Macroscopic Quantum Coherence & Macrorealism experiments

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Discussion Overview

The discussion revolves around experiments related to macroscopic quantum coherence and the concept of macrorealism, particularly focusing on whether macroscopic objects can exist in quantum superpositions and how they relate to classical physics. Participants explore various experimental approaches and theoretical implications within the realms of quantum mechanics and its interpretations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants mention the preparation of macroscopic Bose-Einstein condensates as evidence of macroscopic quantum coherence.
  • Superconductivity is cited as a classic example of macroscopic quantum coherence, with references to experiments like the SQUID experiment demonstrating superposition principles.
  • Questions arise regarding whether specific experiments have successfully placed macroscopic objects in superpositions of distinct states, such as the "dead cat, alive cat" analogy.
  • Participants discuss the implications of various experiments, including those that challenge or support macrorealism, and the relevance of the Leggett-Garg inequality in this context.
  • There are references to ongoing experiments and articles that explore the boundaries between nonlinear and standard quantum mechanics, particularly concerning macroscopic objects.
  • Some participants express skepticism about the classification of certain experimental results as truly macroscopic, suggesting that the size and scale of objects involved may not meet the criteria for macroscopicity.
  • Discussions include the coherence achieved in mesoscopic systems and the challenges of achieving macroscopic superpositions, with references to specific experimental setups and their outcomes.

Areas of Agreement / Disagreement

Participants express a variety of views on the existence and implications of macroscopic quantum coherence. There is no clear consensus on whether certain experiments definitively demonstrate macroscopic superpositions, and the discussion remains unresolved regarding the definitions and criteria for macroscopicity in quantum experiments.

Contextual Notes

Participants note limitations in the current understanding of macroscopic quantum phenomena, including unresolved mathematical steps and the dependence on specific definitions of macroscopicity and coherence. Some references to articles and experiments are provided, but their acceptance within the community appears to vary.

StevieTNZ
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Has anyone performed experiments regarding macroscopic quantum coherence (superposition of and macroscopic object)?

What about testing if macroscopic objects obey macrorealism, or whether QM prevails?

Links to articles or experiments would be apprecited.
 
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I have no link at hand but I think macroscopic Bose-Einstein condensates have been prepared.
 
Superconductivity is a classic example of macroscopic quantum coherence.
 
StevieTNZ said:
Has anyone performed experiments regarding macroscopic quantum coherence (superposition of and macroscopic object)?

What about testing if macroscopic objects obey macrorealism, or whether QM prevails?

Links to articles or experiments would be apprecited.


yoda jedi said:
on: Quantum Superposition & Philosophy
Nov27-10

StevieTNZ said:
There was an interesting article published by Nature earlier this year entitled 'No Moon There'. You can read it here: http://www.engr.ucr.edu/~korotkov/news/2010-NatPhys.pdf


i read it, time ago.
i waiting the result on more big object like:

http://www.fqxi.org/community/articles/display/103 -> ONGOING EXPERIMENT
Aspelmeyer, Schwab, and Zeilinger !

it will elucidate too between:
NONLINEAR QUANTUM MECHANICS or STANDARD QUANTUM MECHANICS.
(Self Induced Collapses and Collapse of the Wavefunction on Macroscopic Object).

AND before that:

http://www.nature.com/nature/journal/v464/n7289/full/nature08967.html
Nature 464, 697-703 (1 April 2010)
 
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So, just to clarify, there has be an example of a macroscopic object being placed in a superposition of two distinct states (e.g. dead cat, alive cat)? Would that macroscopic object have just one wavefunction representing it?
 
In Ecole Normale Superieur there has been several experiments that implemented quantum superposition at a mesoscopic level. The system used was the field inside a superconducting (high Q) cavity. The duration of the photon inside the cavity was of the order of 10^(-2) second.

But there was another work, I tried to recover it from http://arxiv.org but I coudn't, All I remember is that the author succeded in obtaining coherence from two bottles of gas at room temperature. As his paper was not so commented after the publication, it seems that it was not so well accpeted by the community.

Best wishes

DaTario
 
StevieTNZ said:
http://www.nature.com/news/2010/100317/full/news.2010.130.html

Would that be an example of a macroscopic object being in two distinct macroscopic states?

I think it surely qualifies as a macroscopic object. There is also good evidence that it is in a superposition of two distinct states. But the distance between those states is less than the size of a proton in one direction. I would not call that macroscopic.
Just my two cents worth.
Jim Graber
 
I wonder actually if the experiment mentioned in http://www.engr.ucr.edu/~korotkov/news/2010-NatPhys.pdf takes into account the loophole mentioned in http://mcgill.academia.edu/MarkWild...phole_In_a_Leggett-Garg_Test_of_Macrorealism?

A violation of macrorealism (or even simply the Leggett-Garg inequality) would imply superposition of states wouldn't it? I was reading in 'Sneaking a Look at God's Cards' and the author mentions that although Leggett thought macrorealism implied noninvasive measurement, a contrary answer was given saying the two propositions are logically independent from each other. However, this does not change the final inequality that is a result from combining the two premises.
 
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  • #10
StevieTNZ said:
So, just to clarify, there has be an example of a macroscopic object being placed in a superposition of two distinct states (e.g. dead cat, alive cat)? Would that macroscopic object have just one wavefunction representing it?

Check out the Delft[1]/Stony Brook[2] SQUID experiment, where up to 10^11 particles exhibited the superposition principle.

And has been mentioned, superconductivity is the clearest manifestation, at the macroscopic scale, of quantum coherence. That's why experiments exhibiting macroscopic quantum phenomena are typically done using superconductivity, thus, the SQUID experiment mentioned above.

Zz.

[1] C.H. van der Wal et al., Science v.290, p.773 (2000).
[2] J.R. Friedman et al., Nature v.406, p.43 (2000).[ArXiv version http://arxiv.org/abs/cond-mat/0004293" ]
 
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  • #12
https://www.physicsforums.com/showthread.php?p=3006265#post3006265

another...

Large Quantum Superpositions and Interference of Massive Nano-objects.
http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.4081v1.pdf

..."objective collapse models of the wave function"...



-------------
http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.1236v1.pdf


-------------
it will elucidate between:
NONLINEAR QUANTUM MECHANICS or STANDARD QUANTUM MECHANICS.
(Self Induced Collapses and Collapse of the Wavefunction on Macroscopic Object).
CSL models and others.




.
 
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  • #14
Saw the 430 atom molecule interference article on www.quantum.at

Still wanting results for the superposition of the mirror. ;)
 
  • #15
StevieTNZ said:
Saw the 430 atom molecule interference article on www.quantum.at

Still wanting results for the superposition of the mirror. ;)

much better here:

http://www.univie.ac.at/qfp/publications3/pdffiles/ncomms1263.pdf



----------
has to be around 10 14 atoms.

also waiting...





.
 

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