# Weekly Papers on Quantum Foundations (25)

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.

Process-theoretic characterisation of the Hermitian adjoint. (arXiv:1606.05086v1 [quant-ph])

on 2016-6-17 12:26pm GMT

Authors: John SelbyBob Coecke

We show that the physical principle “the adjoint associates to each state a `test’ for that state” fully characterises the Hermitian adjoint for pure quantum theory, therefore providing the adjoint with operational meaning beyond its standard mathematical definition. Also, we show that for general process theories, which all admit a diagrammatic representation, this physical principle induces a reflection operation.

Quantum mechanics in terms of realism

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

on 2016-6-17 5:49am GMT

Jabs, Arthur (2016) Quantum mechanics in terms of realism. [Published Article or Volume]

[In Depth] LIGO detects another black hole crash

Science: Current Issue

on 2016-6-17 12:00am GMT

The biggest discovery in science this year—the observation of ripples in space-time called gravitational waves—was no fluke. For a second time, physicists working with the two massive detectors in the Laser Interferometer Gravitational-Wave Observatory (LIGO) have detected a pulse of such waves, the LIGO team reported on 15 June at a meeting of the American Astronomical Society in San Diego, California. Once again the waves emanated from the merger of two black holes, the ultraintense gravitational fields left behind when massive stars collapse into infinitesimal points. The new observation suggests that if LIGO’s detectors reach their design sensitivity—which physicists hope to achieve by 2019—the observatory will spot dozens or even hundreds of the otherwise undetectable events each year, ushering in a new era of gravitational-wave astronomy. Author: Adrian Cho

The time-dependent Schrodinger equation for a closed quantum system. (arXiv:1606.04759v1 [quant-ph])

on 2016-6-16 3:32am GMT

Ever since Schrodinger, the time-dependent Schrodinger equation has been regarded as the fundamental physical law of the unitary-only quantum theory. However, while the origin of time for non-conservative systems can be traced back to the environmental influence, this procedure is inapplicable for the closed (conservative) quantum systems. Hence the question of the origin of time for closed systems. In addressing this issue, in order to avoid circularity of the standard universal (global) time as well as assumptions that could be additional to the standard postulates of quantum theory, we stick to the so-called quantum-mechanical local time. The problems that inevitably appear in such minimalist rejection of the standard role of time in physics are solved with mathematical rigor while leading to the emergent time for every, at least approximately, closed (conservative) system as well as to establishing the time-dependent Schrodinger law as the fundamental law of the unitary non-relativistic as well as relativistic-field quantum theory.

Double-slit experiment in momentum space. (arXiv:1606.04732v1 [quant-ph])

on 2016-6-16 3:32am GMT

Authors: I. P. IvanovD. SeiptA. SurzhykovS. Fritzsche

Young’s classic double-slit experiment demonstrates the reality of interference when waves and particles travel simultaneously along two different spatial paths. Here, we propose a double-slit experiment in momentum space. We show that elastic scattering of vortex electrons proceeds via two paths in momentum space, which are well localized and well separated from each other. For such vortex beams, the (plane-wave) amplitudes along the two paths acquire adjustable phase shifts and produce interference fringes in the final angular distribution. We argue that this experiment can be realized with the present day technology. We show that it gives experimental access to the Coulomb phase, a quantity which plays an important role in all charged particle scattering but which usual scattering experiments are insensitive to.

Experimental bounds on collapse models from gravitational wave detectors. (arXiv:1606.04581v1 [quant-ph])

on 2016-6-16 3:32am GMT

Authors: M. CarlessoA. BassiP. FalferiA. Vinante

Wave function collapse models postulate a fundamental breakdown of the quantum superposition principle at the macroscale. Therefore, experimental tests of collapse models are also fundamental tests of quantum mechanics. Therefore, experimental tests of collapse models can be regarded as fundamental tests of the quantum superposition principle. Here, we compute the upper bounds on the collapse parameters, which can be inferred by the gravitational wave detectors AURIGA, LIGO and LISA Pathfinder. We consider the most widely used collapse model, the Continuous Spontaneous Localization (CSL) model. We show that these experiments exclude a huge portion of the CSL parameter space, the strongest bound being set by the recently launched space mission LISA Pathfinder.

Spying on photons with photons: quantum interference and information. (arXiv:1606.04729v1 [quant-ph])

on 2016-6-16 3:32am GMT

Authors: Stefan Ataman

The quest to have both which-path knowledge and interference fringes in a double-slit experiment dates back to the inception of quantum mechanics (QM) and to the famous Einstein-Bohr debates. In this paper we propose and discuss an experiment able to spy on one photon’s path with another photon. We modify the quantum state inside the interferometer as opposed to the traditional physical modification of the “wave-like” or “particle-like” experimental setup. We are able to show that it is the ability to harvest or not which-path information that finally limits the visibility of the interference pattern and not the “wave-like” or “particle-like” experimental setups. Remarkably, a full “particle-like” experimental setup is able to show interference fringes with 100 % visibility if the quantum state is carefully engineered.

Quantum-coherent mixtures of causal relations. (arXiv:1606.04523v1 [quant-ph])

on 2016-6-15 7:56am GMT

Understanding the causal influences that hold among the parts of a system is critical both to explaining that system’s natural behaviour and to controlling it through targeted interventions. In a quantum world, understanding causal relations is equally important, but the set of possibilities is far richer. The two basic ways in which a pair of time-ordered quantum systems may be causally related are by a cause-effect mechanism or by a common cause acting on both. Here, we show that it is possible to have a coherent mixture of these two possibilities. We realize such a nonclassical causal relation in a quantum optics experiment and derive a set of criteria for witnessing the coherence based on a quantum version of Berkson’s paradox. The interplay of causality and quantum theory lies at the heart of challenging foundational puzzles, such as Bell’s theorem and the search for quantum gravity, but could also provide a resource for novel quantum technologies.

GHZ states and PR boxes in the classical limit. (arXiv:1606.04274v1 [quant-ph])

on 2016-6-15 7:56am GMT

Authors: Daniel RohrlichGuy Hetzroni

A recent paper [1] argues that bipartite “PR-box” correlations, though designed to respect relativistic causality, in fact violate relativistic causality in the classical limit. As a test of Ref. [1], we consider GHZ correlations as a tripartite version of PR-box correlations, and ask whether the arguments of Ref. [1] extend to GHZ correlations. If they do – i.e. if they show that GHZ correlations violate relativistic causality in the classical limit – then Ref. [1] must be incorrect, since GHZ correlations are quantum correlations and respect relativistic causality. But the arguments fail. We also show that both PR-box correlations and GHZ correlations can be retrocausal, but the retrocausality of PR-box correlations leads to self-contradictory causal loops, while the retrocausality of GHZ correlations does not.

Unscrambling the Quantum Omelette of Epistemic and Ontic Contextuality: Classical Contexts and Quantum Reality

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

on 2016-6-14 11:40pm GMT

de Ronde, Christian (2016) Unscrambling the Quantum Omelette of Epistemic and Ontic Contextuality: Classical Contexts and Quantum Reality. [Preprint]

A conjecture concerning determinism, reduction, and measurement in quantum mechanics

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

on 2016-6-14 11:36pm GMT

Jabs, Arthur (2016) A conjecture concerning determinism, reduction, and measurement in quantum mechanics. [Published Article or Volume]

Scientific Realism and Primordial Cosmology

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

on 2016-6-14 11:32pm GMT

Azhar, Feraz and Butterfield, Jeremy (2016) Scientific Realism and Primordial Cosmology. [Preprint]

LISA pathfinder appreciably constrains collapse models. (arXiv:1606.03637v1 [quant-ph])

on 2016-6-14 9:25am GMT

LISA Pathfinder’s measurement of a relative acceleration noise between two free-falling test masses with a square root of the power spectral density of $5.2 \pm 0.1 \mbox{ fm s}^{-2}/\sqrt{\rm{Hz}}$ appreciably constrains collapse models. In particular, we bound the localization rate parameter, $\lambda_{\rm CSL}$, in the continuous spontaneous localization model (CSL) to be at most $\left( 2.96 \pm 0.12 \right) \times 10^{-8} \mbox{ s}^{-1}$. Moreover, we bound the regularization scale, $\sigma_{\rm DP}$, used in the Diosi-Penrose (DP) model to be at least $40.1 \pm 0.5 \mbox{ fm}$. These bounds significantly constrain the validity of these models. In particular: (i) a lower bound of $2.2 \times 10^{-8\pm2} \mbox{s}^{-1}$ for $\lambda_{\rm CSL}$ has been proposed in (although a lower bound of about $10^{-17} \mbox{s}^{-1}$ is sometimes used), in order for the collapse noise to be substantial enough to explain the phenomenology of quantum measurement, and (ii) 40 fm is larger than the size of any nucleus, while the regularization scale has been proposed to be the size of the nucleus.

Toward an Understanding of Parochial Observables

The British Journal for the Philosophy of Science – Advance Access

on 2016-6-13 5:54am GMT

Ruetsche ([2011]) claims that an abstract C*-algebra of observables will not contain all of the physically significant observables for a quantum system with infinitely many degrees of freedom. This would signal that in addition to the abstract algebra, one must use Hilbert space representations for some purposes. I argue to the contrary that there is a way to recover all of the physically significant observables by purely algebraic methods.

• 1 Introduction
• 2 Preliminaries
• 3 Three Extremist Interpretations
• 3.1 Algebraic imperialism
•  3.2 Hilbert space conservatism
• 3.3 Universalism
• 4 Parochial Observables
• 4.1 Parochial observables for the imperialist
• 4.2 Parochial observables for the universalist
• 5 Conclusion