Abstracts for January 2016

  • $, which suppress off-diagonal components of the reduced density matrix, leaving a diagonal mixture of different classical configurations. Gravitational nonlinearities thus provide a minimal mechanism for generating classical stochastic perturbations from inflation. We identify the time when decoherence occurs, which is delayed after horizon crossing due to the weak coupling, and find that Hubble-scale modes act as the decohering environment. We also comment on the observational relevance of decoherence and its relation to the squeezing of the quantum state.’]
  • Right now I am wondering as to whether this can be connected to Crooks fluctuation theorem. (The Jarzynski equality is a special case of Crooks, and the second law is a special case of Jarzynski.) It also makes me want to spend more time reading Fleming’s imposing thesis, which is essentially a textbook on open quantum systems.

  • Look at how amazing this nested mirror is from Fig 1:

    That’s a real optical photograph! And they think that they will cool it to the ground state in the future.

  • H/t John Preskill, who advises you to take this seriously despite the many problems with previous attempts at finding quantum computation in the brain. See, e.g., Tegmark’s “The importance of quantum decoherence in brain processes”.

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Abstracts for October-November 2015

  • (H/t Sabine.) The contraction has been happening for quite some time:

    maximum c.o.m. energy has drastically slowed down since the early 1990’s and the lepton colliders even went backwards in energy to study rare processes…Moreover, the number of the colliding beam facilities in operation has dropped from 9 two decades ago to 5 now…

  • Possibly relevant to set selection problem or, more specifically, what are the quasiclassical degrees of freedom?

    This is one of the rare papersThe first place I can remember reading this distinction coming up clearly is the dispute over Zurek and Paz’s Hyperion example.a   where I’ve seen someone clearly point out these two conceptually distinct but tightly related explanation for classicality:

    In our everyday life, to experience macrorealism it is usually sufficient to employ a certain type of decoherence (where the system is isolated [4] and only at the times of measurement the environment
    makes a premeasurement on the apparatus [5]) or the restriction of coarse-grained measurements [6–9].

    I don’t think these explanations are actually in tension, in the sense that the more one applies the less it is necessary, to understand the emergence of classicality, to appeal to the other. More precisely, I think these are currently both “underspecified” explanations, and that a complete precise understanding will be expressible in either language by making certain terms in those languages more exact.

    One can talk about decoherence of the system by an environment, but then one needs to answer: What are systems? What are the environments? Alternatively, one can talk about certain preferred variables that can only be followed in a coarse-grained manner, but then one needs to answer: What are the variables?

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Abstracts for September 2015

I’m trying out a new type of post: a selection of abstracts I thought were particularly interesting this month (though not necessarily released this month). Some papers I’ll have read in detail, some not. I would be particularly interested in hearing commentary on them.

  • This papers has some intuition for how to think about symplectic geometry, which surprisingly still isn’t understood in a transparent intuitive way.

  • Proof-of-concept inflationary model producing natural Bell experiments (in the CMB?), which would testify to the quantum origins of primordial fluctuations. First time I’ve ever felt the inclination to learn about multi-field inflationary models.

  • Previously announced, but included here for completeness. Also see blog post by Scott Aaronson. I’m told that several experimental groups are very close to this, which is probably why this group announced ASAP rather than embargoing the preprint before it appears in Nature. Expect to see several new loophole-free Bell experiments using different systems (photons, electrons, etc.) from other group announced in the coming year or two.

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