Weekly Papers on Quantum Foundations (4)

This is a list of this week’s papers on quantum foundations published in various journals or uploaded to preprint servers such as arxiv.org and PhilSci Archive.

Finding the World in the Wave Function: Some Strategies for Solving the Macro-Object Problem

PhilSci-Archive: No conditions. Results ordered -Date Deposited.

on 2016-1-22 8:31pm GMT

Ney, Alyssa (2016) Finding the World in the Wave Function: Some Strategies for Solving the Macro-Object Problem. UNSPECIFIED.

Quantum self-gravitating collapsing matter in a quantum geometry. (arXiv:1601.05688v1 [gr-qc])

gr-qc updates on arXiv.org

on 2016-1-22 3:07am GMT

Authors: Miguel CampigliaRodolfo GambiniJavier OlmedoJorge Pullin

The problem of how space-time responds to gravitating quantum matter in full quantum gravity has been one of the main questions that any program of quantization of gravity should address. Here we analyze this issue by considering the quantization of a collapsing null shell coupled to spherically symmetric loop quantum gravity. We show that the constraint algebra of canonical gravity is Abelian both classically and when quantized using loop quantum gravity techniques. The Hamiltonian constraint is well defined and suitable Dirac observables characterizing the problem were identified at the quantum level. We can write the metric as a parameterized Dirac observable at the quantum level and study the physics of the collapsing shell and black hole formation. We show how the singularity inside the black hole is eliminated by loop quantum gravity and how the shell can traverse it. The construction is compatible with a scenario in which the shell tunnels into a baby universe inside the black hole or one in which it could emerge through a white hole.

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A top-down versus a bottom-up hidden-variables description of the Stern-Gerlach experiment. (arXiv:1601.05555v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-1-22 3:07am GMT

Authors: M. ArsenijevicJ. Jeknic-DugicM. Dugic

We employ the Stern-Gerlach experiment to highlight the basics of a minimalist, non-interpretational top-down approach to quantum foundations. Certain benefits of the here highlighted “quantum structural studies” are detected and discussed. While the top-down approach can be described without making any reference to the fundamental structure of a closed system, the hidden variables theory ?a la Bohm proves to be more subtle than it is typically regarded.

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Using quantum theory to reduce the complexity of input-output processes. (arXiv:1601.05420v1 [quant-ph])

quant-ph updates on arXiv.org

on 2016-1-22 3:07am GMT

Authors: Jayne ThompsonAndrew J. P. GarnerVlatko VedralMile Gu

All natural things process and transform information. They receive environmental information as input, and transform it into appropriate output responses. Much of science is dedicated to building models of such systems — algorithmic abstractions of their input-output behavior that allow us to simulate how such systems can behave in the future, conditioned on what has transpired in the past. Here, we show that classical models cannot avoid inefficiency — storing past information that is unnecessary for correct future simulation. We construct quantum models that mitigate this waste, whenever it is physically possible to do so. This suggests that the complexity of general input-output processes depends fundamentally on what sort of information theory we use to describe them.

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Measuring the quantum state of a single system with minimum state disturbance

PRA: Fundamental concepts

on 2016-1-21 3:00pm GMT

Author(s): Maximilian Schlosshauer

Conventionally, unknown quantum states are characterized using quantum-state tomography based on strong or weak measurements carried out on an ensemble of identically prepared systems. By contrast, the use of protective measurements offers the possibility of determining quantum states from a series …

[Phys. Rev. A 93, 012115] Published Thu Jan 21, 2016

Quantum asymmetry between time and space

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences current issue

on 2016-1-20 9:09am GMT

An asymmetry exists between time and space in the sense that physical systems inevitably evolve over time, whereas there is no corresponding ubiquitous translation over space. The asymmetry, which is presumed to be elemental, is represented by equations of motion and conservation laws that operate differently over time and space. If, however, the asymmetry was found to be due to deeper causes, this conventional view of time evolution would need reworking. Here we show, using a sum-over-paths formalism, that a violation of time reversal (T) symmetry might be such a cause. If T symmetry is obeyed, then the formalism treats time and space symmetrically such that states of matter are localized both in space and in time. In this case, equations of motion and conservation laws are undefined or inapplicable. However, if T symmetry is violated, then the same sum over paths formalism yields states that are localized in space and distributed without bound over time, creating an asymmetry between time and space. Moreover, the states satisfy an equation of motion (the Schrödinger equation) and conservation laws apply. This suggests that the time–space asymmetry is not elemental as currently presumed, and that T violation may have a deep connection with time evolution.

 

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