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Superfluidity is briefly mentioned in the article, but it's a quantum effect that's visible in very large systems. A system exhibits zero viscosity when its pa

Superfluidity is briefly mentioned in the article, but it's a quantum effect that's visible in very large systems. A system exhibits zero viscosity when its particles condense into a single quantum mechanical state. Superconductivity is an instance of this, where electrons pair up and flow without resistance. Buckets of liquid helium show superfluidity. [1] Labs cool blobs of alkali gas to superfluidity. [2] Entire cores of neutron stars are superfluid. [3] There's even a theory of quantum gravity where physical vacuum is a superfluid. [4] [1] https://www.youtube.com/watch?v=2Z6UJbwxBZI https://www.youtube.com/watch?v=2Z6UJbwxBZI [2] https://www.youtube.com/watch?v=1RpLOKqTcSk https://www.youtube.com/watch?v=1RpLOKqTcSk [3] http://arxiv.org/abs/1012.0045 http://arxiv.org/abs/1012.0045 [4] https://en.wikipedia.org/wiki/Superfluid_vacuum_theory https://en.wikipedia.org/wiki/Superfluid_vacuum_theory

jessriedel 11y ago
This isn't really more "macroscopically quantum" than spectroscopy or the stability of matter. (Neither of those would be possible in a normal classical universe either.) You're just noticing indirect quantum effects on large scales, but there is no macroscopic coherence. On the other hand, the interferometery experiments like MAQRO discussed in the article do actually exhibit long-range coherence of large amounts of matter.
- biswaroop 11y ago
  Although liquid helium is kind of a partial BEC, isn't a BEC one of the best examples of a coherent state? Except for certain quantum phase liquids, superfluid systems often exhibit long-range phase coherence. I'd actually be curious to know the quantum discord of a superfluid Fermi gas.
  - jessriedel 11y ago
    No, the spatial coherence of a BEC isn't larger than the ground state wavefunction.
theophrastus 11y ago
At that rate isn't superconductivity a "quantum effect"? If electron orbital transitions are governed by quantum effects, what common phenomenon isn't a quantum effect? I know of a biochemistry lab cohort which would be deeply offended if photosynthesis wasn't classified as a quantum effect.
Florin_Andrei 11y ago
> a quantum effect that's visible in very large systems Well, in a certain sense, chemistry and solid state, and the very existence of atoms are also macroscopically-visible quantum phenomena. You do a science class with kids in school and show them static electricity, little pieces of paper dancing in an electric field - that's quantum. That's electric fields interacting, which is an exchange of virtual photons, which is a quantum phenomenon. We really are jut waves on the surface of an ocean of quantum phenomena.

jessriedel 11y ago

This isn't really more "macroscopically quantum" than spectroscopy or the stability of matter. (Neither of those would be possible in a normal classical universe either.) You're just noticing indirect quantum effects on large scales, but there is no macroscopic coherence. On the other hand, the interferometery experiments like MAQRO discussed in the article do actually exhibit long-range coherence of large amounts of matter.

biswaroop 11y ago
Although liquid helium is kind of a partial BEC, isn't a BEC one of the best examples of a coherent state? Except for certain quantum phase liquids, superfluid systems often exhibit long-range phase coherence. I'd actually be curious to know the quantum discord of a superfluid Fermi gas.
- jessriedel 11y ago
  No, the spatial coherence of a BEC isn't larger than the ground state wavefunction.

theophrastus 11y ago

At that rate isn't superconductivity a "quantum effect"? If electron orbital transitions are governed by quantum effects, what common phenomenon isn't a quantum effect? I know of a biochemistry lab cohort which would be deeply offended if photosynthesis wasn't classified as a quantum effect.

Florin_Andrei 11y ago

> a quantum effect that's visible in very large systems Well, in a certain sense, chemistry and solid state, and the very existence of atoms are also macroscopically-visible quantum phenomena. You do a science class with kids in school and show them static electricity, little pieces of paper dancing in an electric field - that's quantum. That's electric fields interacting, which is an exchange of virtual photons, which is a quantum phenomenon. We really are jut waves on the surface of an ocean of quantum phenomena.