5 ms·

tl;dr abstract of the paper: ---snip--- Abstract. Instabilities of equilibrium quantum mechanics are common and well-understood. They are manifested for examp

tl;dr abstract of the paper: ---snip--- Abstract. Instabilities of equilibrium quantum mechanics are common and well-understood. They are manifested for example in phase transitions, where a quantum system becomes so sensitive to perturbations that a symmetry can be spontaneously broken. Here, we consider the possibility that the time evolution governing quantum dynamics may be similarly subject to an instability, at which its unitarity spontaneously breaks down owing to an extreme sensitivity towards perturbations. We find that indeed such an instability exists, and we explore its immediate consequences. Interpretations of the results both in terms of extreme sensitivity to the influence of environmental degrees of freedom, and in terms of a possible fundamental violation of unitarity are discussed. ---snip--- Is this suggesting that quantum superpositions have a tendency to spontaneously collapse, or am I misreading it?

selimthegrim 11y ago
Uh, this isn't the abstract of that nature paper at all
- david-given 11y ago
  You're quite right. It's not. This is the correct abstract: ---snip--- Charge ordering in metals is a fundamental instability of the electron sea, occurring in a host of materials and often linked to other collective ground states such as superconductivity. What is difficult to parse, however, is whether the charge order originates among the itinerant electrons or whether it arises from the ionic lattice. Here we employ high-resolution X-ray diffraction, combined with high-pressure and low-temperature techniques and theoretical modelling, to trace the evolution of the ordering wavevector Q in charge and spin density wave systems at the approach to both thermal and quantum phase transitions. The non-monotonic behaviour of Q with pressure and the limiting sinusoidal form of the density wave point to the dominant role of the itinerant instability in the vicinity of the critical points, with little influence from the lattice. Fluctuations rather than disorder seem to disrupt coherence. ---snip--- So. What does this mean in English? Also, can I downvote my own posts?
  - anigbrowl 11y ago
    It is a dense and difficult paper. I've made 5 attempts to summarize what I think they're saying and deleted them all, which is a reflection of both my lack of understanding and the difficulty of the underlying concepts. As best I can make out, they're saying that electromagnetic phenomena depend more on chaotic subatomic processes than on the purity or exact configuration of a material's crystalline structure, and they know this because high-resolution observations at a range of temperatures and pressures correlate nicely with a particular set of theoretical predictions. This might be significant in that you could optimize for superconductivity by tuning the aggregate electromagnetic characteristics of a material rather than requiring hard-to-achieve structural uniformity at the molecular level.
    - selimthegrim 11y ago
      No, they're not subatomic. Charge density waves mean that there is a periodic modulation of charge (for a little more background, see the Quora answers here: http://www.quora.com/What-are-the-significances-of-charge-density-waves-CDW-and-spin-density-waves-SDW-in-condensed-matter-physics http://www.quora.com/What-are-the-significances-of-charge-de... and this pdf: http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/magnetism.pdf http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes... ) What they are saying is that itinerant electrons (those not localized in a given orbital, but which occupy bands throughout the metallic system and hop, in contrast to an standard insulating magnet) have the instability within themselves, the lattice does not necessarily need to give them a push (this is called "dynamically generated"). In my answer I go into a bit of detail about the heretofore standard role of the lattice as well as the applications to superconductivity. What this paper is saying is that the Peierls distortion (cf. answers cited or Wikipedia) in these systems is either paralleling or a consequence of the electronic instability. The bit about following the Q wave vector has to do with the discussion of "nesting" in the answers (that is, how well does the momentum of the electrons couple with that of the phonons/ionic lattice vibrations at a certain periodicity and do they steal energy away from the lattice leading to an overall lower state (and is this the _primary_ factor in that lowering, a conclusion this paper would seem to militate against)" A good reference on this is the book by Assa Auerbach "Interacting Electrons and Quantum Magnetism"

selimthegrim 11y ago

Uh, this isn't the abstract of that nature paper at all

david-given 11y ago
You're quite right. It's not. This is the correct abstract: ---snip--- Charge ordering in metals is a fundamental instability of the electron sea, occurring in a host of materials and often linked to other collective ground states such as superconductivity. What is difficult to parse, however, is whether the charge order originates among the itinerant electrons or whether it arises from the ionic lattice. Here we employ high-resolution X-ray diffraction, combined with high-pressure and low-temperature techniques and theoretical modelling, to trace the evolution of the ordering wavevector Q in charge and spin density wave systems at the approach to both thermal and quantum phase transitions. The non-monotonic behaviour of Q with pressure and the limiting sinusoidal form of the density wave point to the dominant role of the itinerant instability in the vicinity of the critical points, with little influence from the lattice. Fluctuations rather than disorder seem to disrupt coherence. ---snip--- So. What does this mean in English? Also, can I downvote my own posts?
- anigbrowl 11y ago
  It is a dense and difficult paper. I've made 5 attempts to summarize what I think they're saying and deleted them all, which is a reflection of both my lack of understanding and the difficulty of the underlying concepts. As best I can make out, they're saying that electromagnetic phenomena depend more on chaotic subatomic processes than on the purity or exact configuration of a material's crystalline structure, and they know this because high-resolution observations at a range of temperatures and pressures correlate nicely with a particular set of theoretical predictions. This might be significant in that you could optimize for superconductivity by tuning the aggregate electromagnetic characteristics of a material rather than requiring hard-to-achieve structural uniformity at the molecular level.
  - selimthegrim 11y ago
    No, they're not subatomic. Charge density waves mean that there is a periodic modulation of charge (for a little more background, see the Quora answers here: http://www.quora.com/What-are-the-significances-of-charge-density-waves-CDW-and-spin-density-waves-SDW-in-condensed-matter-physics http://www.quora.com/What-are-the-significances-of-charge-de... and this pdf: http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes_2013/magnetism.pdf http://www.wien2k.at/reg_user/textbooks/WIEN2k_lecture-notes... ) What they are saying is that itinerant electrons (those not localized in a given orbital, but which occupy bands throughout the metallic system and hop, in contrast to an standard insulating magnet) have the instability within themselves, the lattice does not necessarily need to give them a push (this is called "dynamically generated"). In my answer I go into a bit of detail about the heretofore standard role of the lattice as well as the applications to superconductivity. What this paper is saying is that the Peierls distortion (cf. answers cited or Wikipedia) in these systems is either paralleling or a consequence of the electronic instability. The bit about following the Q wave vector has to do with the discussion of "nesting" in the answers (that is, how well does the momentum of the electrons couple with that of the phonons/ionic lattice vibrations at a certain periodicity and do they steal energy away from the lattice leading to an overall lower state (and is this the _primary_ factor in that lowering, a conclusion this paper would seem to militate against)" A good reference on this is the book by Assa Auerbach "Interacting Electrons and Quantum Magnetism"