Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Phonons and classical non-locality?

  1. Aug 28, 2015 #1
    I just discovered the concept of phonons and the story of Brian Josephson (from reading "Sync" by Steven Strogatz).

    What the h....?

    So Phonon's are collective excitations of classical stuff made from QM ensembles, excitations made possible by the QM properties of the ensemble members? Are phonons not examples of non-local entanglement at classical scales?

    Can an ensemble of phonons have "collective excitations"?

    Does phonon evolution require collapse-like measurements, or preclude them, or i don't know, somehow absorb or erase them?
  2. jcsd
  3. Aug 28, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    Phonons are quantized sound waves just like photons are quantized light waves.

    Just as pairs or groups of photons can be entangled with one another, so can pairs/groups of phonons.

    In principle. it is definitely possible to have quantum entanglement occur at the macroscopic scale.
    See for example:

    We don't necessarily see it all the time because quantum behavior is usually hard to observe outside the laboratory, where we can isolate the object we're looking at from outside disturbances.
  4. Aug 28, 2015 #3
    Very readable paper. And an elegant experiment. I also liked the paragraph at the end about the back propagation of the measurement projection to avoid the retro-causality GR-frame issue. I finally sort of got that argument. If I understand correctly the idea is that there is literally nothing available inside the quantum, meaning inside the interval between the detector d and the moment of scattering. Therefore all "projections of measurement" relate to the state at the moment of scattering.

    That said, the non-local (space-like) coherence of the phonon across the two diamonds is plenty bizzare? That's what that is right?

    The part I just can't shake is how a system going from state to state in the non-equilibrium case doesn't play some version of this same game. The experiment is about a controlled exposure of the phenomenon through an extraordinary manipulation of entropy and disequilibrium, but doesn't the result potentially show a fundamental mechanism of everyday quantum chemistry? Are phonons a part of the understanding of microscopic material elasticity? I feel like the gap between QM and chemistry is an absolute blank, in my mind.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook