# Weekly Papers on Quantum Foundations (40)

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.

No-Hypersignaling as a Physical Principle. (arXiv:1609.09237v1 [quant-ph])

on 2016-10-01 3:20am GMT

A paramount topic in quantum foundations, rooted in the study of the EPR paradox and Bell inequalities, is that of characterizing quantum theory in terms of the space-like correlations it allows. Here we show that to focus only on space-like correlations is not enough: we explicitly construct a toy model theory that, though being perfectly compatible with classical and quantum theories at the level of space-like correlations, displays an anomalous behavior in its time-like correlations. We call this anomaly, quantified in terms of a specific communication game, the “hypersignaling” phenomena. We hence conclude that the “principle of quantumness,” if it exists, cannot be found in space-like correlations alone: nontrivial constraints need to be imposed also on time-like correlations, in order to exclude hypersignaling theories.

Quantum common causes and quantum causal models. (arXiv:1609.09487v1 [quant-ph])

on 2016-10-01 3:20am GMT

Reichenbach’s principle asserts that if two observed variables are found to be correlated, then there should be a causal explanation of these correlations. Furthermore, if the explanation is in terms of a common cause, then the conditional probability distribution over the variables given the complete common cause should factorize. The principle is generalized by the formalism of causal models, in which the causal relationships among variables constrain the form of their joint probability distribution. In the quantum case, however, the observed correlations in Bell experiments cannot be explained in the manner Reichenbach’s principle would seem to demand. Motivated by this, we introduce a quantum counterpart to the principle. We demonstrate that under the assumption that quantum dynamics is fundamentally unitary, if a quantum channel with input A and outputs B and C is compatible with A being a complete common cause of B and C, then it must factorize in a particular way. Finally, we show how to generalize our quantum version of Reichenbach’s principle to a formalism for quantum causal models, and provide examples of how the formalism works.

A Quantum Information Geometric Approach to Renormalization. (arXiv:1609.09440v1 [quant-ph])

on 2016-10-01 3:20am GMT

Authors: John B. DeBrota

This essay constitutes a review of the information geometric approach to renormalization developed in the recent works of B\’eny and Osborne as well as a detailed work-through of some of their contents. A noncommutative generalization of information geometry allows one to treat quantum state distinguishability in geometric terms with an intuitive empirical interpretation, allowing for an information theoretic prescription of renormalization which incorporates both the condensed matter and quantum field theoretic approaches.

A Bilocal Model for the Relativistic Spinning Particle. (arXiv:1609.09110v1 [hep-th])

on 2016-10-01 3:18am GMT

Authors: Trevor RempelLaurent Freidel

In this work we show that a relativistic spinning particle can be described at the classical and the quantum level as being composed of two physical constituents which are entangled and separated by a fixed distance. This bilocal model for spinning particles allows for a natural description of particle interactions as a local interaction at each of the constituents. This form of the interaction vertex provides a resolution to a long standing issue on the nature of relativistic interactions for spinning objects in the context of the worldline formalism. It also potentially brings a dynamical explanation for why massive fundamental objects are naturally of lowest spin. We analyze first a non-relativistic system where spin is modeled as an entangled state of two particles with the entanglement encoded into a set of constraints. It is shown that these constraints can be made relativistic and that the resulting description is isomorphic to the usual description of the phase space of massive relativistic particles with the restriction that the quantum spin has to be an integer.

Relativistic quantum clocks. (arXiv:1609.09426v1 [quant-ph])

on 2016-9-30 9:01am GMT

Authors: Maximilian P. E. LockIvette Fuentes

The conflict between quantum theory and the theory of relativity is exemplified in their treatment of time. We examine the ways in which their conceptions differ, and describe a semiclassical clock model combining elements of both theories. The results obtained with this clock model in flat spacetime are reviewed, and the problem of generalizing the model to curved spacetime is discussed, before briefly describing an experimental setup which could be used to test of the model. Taking an operationalist view, where time is that which is measured by a clock, we discuss the conclusions that can be drawn from these results, and what clues they contain for a full quantum relativistic theory of time.

The Stern-Gerlach Experiment Revisited. (arXiv:1609.09311v1 [physics.hist-ph])

on 2016-9-30 9:01am GMT

The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment of quantum physics providing evidence for several fundamental properties of quantum systems. Based on today’s knowledge we illustrate the different benchmark results of the SGE for the development of modern quantum physics and chemistry.

The SGE provided the first direct experimental evidence for angular momentum quantization in the quantum world and thus also for the existence of directional quantization of all angular momenta in the process of measurement. It measured for the first time a ground state property of an atom, it produced for the first time a spin-polarized’ atomic beam, it almost revealed the electron spin. The SGE was the first fully successful molecular beam experiment with high momentum-resolution by beam measurements in vacuum. This technique provided a new kinematic microscope with which inner atomic or nuclear properties could be investigated.

The original SGE is described together with early attempts by Einstein, Ehrenfest, Heisenberg, and others to understand directional quantization in the SGE. Heisenberg’s and Einstein’s proposals of an improved multi-stage SGE are presented. The first realization of these proposals by Stern, Phipps, Frisch and Segr\e is described. The set-up suggested by Einstein can be considered an anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which the directional quantization process and possible interference effects of the two different spin states are investigated.

In full agreement with the results of the new quantum theory directional quantization appears as a general and universal feature of quantum measurements. One experimental example for such directional quantization in scattering processes is shown. Last not least, the early history of the `almost’ discovery of the electron spin in the SGE is revisited.

The metaphysics of D-CTCs: On the underlying assumptions of Deutsch׳s quantum solution to the paradoxes of time travel

ScienceDirect Publication: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics

on 2016-9-30 2:10am GMT

Publication date: Available online 28 September 2016
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Lucas Dunlap
I argue that Deutsch׳s model for the behavior of systems traveling around closed timelike curves (CTCs) relies implicitly on a substantive metaphysical assumption. Deutsch is employing a version of quantum theory with a significantly supplemented ontology of parallel existent worlds, which differ in kind from the many worlds of the Everett interpretation. Standard Everett does not support the existence of multiple identical copies of the world, which the D-CTC model requires. This has been obscured because he often refers to the branching structure of Everett as a “multiverse”, and describes quantum interference by reference to parallel interacting definite worlds. But he admits that this is only an approximation to Everett. The D-CTC model, however, relies crucially on the existence of a multiverse of parallel interacting worlds. Since his model is supplemented by structures that go significantly beyond quantum theory, and play an ineliminable role in its predictions and explanations, it does not represent a quantum solution to the paradoxes of time travel.

Lectures on Gravity and Entanglement. (arXiv:1609.00026v1 [hep-th] CROSS LISTED)

on 2016-9-29 12:44am GMT

Authors: Mark Van Raamsdonk

The AdS/CFT correspondence provides quantum theories of gravity in which spacetime and gravitational physics emerge from ordinary non-gravitational quantum systems with many degrees of freedom. Recent work in this context has uncovered fascinating connections between quantum information theory and quantum gravity, suggesting that spacetime geometry is directly related to the entanglement structure of the underlying quantum mechanical degrees of freedom and that aspects of spacetime dynamics (gravitation) can be understood from basic quantum information theoretic constraints. In these notes, we provide an elementary introduction to these developments, suitable for readers with some background in general relativity and quantum field theory. The notes are based on lectures given at the CERN Spring School 2014, the Jerusalem Winter School 2014, the TASI Summer School 2015, and the Trieste Spring School 2015.

Nancy Cartwright and the Logic of Quantum Mechanics. (arXiv:1606.00351v2 [physics.hist-ph] UPDATED)

on 2016-9-29 12:44am GMT

Authors: Pascal Lederer

This paper deals with Nancy Cartwright’s views on the measurement problem in Quantum Mechanics, as exposed in her book {\it{How the Laws of Physics Lie}}. She does not accept the logic of Quantum Mechanics. It is argued that her proposals, which are at variance with many facts results and epistemics of Quantum Mechanics are the result of her choice of classical logic, which leads her to propose the transition rate as the fundamental object of Quantum Mechanics. I argue that this is incorrect. The positions which Nancy Cartwright defends on the reduction of the wave packet do not address the fundamental issue, i.e. the duality of a world where quantum and classical objects coexist and interact. I suggest that the main problem with Nancy Cartwright’s positions is her difficulty in accepting that the contradiction at the basis of Quantum Mechanics, i.e. the simultaneous corpuscular and wave-like nature of quantum objects, is a fact of nature. Recent experiments, described in this paper, shed a new light on the foundations of Quantum Mechanics and on the topic of this paper. The limits of the no-contradiction principle are discussed; modern dialectical materialism is argued to offer a useful framework for the interplay between knowledge and reality.

How to justify Born’s rule using the pilot wave theory of de Broglie?. (arXiv:1609.08992v1 [quant-ph])

on 2016-9-29 12:44am GMT

Authors: A. Drezet

In this article we discuss few new derivations of the so called Born’s rule for quantum probability in the context of the pilot wave theory proposed by de Broglie in 1927.

Reply to Ben-Israel and Vaidman, Comment on Non-representative Quantum Mechanical Weak values. (arXiv:1609.08977v1 [quant-ph])

on 2016-9-29 12:44am GMT

Authors: Svensson B E Y

Ben-Israel and Vaidman (arXiv:1608.07185) raise objections to my arguments that there are cases where a quantum mechanical weak value can be said not to represent the system to which it pertains. They are right in pointing out that some of my conclusions are too general. However, there are still cases where my conclusions withstand to their scrutiny.

### One Response

1. jacksarfatti at |

https://arxiv.org/abs/1609.09237

No-Hypersignaling as a Physical Principle
(Submitted on 29 Sep 2016)

Quantum Physics

A paramount topic in quantum foundations, rooted in the study of the EPR paradox and Bell inequalities, is that of characterizing quantum theory in terms of the space-like correlations it allows. Here we show that to focus only on space-like correlations is not enough: we explicitly construct a toy model theory that, though being perfectly compatible with classical and quantum theories at the level of space-like correlations, displays an anomalous behavior in its time-like correlations. We call this anomaly, quantified in terms of a specific communication game, the “hypersignaling” phenomena. We hence conclude that the “principle of quantumness,” if it exists, cannot be found in space-like correlations alone: nontrivial constraints need to be imposed also on time-like correlations, in order to exclude hypersignaling theories.
Submission history

From: Michele Dall’Arno [view email]
[v1] Thu, 29 Sep 2016 07:42:03 GMT (839kb)

This paper asks the wrong question.

1) No signaling is not fundamental. It is true for quantum theory, but it is not true for post-quantum theory. No-signaling is a consequence
of no direct back-reaction of beables on their pilot waves in the sense of Bohm 1952 updated by Sutherland 2015. Quantum theory is
a limiting case of post-quantum theory in the same way that special relativity is a limiting case of general relativity.

2) As shown by Costa de Beauregard, Huw Price, Ken Wharton, Rod Sutherland … spacelike correlations are an illusion. What is
really going on is the “zig-zag” i.e. locally real retrocausal influences that are compatible with Einstein’s relativity. What Bell’s 1964 theorem
really proves is that quantum theory (without signaling) requires that future strong measurements act backwards in time on the entangled
state’s past creation. That is, the “spooky” aspects of quantum theory are most naturally and simply explained as local retrocausal
influences not by faster-than-light “tachyonic” effects of any kind. In post-quantum theory, these retrocausal influences can be harnessed
and controlled for locally decodable messaging without needing a classical retarded signal key to unlock the message encoded in
the pattern of quantum entanglement. As shown by Antony Valentini (2002) this enables the hacking of seemingly secure quantum cryptographic
systems at least in principle if not yet in practice. The post-quantum version of the black hole information paradox seems to validate
Stephen Hawking’s earlier position and invalidate the premise’s of Leonard Susskind’s premise that quantum information is never created
or destroyed.