Weekly Papers on Quantum Foundations (31)

Abstract

We argue that causal decision theory (CDT) is no worse off than evidential decision theory (EDT) in handling entanglement, regardless of one’s preferred interpretation of quantum mechanics. In recent works, Ahmed (Evidence, decision, and causality, Cambridge University Press, Cambridge, 2014) and Ahmed and Caulton (Synthese, 191(18): 4315–4352, 2014) have claimed the opposite; we argue that they are mistaken. Bell-type experiments are not instances of Newcomb problems, so CDT and EDT do not diverge in their recommendations. We highlight the fact that a Causal Decision Theorist should take all lawlike correlations into account, including potentially acausal entanglement correlations. This paper also provides a brief introduction to CDT with a motivating “small” Newcomb problem. The main point of our argument is that quantum theory does not provide grounds for favouring EDT over CDT.

Authors: Christoph Adami

Leggett and Garg derived inequalities that probe the boundaries of classical and quantum physics by putting limits on the properties that classical objects can have. Historically, it has been suggested that Leggett-Garg inequalities are easily violated by quantum systems undergoing sequences of strong measurements, casting doubt on whether quantum mechanics correctly describes macroscopic objects. Here I show that Leggett-Garg inequalities cannot be violated by any projective measurement. The perceived violation of the inequalities found previously can be traced back to an inappropriate assumption of non-invasive measurability. Surprisingly, weak projective measurements cannot violate the Leggett-Garg inequalities either because even though the quantum system itself is not fully projected via weak measurements, the measurement devices

Authors: Marco GenoveseMarco Gramegna

In this paper we make an extensive description of quantum non-locality, one of the most intriguing and fascinating facets of quantum mechanics. After a general presentation of several studies on this subject, we consider if quantum non-locality, and the friction it carries with special relativity, can eventually find a “solution” by considering higher dimensional spaces.

Authors: Christoph Adami

The Leggett-Garg inequalities probe the classical-quantum boundary by putting limits on the sum of pairwise correlation functions between classical measurement devices that consecutively measured the same quantum system. The apparent violation of these inequalities by standard quantum measurements has cast doubt on quantum mechanics’ ability to consistently describe classical objects. Recent work has concluded that these inequalities cannot be violated by either strong or weak projective measurements [1]. Here I consider an entropic version of the Leggett-Garg inequalities that are different from the standard inequalities yet similar in form, and can be defined without reference to any particular observable. I find that the entropic inequalities also cannot be be violated by strong quantum measurements. The entropic inequalities can be extended to describe weak quantum measurements, and I show that these weak entropic Leggett-Garg inequalities cannot be violated either even though the quantum system remains unprojected, because the inequalities describe the classical measurement devices, not the quantum system. I conclude that quantum mechanics adequately describes classical devices, and that we should be careful not to assume that the classical devices accurately describe the quantum system.

Authors: Benjamin RousselAlexandre Feller

Moving detectors in relativistic quantum field theories reveal the fundamental entangled structure of the vacuum which manifests, for instance, through its thermal character when probed by a uniformly accelerated detector. In this paper, we propose a general formalism inspired both from signal processing and correlation functions of quantum optics to analyze the response of point-like detectors following a generic, non-stationary trajectory. In this context, the Wigner representation of the first-order correlation of the quantum field is a natural time-frequency tool to understand single-detection events. This framework offers a synthetic perspective on the problem of detection in relativistic theory and allows us to analyze various non-stationary situations (adiabatic, periodic) and how excitations and superpositions are deformed by motion. It opens up interesting perspective on the issue of the definition of particles.

下午5:21 | gr-qc updates on arXiv.org

Authors: Raphael BoussoArvin Shahbazi-MoghaddamMarija Tomasevic

The classical Penrose inequality specifies a lower bound on the total mass in terms of the area of certain trapped surfaces. This fails at the semiclassical level. We conjecture a quantum Penrose inequality: the mass at spatial infinity is lower-bounded by a function of the generalized entropy of the lightsheet of any quantum marginally trapped surface. This is the first relation between quantum information in quantum gravity, and total energy.

Authors: Arun MathewMalay K. Nandy

Newtonian gravity predicts the existence of white dwarfs with masses far exceeding the Chandrasekhar limit when the equation of state of the degenerate electron gas incorporates the effect of quantum spacetime fluctuations (via a modified dispersion relation) even when the strength of the fluctuations is taken to be very small. In this paper, we show that this Newtonian “super-stability” does not hold true when the gravity is treated in the general relativistic framework. Employing dynamical instability analysis, we find that the Chandrasekhar limit can be reassured even for a range of high strengths of quantum spacetime fluctuations with the onset density for gravitational collapse practically remaining unaffected.

Authors: Ofer AharonyErez Y. UrbachMaya Weiss

We construct holographic backgrounds that are dual by the AdS/CFT correspondence to Euclidean conformal field theories on products of spheres $S^{d_1}\times S^{d_2}$, for conformal field theories whose dual may be approximated by classical Einstein gravity (typically these are large $N$ strongly coupled theories). For $d_2=1$ these backgrounds correspond to thermal field theories on $S^{d_1}$, and Hawking and Page found that there are several possible bulk solutions, with two different topologies, that compete with each other, leading to a phase transition as the relative size of the spheres is modified. By numerically solving the Einstein equations we find similar results also for $d_2>1$, with bulk solutions in which either one or the other sphere shrinks to zero smoothly at a minimal value of the radial coordinate, and with a first order phase transition (for $d_1+d_2 < 9$) between solutions of two different topologies as the relative radius changes. For a critical ratio of the radii there is a (sub-dominant) singular solution where both spheres shrink, and we analytically analyze the behavior near this radius. For $d_1+d_2 < 9$ the number of solutions grows to infinity as the critical ratio is approached.

2019年8月9日 星期五 上午12:22 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Dougherty, John (2019) Sizing up gauge. In: UNSPECIFIED.
2019年8月8日 星期四 下午6:00 | Lixiang Chen, Tianlong Ma, Xiaodong Qiu, Dongkai Zhang, Wuhong Zhang, and Robert W. Boyd | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Lixiang Chen, Tianlong Ma, Xiaodong Qiu, Dongkai Zhang, Wuhong Zhang, and Robert W. Boyd

Correlations between the radial position and radial momentum of entangled photons demonstrate the suitability of these properties for quantum information applications.


[Phys. Rev. Lett. 123, 060403] Published Thu Aug 08, 2019

2019年8月8日 星期四 上午1:42 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Pernu, Tuomas K. (2017) Can physics make us free? Frontiers in Physics, 5:64.
2019年8月6日 星期二 下午6:00 | Roei Remez, Aviv Karnieli, Sivan Trajtenberg-Mills, Niv Shapira, Ido Kaminer, Yossi Lereah, and Ady Arie | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Roei Remez, Aviv Karnieli, Sivan Trajtenberg-Mills, Niv Shapira, Ido Kaminer, Yossi Lereah, and Ady Arie

We investigate, both experimentally and theoretically, the interpretation of the free-electron wave function using spontaneous emission. We use a transversely wide single-electron wave function to describe the spatial extent of transverse coherence of an electron beam in a standard transmission elec…

[Phys. Rev. Lett. 123, 060401] Published Tue Aug 06, 2019

2019年8月6日 星期二 下午3:31 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Suárez, Mauricio (2017) Propensities, Probabilities, and Experimental Statistics. In: UNSPECIFIED.
2019年8月6日 星期二 下午3:30 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Healey, Richard (2019) Beyond Bell? [Preprint]
2019年8月6日 星期二 上午8:00 | Latest Results for Foundations of Physics

Abstract

Is change missing in Hamiltonian Einstein–Maxwell theory? Given the most common definition of observables (having weakly vanishing Poisson bracket with each first-class constraint), observables are constants of the motion and nonlocal. Unfortunately this definition also implies that the observables for massive electromagnetism with gauge freedom (‘Stueckelberg’) are inequivalent to those of massive electromagnetism without gauge freedom (‘Proca’). The alternative Pons–Salisbury–Sundermeyer definition of observables, aiming for Hamiltonian–Lagrangian equivalence, uses the gauge generator G, a tuned sum of first-class constraints, rather than each first-class constraint separately, and implies equivalent observables for equivalent massive electromagnetisms. For General Relativity, G generates 4-dimensional Lie derivatives for solutions. The Lie derivative compares different space-time points with the same coordinate value in different coordinate systems, like 1 a.m. summer time versus 1 a.m. standard time, so a vanishing Lie derivative implies constancy rather than covariance. Requiring equivalent observables for equivalent formulations of massive gravity confirms that Gmust generate the 4-dimensional Lie derivative (not 0) for observables. These separate results indicate that observables are invariant under internal gauge symmetries but covariant under external gauge symmetries, but can this bifurcated definition work for mixed theories such as Einstein–Maxwell theory? Pons, Salisbury and Shepley have studied G for Einstein–Yang–Mills. For Einstein–Maxwell, both \(F_{\mu \nu }\) and \(g_{\mu \nu }\) are invariant under electromagnetic gauge transformations and covariant (changing by a Lie derivative) under 4-dimensional coordinate transformations. Using the bifurcated definition, these quantities count as observables, as one would expect on non-Hamiltonian grounds.

2019年8月5日 星期一 上午1:01 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Gao, Shan (2019) Are Human Brains Quantum Computers? Why Quantum Cognition Says Yes. [Preprint]
2019年8月5日 星期一 上午1:00 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Romano, Davide (2019) A Proposal for the Classical Limit in Bohm’s Theory. In: UNSPECIFIED.
2019年8月5日 星期一 上午12:57 | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0)
Kastner, Ruth (2019) Unitary-Only Quantum Theory Cannot Consistently Describe the Use of Itself: On the Frauchiger-Renner Paradox. [Preprint]

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