# Weekly Papers on Quantum Foundations (20)

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.

Spacetime-free Approach to Quantum Theory and Effective Spacetime Structure. (arXiv:1605.03942v1 [gr-qc])

on 2016-5-14 9:34am GMT

Authors: Matti Raasakka

Motivated by hints of the effective emergent nature of spacetime structure, we develop a spacetime-free framework for quantum theory. We find that quantum states on an extended observable algebra, the free algebra generated by the observables, may give rise to effective spacetime structures. Accordingly, perturbations of the quantum state (e.g., excitations of the vacuum) lead to perturbations of the induced effective spacetime geometry. We initiate the study of these perturbations, and their relation to gravitational phenomena.

Quasi-matter bounce and inflation in the light of the CSL model. (arXiv:1605.03632v1 [gr-qc])

on 2016-5-14 9:34am GMT

The Continuous Spontaneous Localization (CSL) model has been proposed as a possible solution to the quantum measurement problem by modifying the Schr\”{o}dinger equation. In this work, we apply the CSL model to two cosmological models of the early Universe: the matter bounce scenario and slow roll inflation. In particular, we focus on the generation of the classical primordial inhomogeneities and anisotropies that arise from the dynamical evolution, provided by the CSL mechanism, of the quantum state associated to the quantum fields. In each case, we obtained a prediction for the shape and the parameters characterizing the primordial spectra (scalar and tensor), i.e. the amplitude, the spectral index and the tensor-to-scalar ratio. We found that there exist CSL parameter values, allowed by other non-cosmological experiments, for which our predictions for the angular power spectrum of the CMB temperature anisotropy are consistent with the best fit canonical model to the latest data released by the Planck Collaboration.

An anomaly in space and time and the origin of dynamics

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

on 2016-5-13 4:52pm GMT

Vaccaro, Joan A (2016) An anomaly in space and time and the origin of dynamics. [Preprint]

Discriminating the effects of collapse models from environmental diffusion with levitated nanospheres

Recent Articles in Phys. Rev. A

on 2016-5-13 2:00pm GMT

Author(s): Jie Li, Stefano Zippilli, Jing Zhang, and David Vitali

Collapse models postulate the existence of intrinsic noise which modifies quantum mechanics and is responsible for the emergence of macroscopic classicality. Assessing the validity of these models is extremely challenging because it is nontrivial to discriminate unambiguously their presence in exper…

[Phys. Rev. A 93, 050102(R)] Published Fri May 13, 2016

Discriminating the effects of collapse models from environmental diffusion with levitated nanospheres

PRA: Fundamental concepts

on 2016-5-13 2:00pm GMT

Author(s): Jie Li, Stefano Zippilli, Jing Zhang, and David Vitali

Collapse models postulate the existence of intrinsic noise which modifies quantum mechanics and is responsible for the emergence of macroscopic classicality. Assessing the validity of these models is extremely challenging because it is nontrivial to discriminate unambiguously their presence in exper…

[Phys. Rev. A 93, 050102(R)] Published Fri May 13, 2016

Chaos and Stochastic Models in Physics: Ontic and Epistemic Aspects

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

on 2016-5-11 5:26am GMT

Caprara, Sergio and Vulpiani, Angelo (2016) Chaos and Stochastic Models in Physics: Ontic and Epistemic Aspects. [Published Article]

Proposed Macroscopic Test of the Physical Relevance of Bell’s Theorem

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

on 2016-5-11 5:18am GMT

Christian, Joy (2016) Proposed Macroscopic Test of the Physical Relevance of Bell’s Theorem. [Preprint]

What is Physics: The individual and the universal, and seeing past the noise. (arXiv:1605.03106v1 [physics.hist-ph])

on 2016-5-11 2:00am GMT

Authors: A. R. P. Rau

Along with weaving together observations, experiments, and theoretical constructs into a coherent mesh of understanding of the world around us, physics over its past five centuries has continuously refined the base concepts on which the whole framework is built. In quantum physics, first in non-relativistic mechanics and later in quantum field theories, even familiar concepts of position, momentum, wave or particle, are derived constructs from the classical limit in which we live but not intrinsic to the underlying physics. Most crucially, the very idea of the individual, whether an object or an event, distinguished only in a mere label of identity from others identical to it in all the physics, exists only as an approximation, not an element of underlying reality. Failure to recognize this and seeking alternative explanations in many worlds or multiverses leads only to incoherent logic and incorrect physics.

As an example, in a physical system such as an atom in a particular state, physics deals with the universal system of all such atoms but makes no meaningful prediction of the position of an electron or the time of decay of any specific atom. Those are incidental, entirely random among all possible positions and times, even while physics makes very precise predictions for the distribution of the outcomes in measurements on atoms in that state. Physics deals with the universal, not the individual.

Space-time symmetric extension of non-relativistic quantum mechanics. (arXiv:1605.03121v1 [quant-ph])

on 2016-5-11 2:00am GMT

Authors: Eduardo O. DiasFernando Parisio

In quantum theory we speak of the probability to find a particle between positions $x$ and $x+dx$ at the instant $t$, although we have no capacity of exactly predicting when the detection occurs. In this work, first we present an extended non-relativistic quantum formalism where space and time play equivalent roles. It leads to the probability of finding a particle between $x$ and $x+dx$ during [$t$,$t+dt$]. Then, we find a Schr\”odinger-like equation for a “mirror” wave function $\phi(t,x)$ associated with the probability to measure the system between $t$ and $t+dt$, given that detection occurs at $x$. In this framework, it is shown that energy measurements of a stationary state display a non-zero dispersion. We show that a central result on arrival time, obtained through approaches that resort to {\it ad hoc} assumptions, is a natural, built-in part of the formalism presented here. Finally, we verify that energy-time uncertainty arises from first principles.

Quantum weak values and logic, an uneasy couple. (arXiv:1605.03023v1 [quant-ph])

on 2016-5-11 2:00am GMT

Authors: B. E. Y. Svensson

Quantum mechanical weak values of projection operators have been used to answer which-way questions, e.g., to trace which arms in a multiple Mach-Zehnder setup a particle may have traversed from a given initial to a prescribed final state. I show that this procedure might lead to logical inconsistencies in the sense that different methods used to answer composite questions, like Has the particle traversed the way X or the way Y?, may result in different answers depending on which methods is used to find the answer. I illustrate by considering some examples: the quantum pigeonhole framework of Aharonov et al, the three-box problem, and the Hardys paradox.Without really presenting any new results, but more to prepare the ground for my main conclusion on the incompatibility in certain cases of weak values and logic, I also study the corresponding situation for strong/projective measurements. Here, no logical inconsistencies occur provided, as I stress, one is always careful in specifying to which ensemble or sample space one refers. My results cast doubts on the utility of weak values in treating foundational issues in quantum mechanics.

A physical interpretation of Lewis’ discrepancy between personal and external time in time travels

Latest Results for Synthese

on 2016-5-11 12:00am GMT

Abstract

This paper deals with those time travels mostly considered by physics, namely those in the form of the so-called closed timelike curves. Some authoritative scholars have raised doubts about the status of these journeys as proper time travels. By using David Lewis’ famous definition of time travels proposed in 1976, we show that this proper status may actually be recovered, at least in some cosmological contexts containing spacetime regions, such as those concerning black holes described by the Kerr–Newman metric, that allow the formation of local closed curves. But, the mathematical incompatibility between ordinary black hole solutions to Einstein field equations and the cosmological solutions induces us to take into consideration the more general issue pertaining to the slippery interplay between models related to local and global aspects of the world, highlighting, in particular, the different notions of time that these domains inevitably imply. This leads us to think that time is not a univocal entity of the world, but is a scale-related characteristic which claims the adoption, when investigating its ontological status, of a sort of regional approach. We also briefly dwell upon the most appropriate form of realism that such a kind of dispute between local and global models may involve.

Symmetry Reduced Loop Quantum Gravity: A Bird’s Eye View. (arXiv:1605.02648v1 [gr-qc])

on 2016-5-10 2:09am GMT

Authors: Abhay Ashtekar

This is a brief overview of the current status of symmetry reduced models in Loop Quantum Gravity. The goal is to provide an introduction to other more specialized and detailed reviews that follow. Since most of this work is motivated by the physics of the very early universe, I will focus primarily on Loop Quantum Cosmology and discuss quantum aspects of black holes only briefly.

“Counterfactual” quantum protocols. (arXiv:1605.02181v1 [quant-ph])

on 2016-5-10 2:09am GMT

Authors: Lev Vaidman

The counterfactuality of recently proposed protocols is analyzed. A definition of counterfactuality’ is offered and it is argued that an interaction-free measurement of the presence of an opaque object can be named counterfactual’, while proposed “counterfactual” measurements of the absence of such objects are not counterfactual. The quantum key distribution protocols which rely only on measurements of the presence of the object are counterfactual, but quantum direct communication protocols are not. Therefore, the name `counterfactual’ is not appropriate for recent “counterfactual” protocols which transfer quantum states by quantum direct communication.

On the Uncertainty Principle for Continuous Quantum Measurement. (arXiv:1605.02312v1 [quant-ph])

on 2016-5-10 2:09am GMT

Authors: Haixing Miao

We revisit the Heisenberg uncertainty principle for continuous quantum measurement with the detector describable by linear response. When the detector is at the quantum limit with minimum uncertainty, the fluctuation and response of a single-input single-output detector are shown to be related via two equalities. We illustrate the result by applying it to an optomechanical device–a typical continuous measurement setup.

Bounds on collapse models from cold-atom experiments. (arXiv:1605.01891v1 [quant-ph])

on 2016-5-09 1:09am GMT

The spontaneous localization mechanism of collapse models induces a Brownian motion in all physical systems. This effect is very weak, but experimental progress in creating ultracold atomic systems can be used to detect it. In this paper, we considered a recent experiment [1], where an atomic ensemble was cooled down to picokelvins. Any Brownian motion induces an extra increase of the position variance of the gas. We study this effect by solving the dynamical equations for the Continuous Spontaneous Localizations (CSL) model, as well as for its non-Markovian and dissipative extensions. The resulting bounds, with a 95% of confidence level, are beaten only by measurements of spontaneous X-ray emission and by experiments with cantilever (in the latter case, only for rC > 10^(-7) m, where rC is one of the two collapse parameters of the CSL model). We show that, contrary to the bounds given by X-ray measurements, non-Markovian effects do not change the bounds, for any reasonable choice of a frequency cutoff in the spectrum of the collapse noise. Therefore the bounds here considered are more robust. We also show that dissipative effects are unimportant for a large spectrum of temperatures of the noise, while for low temperatures the excluded region in the parameter space is the more reduced, the lower the temperature.

Detecting continuous spontaneous localisation with charged bodies in a Paul trap. (arXiv:1605.01881v1 [quant-ph])

on 2016-5-09 1:09am GMT

Continuous spontaneous localisation (CSL) is a model that captures the effects of a class of extensions to quantum theory which are expected to result from quantum gravity, and is such that wavefunction collapse is a physical process. The rate of such a process could be very much lower than the upper bounds set by searches to date, and yet still modify greatly the interpretation of quantum mechanics and solve the quantum measurement problem. Consequently experiments are sought to explore this. We describe an experiment that has the potential to extend sensitivity to CSL by many orders of magnitude. The method is to detect heating of the motion of charged macroscopic objects confined in a Paul trap. We discuss the detection and the chief noise sources. We find that CSL with standard parameters could be observed using a vibration-isolated ion trap of size 1 cm at ultra-low pressure, with optical interferometric detection.

Constructibility of the Universal Wave Function

Latest Results for Foundations of Physics

on 2016-5-09 12:00am GMT

Abstract

This paper focuses on a constructive treatment of the mathematical formalism of quantum theory and a possible role of constructivist philosophy in resolving the foundational problems of quantum mechanics, particularly, the controversy over the meaning of the wave function of the universe. As it is demonstrated in the paper, unless the number of the universe’s degrees of freedom is fundamentally upper bounded (owing to some unknown physical laws) or hypercomputation is physically realizable, the universal wave function is a non-constructive entity in the sense of constructive recursive mathematics. This means that even if such a function might exist, basic mathematical operations on it would be undefinable and subsequently the only content one would be able to deduce from this function would be pure symbolical.

Review of Mathias Frisch’s Causal Reasoning in Physics

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

on 2016-5-08 7:00am GMT

Farr, Matt (2016) Review of Mathias Frisch’s Causal Reasoning in Physics. [Preprint]