# Weekly Papers on Quantum Foundations (15,16)

Authors: Thomas K. GilbertAndrew J. Loveridge

Research in Theoretical Quantum Gravity has continued expansively even as it has become detached from classic arbiters of research such as direct empirical falsification. This makes it an interesting test case for social-scientific theories of what motivates and mediates contemporary scientific research and the nature of scientific objectivity. For our empirical investigation, we conducted 50 semi-structured interviews with researchers in the rival camps of String Theory and Loop Quantum Gravity, coded a subset for reoccurring themes, and subjected the resulting data to statistical analysis. Theoretically, we mobilize aspects of Daston and Galison’s depiction of the scientific self and its relation to epistemic virtues, Pierre Bourdieu’s field-centered account of social space, and Kantian notions of aesthetics in order to delineate the subjective tastes and the related process of collective consensus-making in contemporary quantum gravity research. We make two key contributions. First, our analysis sheds light on the inner workings of the field by connecting its internal epistemic struggles with relevant social-scientific theories. For example, we are able to suggest an explanation for how one approach, String Theory, has become so dominant. Second, our application of theories of social reproduction to the substance of scientific inquiry merits some substantive generalizations to Daston and Galison’s framework. Most significantly, we propose as an addendum to their progression the notion of objectivity through intersubjectivity: objectivity obtained not through the suppression of the self but by its (regulated) pluralistic expression and performance.

 上午8:42 | physics.hist-ph updates on arXiv.org

Authors: Chrysovalantis Stergiou

In this paper we attempt to explicate Salmon’s idea of a causal process, as defined in terms of the mark method, in the context of C*-dynamical systems. We prove two propositions, one establishing mark manifestation infinitely many times along a given interval of the process, and, a second one, which establishes continuous manifestation of mark with the exception of a countable number of isolated points. Furthermore, we discuss how these results can be implemented in the context of Haag-Araki theories of relativistic quantum fields in Minkowski spacetime.

 上午8:42 | physics.hist-ph updates on arXiv.org

Authors: Christian de RondeCésar Massri

In this paper we provide arguments against the tenability of the notion of pure sate within the orthodox textbook account of quantum mechanics. After discussing the meaning of state in physical theories we address its inconsistent reference within the theory of quanta. We will argue that this inconsistency, responsibility of the 20th Century empirical-positivist re-foundation of physics, has been also extended to the notion of pure state. Through the derivation of a theorem we attempt to show the non-equivalence between two different definitions uncritically applied within the specialized literature. While operational purity provides a basis-dependent definition which makes reference to the certain predictions of measurement outcomes, trace-invariant purity provides a purely abstract invariant definition which lacks a direct operational content. We end the paper with a discussion of a possible way out of this metaphysical conundrum through an intensive interpretation of the Born rule which goes beyond its widespread reference to measurement outcomes.

Authors: Christian de RondeCésar Massri

In a recent paper [12], we discussed the serious inconsistency present within the operational and mathematical definition(s) of the notion of pure state. Continuing this analysis, in this work we attempt to address the role of ‘purity’ and ‘mixtures’ within two different categorical approaches to QM, namely, the topos approach originally presented by Chris Isham and Jeremy Butterfield [27, 28, 29] and the more recent logos categorical approach presented by the authors of this article [10, 11, 13]. While the first approach exposes the difficulties to produce a consistent understanding of pure states and mixtures, the latter approach presents a new scheme in which their reference is erased right from the start in favor of an intensive understanding of projection operators and quantum superpositions. This new account of the theory, grounded on an intensive interpretation of the Born rule, allows us not only to avoid the orthodox interpretation of projection operators –either as referring to definite valued properties or measurement outcomes– but also to consider all matrices (of any rank) on equal footing. It is from this latter standpoint that we conclude that instead of distinguishing between pure and mixed states it would be recommendable –for a proper understanding of the theory of quanta– to return to the original matrix formulation of quantum mechanics presented by Werner Heisenberg in 1925.

After a quantum phase transition the quantum vacuum can break up to form classical topological defects. We examine this process for scalar field models with $Z_2$ symmetry for different quench rates for the phase transition. We find that the number density of kinks at late times universally scales as $C (mt)^{-1/2}$ where $m$ is a mass scale in the model and $C\approx 0.25$; it does not depend on the quench timescale in contrast to the Kibble-Zurek scaling for thermal phase transitions. A subleading correction $\propto t^{-3/2}$ to the kink density depends on the details of the phase transition.

 上午8:41 | Maximilian Schlosshauer | quant-ph updates on arXiv.org

We study the protective measurement of a qubit by a second qubit acting as a probe. Consideration of this model is motivated by the possibility of its experimental implementation in multiqubit systems such as trapped ions. In our scheme, information about the expectation value of an arbitrary observable of the system qubit is encoded in the rotation of the state of the probe qubit. We describe the structure of the Hamiltonian that gives rise to this measurement and analyze the resulting dynamics under a variety of realistic conditions, such as noninfinitesimal measurement strengths, repeated measurements, non-negligible intrinsic dynamics of the probe, and interactions of the system and probe qubits with an environment. We propose an experimental realization of our model in an ion trap. The experiment may be performed with existing technology and makes use of established experimental methods for the engineering and control of Hamiltonians for quantum gates and quantum simulations of spin systems.

 上午8:41 | Raymond S. Mackintosh | quant-ph updates on arXiv.org

The identification of `measurement’ in QM as a human action is a source of profound confusion. We propose a solution of the measurement problem based on a reconsideration of the nature of particles. The solution is presented with an idealized model involving the non-locality implicit in the standard interpretation of single slit (or hole) diffraction, as identified in 1927 by Einstein.

 上午8:41 | Giacomo Mauro D’Ariano, Marco Erba, Paolo Perinotti | quant-ph updates on arXiv.org

We investigate operational probabilistic theories where the pure states of every system are the vertices of a simplex. A special case of such theories is that of classical theories, i.e. simplicial theories whose pure states are jointly perfectly discriminable. The usual Classical Theory satisfies also local discriminability. However, simplicial theories—including the classical ones—can violate local discriminability, thus admitting of entangled states. First, we prove sufficient conditions for the presence of entangled states in arbitrary probabilistic theories. Then, we prove that simplicial theories are necessarily causal, and this represents a no-go theorem for conceiving non-causal classical theories. We then provide necessary and sufficient conditions for simplicial theories to exhibit entanglement, and classify their system-composition rules. We conclude proving that, in simplicial theories, an operational formulation of the superposition principle cannot be satisfied, and that—under the hypothesis of $n$-local discriminability—no mixed state admits of a purification. Our results hold also in the general case where the sets of states fail to be convex.

 上午8:41 | Ayan Mitra, Pritam Chattopadhyay, Goutam Paul, Vasilios Zarikas | quant-ph updates on arXiv.org

Various techniques to tackle the black hole information paradox have been proposed. A new way out to tackle the paradox is via the use of pseudo density operator. This approach has successfully dealt the problem with a two qubit entangle system for a single black hole. In this paper, we present the interaction with a binary black hole system by using an arrangement of the three qubit system of Greenberger Horne Zeilinger (GHZ) state. We show that our results are in excellent agreement with the theoretical value. We have also studied the interaction between the two black holes by considering the correlation between the qubits in the binary black hole system. The results depict a complete agreement with the proposed model. In addition to the verification, we also propose how modern detection of gravitational waves can be used on our optical setup as an input source, thus bridging the gap with the gravitational wave’s observational resources in terms of studying black hole properties with respect to quantum information and entanglement.

Authors: John R. Klauder

For purposes of quantization, classical gravity is normally expressed by canonical variables, namely the metric $g_{ab}(x)$ and the momentum $\pi^{cd}(x)$. Canonical quantization requires a proper promotion of these classical variables to quantum operators, which, according to Dirac, the favored operators should be those arising from classical variables that formed Cartesian coordinates; sadly, in this case, that is not possible. However, an affine quantization features promoting the metric $g_{ab}(x)$ and the momentric $\pi^c_d(x)\;[\equiv \pi^{ce}(x) \,g_{de}(x)]$ to operators. Instead of these classical variables belonging to a constant zero curvature space (i.e., instead of a flat space), they belong to a space of constant negative curvatures. This feature may even have its appearance in black holes, which could strongly point toward an affine quantization approach to quantize gravity.

Authors: Joshua FooSho OnoeMagdalena Zych

Unruh-deWitt detectors have been utilised widely as probes for quantum particles, entanglement and spacetime curvature. Here, we extend the standard treatment of an Unruh-deWitt detector interacting with a massless, scalar field to include the detector travelling in a quantum superposition of classical trajectories. We derive perturbative expressions for the final state of the detector, and show that it depends on field correlation functions evaluated locally along the individual trajectories, as well as non-locally between the superposed trajectories. By applying our general approach to a detector travelling in a superposition of two uniformly accelerated trajectories, including those with equal and differing proper accelerations, we discover novel interference effects in the emission and absorption spectra. These effects can be traced to causal relations between the superposed trajectories. Finally, we show that in general, such a detector does not thermalise even if the superposed paths would individually yield the same thermal state.

 2020年4月17日 星期五 上午8:00 | Latest Results for Synthese

### Abstract

Presentists argue that only the present is real. In this paper, I ask what duration the present has on a presentist’s account. While several answers are available, each of them requires the adoption of a measure and, with that adoption, additional work must be done to define the present. Whether presentists conclude (1) that a reductionist account of duration is acceptable, (2) that duration is not an applicable concept for their notion of the present, (3) that the present has a duration of zero, or that (4) that the present has a duration, a more robust account of the present is required. I suggest that some of the most difficult questions about duration can be avoided at the cost of no longer viewing presentism as a theory about time, but rather as a theory about existence. In the conclusion, I suggest an interpretation of presentism that allows it to endorse the view that time is nothing more than the measure of change.

 2020年4月17日 星期五 上午8:00 | Latest Results for Synthese

### Abstract

In prior work, we have argued that spacetime functionalism provides tools for clarifying the conceptual difficulties specifically linked to the emergence of spacetime in certain approaches to quantum gravity. We argue in this article that spacetime functionalism in quantum gravity is radically different from other functionalist approaches that have been suggested in quantum mechanics and general relativity: in contrast to these latter cases, it does not compete with purely interpretative alternatives, but is rather intertwined with the physical theorizing itself at the level of quantum gravity. Spacetime functionalism allows one to articulate a coherent realist perspective in the context of quantum gravity, and to relate it to a straightforward realist understanding of general relativity.

 2020年4月17日 星期五 上午8:00 | Latest Results for Synthese

### Abstract

What it would take to vindicate folk temporal error theory? This question is significant against a backdrop of new views in quantum gravity—so-called timeless physical theories—that claim to eliminate time by eliminating a one-dimensional substructure of ordered temporal instants. Ought we to conclude that if these views are correct, nothing satisfies the folk concept of time and hence that folk temporal error theory is true? In light of evidence we gathered, we argue that physical theories that entirely eliminate an ordered substructure vindicate folk temporal error theory.

 2020年4月16日 星期四 下午4:47 | ScienceDirect Publication: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsScienceDirect RSShttps://www.sciencedirect.com/journal/studies-in-history-and-philosophy-of-science-part-b-studies-in-history-and-philosophy-of-modern-physicsRSS for NodeWed, 24 Jul 2019 09:46:42 GMTCopyright © 2019 Elsevier Ltd. All rights reservedImprints of the underlying structure of physical theoriesPublication date: Available online 12 July 2019Source: Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern PhysicsAuthor(s): Jorge ManeroAbstractIn the context of scientific realism, this paper intends to provide a formal and accurate description of the structural-based ontology posited by classical mechanics, quantum mechanics and special relativity, which is preserved across the empirical domains of these theories and explain their successful predictions. Along the lines of ontic structural realism, such a description is undertaken by

Publication date: Available online 9 April 2020

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

 2020年4月16日 星期四 下午4:47 | gr-qc updates on arXiv.org

Authors: Taha A MalikRafael Lopez-Mobilia

Typically, the entropy of an isolated system in equilibrium is calculated by counting the number of accessible microstates, or in more general cases by using the Gibbs formula. In irreversible processes entropy spontaneously increases and this is understood from statistical arguments. We propose a new measure of entropy based on the level of irreversibility of a process. This formulation agrees in first approximation with the usual methods of calculating entropy and can be readily applied in the case of a black hole in the semiclassical regime.

The star S2 orbiting the compact radio source Sgr A* is a precision probe of the gravitational field around the closest massive black hole (candidate). Over the last 2.7 decades we have monitored the star’s radial velocity and motion on the sky, mainly with the SINFONI and NACO adaptive optics (AO) instruments on the ESO VLT, and since 2017, with the four-telescope interferometric beam combiner instrument GRAVITY. In this paper we report the first detection of the General Relativity (GR) Schwarzschild Precession (SP) in S2’s orbit. Owing to its highly elliptical orbit (e = 0.88), S2’s SP is mainly a kink between the pre-and post-pericentre directions of motion ~ +- 1 year around pericentre passage, relative to the corresponding Kepler orbit. The superb 2017-2019 astrometry of GRAVITY defines the pericentre passage and outgoing direction. The incoming direction is anchored by 118 NACO-AO measurements of S2’s position in the infrared reference frame, with an additional 75 direct measurements of the S2-Sgr A* separation during bright states (‘flares’) of Sgr A*. Our 14-parameter model fits for the distance, central mass, the position and motion of the reference frame of the AO astrometry relative to the mass, the six parameters of the orbit, as well as a dimensionless parameter f_SP for the SP (f_SP = 0 for Newton and 1 for GR). From data up to the end of 2019 we robustly detect the SP of S2, del phi = 12′ per orbital period. From posterior fitting and MCMC Bayesian analysis with different weighting schemes and bootstrapping we find f_SP = 1.10 +- 0.19. The S2 data are fully consistent with GR. Any extended mass inside S2’s orbit cannot exceed ~ 0.1% of the central mass. Any compact third mass inside the central arcsecond must be less than about 1000 M_sun.

 2020年4月16日 星期四 下午4:47 | gr-qc updates on arXiv.org

Authors: Pujian MaoWen-Di Tan

We present a unified investigation of memory effect in Einstein-Maxwell theory. Our result recovers the two known gravitational memory effects and the two known electromagnetic memory effects.

 2020年4月16日 星期四 下午4:47 | gr-qc updates on arXiv.org

Until recently, table-top tests of quantum gravity (QG) were thought to be practically impossible. However, due to a radical new approach to testing QG that uses principles of quantum information theory (QIT) and quantum technology, such tests now seem, remarkably, within sight. In particular, a promising test has been proposed where the generation of entanglement between two massive quantum systems, both in a superposition of two locations, would provide evidence of QG. In QIT, quantum information can be encoded in discrete variables, such as qubits, or continuous variables. The latter approach, called continuous-variable QIT (CVQIT), is extremely powerful as it has been very effective in applying QIT to quantum field theory. Here we apply CVQIT to QG, and show that another signature of QG would be the creation of non-Gaussianity, a continuous-variable resource that is necessary for universal quantum computation. In contrast to entanglement, non-Gaussianity can be applied to a single rather than multi-partite quantum system, and does not rely on local interactions. We use these attributes to describe a table-top test of QG that is based on just a single quantum system in a single location.

Authors: Roman Krzanowski

The note discusses the concept of meaningful, physical information presented by Carlo Rovelli. It points out certain consequences of the information model not elucidated in the original paper but important to its comprehensive understanding.

 2020年4月15日 星期三 上午8:00 | Latest Results for Foundations of Physics

The authors would like to make the corrections to the original article described below.

 2020年4月9日 星期四 下午6:00 | Paola Ruggiero, Pasquale Calabrese, Benjamin Doyon, and Jérôme Dubail | PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Author(s): Paola Ruggiero, Pasquale Calabrese, Benjamin Doyon, and Jérôme Dubail

Physical systems made of many interacting quantum particles can often be described by Euler hydrodynamic equations in the limit of long wavelengths and low frequencies. Recently such a classical hydrodynamic framework, now dubbed generalized hydrodynamics (GHD), was found for quantum integrable mode…

[Phys. Rev. Lett. 124, 140603] Published Thu Apr 09, 2020

 2020年4月9日 星期四 上午8:00 | Latest Results for Foundations of Physics

### Abstract

The problem of constructing maximal equiangular tight frames or SICs was raised by Zauner in 1998. Four years ago it was realized that the problem is closely connected to a major open problem in number theory. We discuss why such a connection was perhaps to be expected, and give a simplified sketch of some developments that have taken place in the past 4 years. The aim, so far unfulfilled, is to prove existence of SICs in an infinite sequence of dimensions.

 2020年4月8日 星期三 上午8:00 | Latest Results for Foundations of Physics

### Abstract

This paper shows that the ClauserHorneShimonyHolt test of locality of correlations which was originally designed to be used with binary observables can actually be used for any couples of quantum-like bounded continuous observables, and then for any experimental situation describable within the mathematical framework of quantum theory.