 

[kith]

No, my definition of quantum behavior is observing directly or indirectly(post factum observation of) behavior that can only be explained in terms of wave like properties(e.g putting an object in its ground state).

And why should this be a sensible definition? After all, it includes classical electrodynamics. Why do you reject the obvious definition that quantum effects are effects which are only predicted by quantum mechanics but not by classical mechanics / electrodynamics?