Latest Papers on Quantum Foundations - Updated Daily by IJQF

Experimental certification of millions of genuinely entangled atoms in a solid

Nature Communications, Published online: 13 October 2017; doi:10.1038/s41467-017-00898-6

The presence of entanglement in macroscopic systems is notoriously difficult to observe. Here, the authors develop a witness which allow them to demonstrate entanglement between millions of atoms in a solid-state quantum memory prepared by the heralded absorption of a single photon.

Authors: Leonardo Modesto, Yun Soo Myung, Sang-Heon Yi

In this paper we prove the universal nature of the Unruh effect in a general class of weakly non-local field theories.

At the same time we solve the tension between two conflicting claims published in literature.

Our universality statement is based on two independent computations based on the canonical formulation as well as path integral formulation of the quantum theory.

Authors: Giuseppe Castagnoli

A bare description of the seminal quantum algorithm devised by Deutsch could mean more than an introduction to quantum computing. It could contribute to opening the field to interdisciplinary research.

One-dimensional topological superconductors host Majorana zero modes (MZMs), the non-local property of which could be exploited for quantum computing applications. We use spin-polarized scanning tunneling microscopy to show that MZMs realized in self-assembled Fe chains on the surface of Pb have a spin polarization that exceeds that stemming from the magnetism of these chains. This feature, captured by our model calculations, is a direct consequence of the nonlocality of the Hilbert space of MZMs emerging from a topological band structure. Our study establishes spin polarization measurements as a diagnostic tool to distinguish topological MZMs from trivial in-gap states of a superconductor.

Authors: Sanjib Dey, Anha Bhat, Davood Momeni, Mir Faizal, Ahmed Farag Ali, Tarun Kumar Dey, Atikur Rehman

One of the major difficulties of modern science underlies at the unification of general relativity and quantum mechanics. Different approaches towards such theory have been proposed. Noncommutative theories serve as the root of almost all such approaches. However, the identification of the appropriate passage to quantum gravity is suffering from the inadequacy of experimental techniques. It is beyond our ability to test the effects of quantum gravity thorough the available scattering experiments, as it is unattainable to probe such high energy scale at which the effects of quantum gravity appear. Here we propose an elegant alternative scheme to test such theories by detecting the deformations emerging from the noncommutative structures. Our protocol relies on the novelty of an opto-mechanical experimental setup where the information of the noncommutative oscillator is exchanged via the interaction with an optical pulse inside an optical cavity. We also demonstrate that our proposal is within the reach of current technology and, thus, it could uncover a feasible route towards the realization of quantum gravitational phenomena thorough a simple table-top experiment.

Authors: Ivan Glasser, Nicola Pancotti, Moritz August, Ivan D. Rodriguez, J. Ignacio Cirac

Neural Networks Quantum States have been recently introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between Neural Networks Quantum States in the form of Restricted Boltzmann Machines and some classes of Tensor Network states in arbitrary dimension. In particular we demonstrate that short-range Restricted Boltzmann Machines are Entangled Plaquette States, while fully connected Restricted Boltzmann Machines are String-Bond States with a non-local geometry and low bond dimension. These results shed light on the underlying architecture of Restricted Boltzmann Machines and their efficiency at representing many-body quantum states. String-Bond States also provide a generic way of enhancing the power of Neural Networks Quantum States and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of Tensor Networks and the efficiency of Neural Network Quantum States into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional Tensor Networks, we show that Neural Networks Quantum States and their String-Bond States extension can describe a lattice Fractional Quantum Hall state exactly. In addition, we provide numerical evidence that Neural Networks Quantum States can approximate a chiral spin liquid with better accuracy than Entangled Plaquette States and local String-Bond States. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of String-Bond States as a tool in more traditional machine learning applications.

Authors: W. David Wick

In the first paper of this series, I introduced a non-linear, Hamiltonian, generalization of Schroedinger's theory that blocks formation of macroscopic dispersion ("cats"). But that theory was entirely deterministic, and so the origin of random outcomes in experiments such as Stern-Gerlach or EPRB was left open. Here I propose that Schroedinger's wavefunction has a random component and demonstrate that such an improvised stochastic theory can violate Bell's inequality. Repeated measurements and the back-reaction on the microsystem are discussed in a toy example. Experiments that might falsify the theory are described.

Allori, Valia (2017) Scientific Realism and Primitive Ontology Or: The Pessimistic Induction and the Nature of the Wave Function. [Preprint]
Allori, Valia (2017) A New Argument for the Nomological Interpretation of the Wave Function: The Galilean Group and the Classical Limit of Nonrelativistic Quantum Mechanics. [Preprint]
Wallace, David (2017) Why Black Hole Information Loss is Paradoxical. [Preprint]

We review aspects of twistor theory, its aims and achievements spanning the last five decades. In the twistor approach, space–time is secondary with events being derived objects that correspond to compact holomorphic curves in a complex threefold—the twistor space. After giving an elementary construction of this space, we demonstrate how solutions to linear and nonlinear equations of mathematical physics—anti-self-duality equations on Yang–Mills or conformal curvature—can be encoded into twistor cohomology. These twistor correspondences yield explicit examples of Yang–Mills and gravitational instantons, which we review. They also underlie the twistor approach to integrability: the solitonic systems arise as symmetry reductions of anti-self-dual (ASD) Yang–Mills equations, and Einstein–Weyl dispersionless systems are reductions of ASD conformal equations. We then review the holomorphic string theories in twistor and ambitwistor spaces, and explain how these theories give rise to remarkable new formulae for the computation of quantum scattering amplitudes. Finally, we discuss the Newtonian limit of twistor theory and its possible role in Penrose’s proposal for a role of gravity in quantum collapse of a wave function.


Multi-time wave functions are wave functions for multi-particle quantum systems that involve several time variables (one per particle). In this paper we contrast them with solutions of wave equations on a space–time with multiple timelike dimensions, i.e., on a pseudo-Riemannian manifold whose metric has signature such as \({+}{+}{-}{-}\) or \({+}{+}{-}{-}{-}{-}{-}{-}\) , instead of \({+}{-}{-}{-}\) . Despite the superficial similarity, the two behave very differently: whereas wave equations in multiple timelike dimensions are typically mathematically ill-posed and presumably unphysical, relevant Schrödinger equations for multi-time wave functions possess for every initial datum a unique solution on the spacelike configurations and form a natural covariant representation of quantum states.

Authors: Mario Hubert, Davide Romano

It is generally argued that if the wave-function in the de Broglie--Bohm theory is a physical field, it must be a field in configuration space. Nevertheless, it is possible to interpret the wave-function as a multi-field in three-dimensional space. This approach hasn't received the attention yet it really deserves. The aim of this paper is threefold: first, we show that the wave-function is naturally and straightforwardly construed as a multi-field; second, we show why this interpretation is superior to other field interpretations; third, we clarify common misconceptions.

Authors: Manaka Okuyama, Masayuki Ohzeki

The quantum speed limit (QSL), or the energy-time uncertainty relation, describes the fundamental maximum rate for quantum time evolution and has been regarded as being unique in quantum mechanics. In this study, we obtain a classical speed limit corresponding to the QSL using the Hilbert space for the classical Liouville equation. Thus, classical mechanics has a fundamental speed limit, and QSL is not a purely quantum phenomenon but a universal dynamical property of the Hilbert space. Furthermore, we obtain similar speed limits for the imaginary-time Schroedinger equations such as the master equation.

Authors: Patrick Rebentrost, Thomas R. Bromley, Christian Weedbrook, Seth Lloyd

Quantum computing allows for the potential of significant advancements in both the speed and the capacity of widely-used machine learning algorithms. In this paper, we introduce quantum algorithms for a recurrent neural network, the Hopfield network, which can be used for pattern recognition, reconstruction, and optimization as a realization of a content addressable memory system. We show that an exponentially large network can be stored in a polynomial number of quantum bits by encoding the network into the amplitudes of quantum states. By introducing a new classical technique for operating such a network, we can leverage quantum techniques to obtain a quantum computational complexity that is logarithmic in the dimension of the data. This potentially yields an exponential speed-up in comparison to classical approaches. We present an application of our method as a genetic sequence recognizer.

Authors: W. David Wick

Working entirely within the Schroedinger paradigm, meaning wavefunction only, I present a modification of his theory that prevents formation of macroscopic dispersion (MD; "cats"). The proposal is to modify the Hamiltonian based on a method introduced by Steven Weinberg in 1989, as part of a program to test quantum mechanics at the atomic or nuclear level. By contrast, the intent here is to eliminate MD without affecting the predictions of quantum mechanics at the microscopic scale. This restores classical physics at the macro level. Possible experimental tests are indicated and the differences from previous theories discussed. In a second paper, I will address the other difficulty of wavefunction physics without the statistical (Copenhagen) interpretation: how to explain random outcomes in experiments such as Stern-Gerlach, and whether a Schroedingerist theory with a random component can violate Bell's inequality.

Hubert, Mario and Romano, Davide (2017) The Wave-Function Is a Multi-Field. [Preprint]
de Ronde, Christian and Massri, Cesar (2014) Kochen-Specker Theorem, Physical Invariance and Quantum Individuality. [Preprint]
Publication date: Available online 9 October 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Eleanor Knox
This paper looks at the relationship between spacetime functionalism and Harvey Brown's dynamical relativity. One popular way of reading and extending Brown's programme in the literature rests on viewing his position as a version of relationism. But a kind of spacetime functionalism extends the project in a different way, by focussing on the account Brown gives of the role of spacetime in relativistic theories. It is then possible to see this as giving a functional account of the concept of spacetime which may be applied to theories that go beyond relativity. This paper explores the way in which both the relationist project and the functionalist project relate to Brown's work, despite being incompatible. Ultimately, these should not be seen as two conflicting readings of Brown, but two different directions in which to take his project.

Author(s): F. Duncan M. Haldane

The 2016 Nobel Prize for Physics was shared by David J. Thouless, F. Duncan M. Haldane, and John Michael Kosterlitz. These papers are the text of the address given in conjunction with the award.

[Rev. Mod. Phys. 89, 040502] Published Mon Oct 09, 2017

Caponigro, Michele (2017) Quantum Entanglement and Uncertainty Principle. [Preprint]
Caponigro, Michele (2017) Quantum Mechanics: philosophy and Interpretations. [Preprint]
Wallace, David (2017) The Case for Black Hole Thermodynamics, Part II: Statistical Mechanics. [Preprint]
Wallace, David (2017) The Case for Black Hole Thermodynamics, Part I: Phenomenological Thermodynamics. [Preprint]
Caponigro, Michele (2017) Many-Worlds Interpretation and Quantum Entanglement. [Preprint]
Caponigro, Michele (2017) Quantum Entanglement vs Non-Locality. [Preprint]
Caponigro, Michele (2017) Philosophy and Interpretations of Quantum Non-Locality. [Preprint]
Caponigro, Michele (2017) Quantum Entanglement:epistemological overview. [Preprint]
Caponigro, Michele (2017) Reality as Information? [Preprint]
Caponigro, Michele (2017) The nature of Reality: Einstein-Podolsky-Rosen Argument in QM. [Preprint]
Caponigro, Michele (2017) Quantum Mechanics: Observer and von Neumann Chain. [Preprint]


In a recent paper on Foundations of Physics, Stephen Boughn reinforces a view that is more shared in the area of the foundations of quantum mechanics than it would deserve, a view according to which quantum mechanics does not require nonlocality of any kind and the common interpretation of Bell theorem as a nonlocality result is based on a misunderstanding. In the present paper I argue that this view is based on an incorrect reading of the presuppositions of the EPR argument and the Bell theorem and, as a consequence, is unfounded.

Palacios, Patricia (2017) Phase Transitions: A Challenge for Reductionism? [Preprint]
Kastner, Ruth and Kauffman, Stuart and Epperson, Michael (2017) Taking Heisenberg's Potentia Seriously. [Preprint]
Ardourel, Vincent and Guay, Alexandre (2017) Why is the transference theory of causation insuffcient? The challenge of the Aharonov-Bohm effect. [Preprint]


I examine the relationship between \((d+1)\) -dimensional Poincaré metrics and d-dimensional conformal manifolds, from both mathematical and physical perspectives. The results have a bearing on several conceptual issues relating to asymptotic symmetries in general relativity and in gauge–gravity duality, as follows: (1: Ambient Construction)  I draw from the remarkable work by Fefferman and Graham (Elie Cartan et les Mathématiques d’aujourd’hui, Astérisque, 1985; The Ambient Metric. Annals of Mathematics Studies, Princeton University Press, Princeton, 2012) on conformal geometry, in order to prove two propositions and a theorem that characterise which classes of diffeomorphisms qualify as gravity-invisible. I define natural notions of gravity-invisibility (strong, weak, and simpliciter) that apply to the diffeomorphisms of Poincaré metrics in any dimension. (2: Dualities) I apply the notions of invisibility, developed in (1), to gauge–gravity dualities: which, roughly, relate Poincaré metrics in \(d+1\) dimensions to QFTs in d dimensions. I contrast QFT-visible versus QFT-invisible diffeomorphisms: those gravity diffeomorphisms that can, respectively cannot, be seen from the QFT. The QFT-invisible diffeomorphisms are the ones which are relevant to the hole argument in Einstein spaces. The results on dualities are surprising, because the class of QFT-visible diffeomorphisms is larger than expected, and the class of QFT-invisible ones is smaller than expected, or usually believed, i.e. larger than the PBH diffeomorphisms in Imbimbo et al. (Class Quantum Gravity 17(5):1129, 2000, Eq. 2.6). I also give a general derivation of the asymptotic conformal Killing equation, which has not appeared in the literature before.

Authors: Alan A. Coley

We present a list of open questions in mathematical physics. After a historical introduction, a number of problems in a variety of different fields are discussed, with the intention of giving an overall impression of the current status of mathematical physics, particularly in the topical fields of classical general relativity, cosmology and the quantum realm. This list is motivated by the recent article proposing 42 fundamental questions (in physics) which must be answered on the road to full enlightenment. But paraphrasing a famous quote by the British football manager Bill Shankly, in response to the question of whether mathematics can answer the Ultimate Question of Life, the Universe, and Everything, mathematics is, of course, much more important than that.

Authors: Edward Witten

I discuss gauge and global symmetries in particle physics, condensed matter physics, and quantum gravity. In a modern understanding, global symmetries are approximate and gauge symmetries may be emergent. (Based on a lecture at the April, 2016 meeting of the American Physical Society in Salt Lake City, Utah.)

Authors: K. Piscicchia, A. Bassi, C. Curceanu, R. Del Grande, S. Donadi, B.C. Hiesmayr, A. Pichler

In this paper, new upper limits on the parameters of the Continuous Spontaneous Localization (CSL) collapse model are extracted. To this end, the X-ray emission data collected by the IGEX collaboration are analyzed and compared with the spectrum of the spontaneous photon emission process predicted by collapse models.

This study allows the obtainment of the most stringent limits within a relevant range of the CSL model parameters, with respect to any other method. The collapse rate $\lambda$ and the correlation length $r_C$ are mapped, thus allowing the exclusion of a broad range of the parameter space.

Authors: Mohammad Hossein Zarei, Afshin Montakhab

The correspondence between classical spin models and quantum states has attracted much attention in recent years. However, it remains an open problem as to which specific spin model a given (well-known) quantum state maps to. In this Letter, we provide such an explicit correspondence for an important class of quantum states where a duality relation is proved between classical spin models and quantum Calderbank-Shor-Steane (CSS) states. In particular, we employ graph-theoretic methods to prove that the partition function of a classical spin model on a hypergraph $H$ is equal to the inner product of a product state with a quantum CSS state on a dual hypergraph $\tilde{H}$. We next use this dual correspondence to prove that the critical behavior of the classical system corresponds to a relative robustness of the corresponding CSS state to bit-flip (and phase-flip) noise, thus called critical robustness. We finally conjecture that such critical robustness is related to the topological order in quantum CSS states, thus providing a possible practical characterization of such states.

The best atomic clock will only be out of sync 3.5 times in every 10 quintillion ticks. It could help test general relativity and hunt for gravitational waves
Publication date: Available online 3 October 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Vladislav Terekhovich
Despite the importance of the variational principles of physics, there have been relatively few attempts to consider them for a realistic framework. In addition to the old teleological question, this paper continues the recent discussion regarding the modal involvement of the principle of least action and its relations with the Humean view of the laws of nature. The reality of possible paths in the principle of least action is examined from the perspectives of the contemporary metaphysics of modality and Leibniz's concept of essences or possibles striving for existence. I elaborate a modal interpretation of the principle of least action that replaces a classical representation of a system's motion along a single history in the actual modality by simultaneous motions along an infinite set of all possible histories in the possible modality. This model is based on an intuition that deep ontological connections exist between the possible paths in the principle of least action and possible quantum histories in the Feynman path integral. I interpret the action as a physical measure of the essence of every possible history. Therefore only one actual history has the highest degree of the essence and minimal action. To address the issue of necessity, I assume that the principle of least action has a general physical necessity and lies between the laws of motion with a limited physical necessity and certain laws with a metaphysical necessity.

Author(s): Clive Emary

Ambiguous measurements do not reveal complete information about the system under test. Their quantum-mechanical counterparts are semiweak (or in the limit, weak) measurements and here we discuss their role in tests of the Leggett-Garg inequalities. We show that, while ambiguous measurements allow on...

[Phys. Rev. A 96, 042102] Published Wed Oct 04, 2017


An influential theory has it that metaphysical indeterminacy occurs just when reality can be made completely precise in multiple ways. That characterization is formulated by employing the modal apparatus of ersatz possible worlds. As quantum physics taught us, reality cannot be made completely precise. I meet the challenge by providing an alternative theory which preserves the use of ersatz worlds but rejects the precisificational view of metaphysical indeterminacy. The upshot of the proposed theory is that it is metaphysically indeterminate whether p just in case it is neither true nor false that p, and no terms in ‘p’ are semantically defective. In other words, metaphysical indeterminacy arises when the world cannot be adequately described by a complete set of sentences defined in a semantically nondefective language. Moreover, the present theory provides a reductive analysis of metaphysical indeterminacy, unlike its influential predecessor. Finally, I argue that any adequate logic of a language with an indeterminate subject matter is neither compositional nor bivalent.

Nature Physics 13, 926 (2017). doi:10.1038/nphys4291

Author: Federico Levi

Authors: J. Abajian, S. Carlip

We investigate the behavior of small subsets of causal sets that approximate Minkowski space in three, four, and five dimensions, and show that their effective dimension decreases smoothly at small distances. The details of the short distance behavior depend on a choice of dimensional estimator, but for a reasonable version of the Myrheim-Meyer dimension, the minimum dimension is $d \approx 2$, reproducing results that have been seen in other approaches to quantum gravity.

Authors: Saurya Das, Matthew P. G. Robbins, Elias C. Vagenas

It is believed that classical behavior emerges in a quantum system due to decoherence. It has also been proposed that gravity can be a source of this decoherence. We examine this in detail by studying a number of quantum systems, including ultra-relativistic and non-relativistic particles, at low and high temperatures in an expanding Universe, and show that this proposal is valid for a large class of quantum systems.

Authors: Roberto Longo

Landauer principle provides a link between Shannon information entropy and Clausius thermodynamical entropy. We set up here a basic formula for the incremental free energy of a quantum channel, possibly relative to infinite systems, naturally arising by an Operator Algebraic point of view. By the Tomita-Takesaki modular theory, we can indeed describe a canonical evolution associated with a quantum channel state transfer. Such evolution is implemented both by a modular Hamiltonian and a physical Hamiltonian, the latter being determined by its functoriality properties. This allows us to make an intrinsic analysis, extending our QFT index formula, but without any a priori given dynamics; the associated incremental free energy is related to the logarithm of the Jones index and is thus quantised. This leads to a general lower bound for the incremental free energy of an irreversible quantum channel which is half of the Landauer bound, and to further bounds corresponding to the discrete series of the Jones index. In the finite dimensional context, or in the case of DHR charges in QFT, where the dimension is a positive integer, our lower bound agrees with Landauer bound.

Authors: A. I. Arbab

By expressing the Schr\"{o}dinger wave function in the form $\psi=Re^{iS/\hbar}$, where $R$ and $S$ are real functions, we have shown that the expectation value of $S$ is conserved. The amplitude of the wave ($R$) is found to satisfy the Schr\"{o}dinger equation while the phase ($S$) is related to the energy conservation. Besides the quantum potential that depends on $R$, \emph{viz.}, $V_Q=-\frac{\hbar^2}{2m}\frac{\nabla^2R}{R}$\,, we have obtained a spin potential $V_S=-\frac{S\nabla^2S}{m}$ that depends on $S$ which is attributed to the particle spin. The spin force is found to give rise to dissipative viscous force. The quantum potential may be attributed to the interaction between the two subfields $S$ and $R$ comprising the quantum particle. This results in splitting (creation/annihilation) of these subfields, each having a mass $mc^2$ with an internal frequency of $2mc^2/\hbar$, satisfying the original wave equation and endowing the particle its quantum nature. The mass of one subfield reflects the interaction with the other subfield. If in Bohmian ansatz $R$ satisfies the Klein-Gordon equation, then $S$ must satisfies the wave equation. Conversely, if $R$ satisfies the wave equation, then $S$ yields the Einstein relativistic energy momentum equation.

Authors: Alexey A. Kryukov

Quantum observables can be identified with vector fields on the sphere of normalized states. The resulting vector representation is used in the paper to undertake a simultaneous treatment of macroscopic and microscopic bodies in quantum mechanics. Components of the velocity and acceleration of state under Schr\"odinger evolution are given for a clear physical interpretation. Solutions to Schr\"odinger and Newton equations are shown to be related beyond the Ehrenfest results on the motion of averages. A formula relating the normal probability distribution and the Born rule is found.

The growing block view of time holds that the past and present are real whilst the future is unreal; as future events become present and real, they are added on to the growing block of reality. Surprisingly, given the recent interest in this view, there is very little literature on its origins. This paper explores those origins, and advances two theses. First, I show that although C. D. Broads (1923)
Scientific Thought provides the first defence of the growing block theory, the theory receives its first articulation in Samuel Alexanders (1920) Space, Time, and Deity. Further, Alexanders account of deity inclines towards the growing block view. Second, I argue that Broad shifted towards the growing block theory as a result of his newfound conviction that time has a direction. By way of tying these theses together, I argue that Broads views on the direction of time and possibly even his growing block theory are sourced in Alexander.

Authors: Marco Roncaglia

According to quantum mechanics, the informational content of isolated systems does not change in time. However, subadditivity of entropy seems to describe an excess of information when we look at single parts of a composite systems and their correlations. Moreover, the balance between the entropic contributions coming from the various parts is not conserved under unitary transformations. Reasoning on the basic concept of quantum mechanics, we find that in such a picture an important term has been overlooked: the intrinsic quantum information encoded in the coherence of pure states. To fill this gap we are led to define a quantity, that we call coherent entropy, which is necessary to account for the "missing" information and for re-establishing its conservation. Interestingly, the coherent entropy is found to be equal to the information conveyed in the future by quantum states. The perspective outlined in this paper may be of some inspiration in several fields, from foundations of quantum mechanics to black-hole physics.

Authors: David Navia

This work is about Bohmian mechanics, a non-relativistic quantum theory about the motion of particles and their trajectories, named after its inventor David Bohm (Bohm,1952). This mechanics resolves all paradoxes associated with the measurement problem in nonrelativistic quantum mechanics. It accounts for quantum randomness, absolute uncertainty, the meaning of the wave function of a system, collapse of the wave function, and familiar (macroscopic) reality. We review the purpose for which Bohmian trajectories were invented: to serve as the foundation of quantum mechanics, i.e., to explain quantum mechanics in terms of a theory that is free of paradoxes and allows an understanding that is as clear as that of classical mechanics. To achieve this we analyse an optical interferometry experiment devised and carried out 2005 by Shahriar Afshar (Afshar,2005). The radical claim of Afshar implies in his own words the 'observation of physical reality in the classical sense' for both 'which path (particle-like)' and 'interference (wave-like)' properties of photons in the same experimental setup through the violation of the Englert-Greenberger duality relation (Englert,1996) that according to Englert can be regarded as quantifying of the 'principle of complementarity'.

Authors: Rainer Collier

This article examines the consequences of the existence of an upper particle momentum limit in quantum electrodynamics, where this momentum limit is the Planck momentum. The method used is Fourier analysis as developed already by Fermi in his fundamental work on the quantum theory of radiation. After determination of the appropriate Hamiltonian, a Schr\"odinger equation and the associated commutation rules of the field operators are given. At the upper momentum limit mentioned above, the divergent terms occurring in the Hamiltonian (the self-energies of the electrons and the zero-point energy of the electromagnetic field) adopt finite values, which will be stated and compared with each other.

Authors: Ekaterina Moreva, Marco Gramegna, Giorgio Brida, Lorenzo Maccone, Marco Genovese

In this paper we provide an experimental illustration of Page and Wootters' quantum time mechanism that is able to describe two-time quantum correlation functions. This allows us to test a Leggett-Garg inequality, showing a violation from the "internal" observer point of view. The "external" observer sees a time-independent global state. Indeed, the scheme is implemented using a narrow-band single photon where the clock degree of freedom is encoded in the photon's position. Hence, the internal observer that measures the position can track the flow of time, while the external observer sees a delocalized photon that has no time evolution in the experiment time-scale.

Authors: Roman Orus, Roger Martin, Juan Uriagereka

Matrix syntax is a formal model of syntactic relations in language. The purpose of this paper is to explain its mathematical foundations, for an audience with some formal background. We make an axiomatic presentation, motivating each axiom on linguistic and practical grounds. The resulting mathematical structure resembles some aspects of quantum mechanics. Matrix syntax allows us to describe a number of language phenomena that are otherwise very difficult to explain, such as linguistic chains, and is arguably a more economical theory of language than most of the theories proposed in the context of the minimalist program in linguistics. In particular, sentences are naturally modeled as vectors in a Hilbert space with a tensor product structure, built from 2x2 matrices belonging to some specific group.

Authors: P. Fernandez de Cordoba, J.M. Isidro

The holographic principle sets an upper bound on the total entropy content of the Universe. Within the limits of a Newtonian approximation, a quantum-mechanical model is presented to describe the cosmological fluid. Under the assumption that gravitational equipotential surfaces can be identified with isoentropic surfaces, this model allows for a simple computation of the gravitational entropy of the Universe. The results thus obtained no longer saturate the holographic bound, thus representing a considerable improvement on previous theoretical estimates.

Authors: Catarina Moreira, Emmanuel Haven, Sandro Sozzo, Andreas Wichert

In this work, we analyse and model a real life financial loan application belonging to a sample bank in the Netherlands. The log is robust in terms of data, containing a total of 262 200 event logs, belonging to 13 087 different credit applications. The dataset is heterogeneous and consists of a mixture of computer generated automatic processes and manual human tasks. The goal is to work out a decision model, which represents the underlying tasks that make up the loan application service, and to assess potential areas of improvement of the institution's internal processes. To this end we study the impact of incomplete event logs for the extraction and analysis of business processes. It is quite common that event logs are incomplete with several amounts of missing information (for instance, workers forget to register their tasks). Absence of data is translated into a drastic decrease of precision and compromises the decision models, leading to biased and unrepresentative results. We investigate how classical probabilistic models are affected by incomplete event logs and we explore quantum-like probabilistic inferences as an alternative mathematical model to classical probability. This work represents a first step towards systematic investigation of the impact of quantum interference in a real life large scale decision scenario. The results obtained in this study indicate that, under high levels of uncertainty, the quantum-like models generate quantum interference terms, which allow an additional non-linear parameterisation of the data. Experimental results attest the efficiency of the quantum-like Bayesian networks, since the application of interference terms is able to reduce the error percentage of inferences performed over quantum-like models when compared to inferences produced by classical models.

Authors: M. C. Diamantini, C. A. Trugenberger

We show that, in discrete models of quantum gravity, emergent geometric space can be viewed as the entanglement pattern in a mixed quantum state of the "universe", characterized by a universal topological network entanglement. As a concrete example we analyze the recently proposed model in which geometry emerges due to the condensation of 4-cycles in random regular bipartite graphs, driven by the combinatorial Ollivier-Ricci curvature. Using this model we show that the emergence of geometric order decreases the entanglement entropy of random configurations. The lowest geometric entanglement entropy is realized in four dimensions.

Author(s): S. P. Kish and T. C. Ralph

We study the problem of estimating the phase shift due to the general relativistic time dilation in the interference of photons using a nonlinear Mach-Zender interferometer setup. By introducing two nonlinear Kerr materials, one in the bottom and one in the top arm, we can measure the nonlinear phas...

[Phys. Rev. A 96, 041801(R)] Published Mon Oct 02, 2017

Authors: Andrei T. Patrascu

The discovery of the Higgs boson by the ATLAS and CMS collaborations allowed us to precisely determine its mass being 125.09 $\pm$ 0.24GeV. This value is intriguing as it lies at the frontier between the regions of stability and meta-stability of the standard model vacuum. It is known that the hierarchy problem can be interpreted in terms of the near criticality between the two phases. The coefficient of the Higgs bilinear in the scalar potential, $m^{2}$, is pushed by quantum corrections away from zero, towards the extremes of the interval $[-M^{2}_{Pl},M^{2}_{Pl}]$ where $M_{Pl}$ is the Planck mass. In this article, I show that demanding topological invariance for the renormalisation group allows us to extend the beta functions such that the particular value of the Higgs mass parameter observed in our universe regains naturalness. In holographic terms, invariance to changes of topology in the bulk is dual to a natural large hierarchy in the boundary quantum field theory. The demand of invariance to topology changes in the bulk appears to be strongly tied to the invariance of string theory to T-duality in the presence of H-fluxes.

Authors: Nicolas Gisin, Emmanuel Zambrini Cruzeiro

We consider a spin chain extending from Alice to Bob with next neighbors interactions, initially in its ground state. Assuming that Bob measures the last spin of the chain, the energy of the spin chain has to increase, at least on average, due to the measurement disturbance. Presumably, the energy is provided by Bob's measurement apparatus. Assuming now that, simultaneously to Bob's measurement, Alice measures the first spin, we show that either energy is not conserved, - implausible - or the projection postulate doesn't apply, and that there is signalling. An explicit measurement model shows that energy is conserved (as expected), but that the spin chain energy increase is not provided by the measurement apparatus(es), that the projection postulate is not always valid - illustrating the Wigner-Araki-Yanase (WAY) theorem - and that there is signalling, indeed. The signalling is due to the non-local interaction Hamiltonian. This raises the question of a suitable quantum information inspired model of such non-local Hamiltonians.

Bajlo, Darko (2017) The hidden arrow of electromagnetic radiation: unmasking advanced waves. UNSPECIFIED.


Mach’s principle asserts that the inertial mass of a body is related to the distribution of other distant bodies. This means that in the absence of other bodies, a single body has no mass. In this case, talking about motion is not possible, because the detection of motion is possible only relative to other bodies. But in physics we are faced with situations that are not fully Machian. As in the case of general theory of relativity where geodesics exist in the absence of any matter, the motion has meaning. Another example which is the main topic of our discussion, refers to Bohmian quantum mechanics, where the inertial mass of a single particle does not vanish, but is modified. We can call such situations in which motion or mass of a single particle has meaning, pseudo-Machian situations. In this paper, we use the Machian or pseudo-Machian considerations to clarify under what circumstances and how a Machian effect leads us to Bohmian quantum mechanics. Then, we shall get the Bohmian quantum potential and its higher order terms for the Klein-Gordon particle through Machian considerations, without using any quantum mechanical postulate or operator formalism.

Tsementzis, Dimitris and Halvorson, Hans (2016) Foundations and Philosophy. [Preprint]

Volume 3, Issue 4, pages 119-125

Andreas Schlatter [Show Biography]

Born in Zurich, Switzerland, Andreas Schlatter was educated at the Swiss Federal Institute of Technology in Zurich, where he studied mathematics. He got his PhD in 1994 with work in partial differential equations. He subsequently held a research position at Princeton University, where he did further work mainly on the Yang-Mills heat equation. In 1997 Andreas joined the Asset Management industry and pursued a distinguished career over twenty years, which brought him into the Executive Committee of one of the world’s large Asset Management firms. Today Andreas does consulting work and holds a number of independent board seats. Andreas has been doing research and published during his professional life, mainly in the area of Quantum Foundations and Relativity but also in Finance.

We assign to the radiation vacuum the role of a universal observer with a corresponding universal clock. By demanding that the thermal clock of a gravitationally accelerated observer in its local rest frame marches in step with the universal one, we derive relations between energy content and geometry of space-time.

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Volume 3, Issue 4, pages 100-118

Leonardo Chiatti [Show Biography]

Graduated in physics at Rome University “La Sapienza” in 1985, discussing a thesis on spin in stochastic mechanics under the guide of Marcello Cini. His interest focus on the conceptual foundations of quantum mechanics and their relation to areas as quantum dissipative phenomena, quantum cosmology and the spectrum of elementary particles. During ‘90s, he was involved in MQC Project aiming to produce superpositions of quantum states in mesoscopic systems (rf-SQUIDs). Successively, his interest enlarged to medical physics and currently he serves as physicist in chief at ASL Medical Physics Laboratory in Viterbo, Italy. Along the past decade he has been, in collaboration with Ignazio Licata, a proponent of de Sitter quantum cosmology. Together, they have proposed an "objective" view of quantum discontinuity as an "a-dynamic" aspect of interaction. This approach identifies the reduction of wave function with the physical phenomenon of the "quantum leap".

The customary description of radiation processes provided by Quantum Electrodynamics (QED) allows the quantitative derivation of many physical observables, in line with experiments. This extraordinary empirical success, however, leaves open the problem of the ontology of these processes. We identify these with the discontinuities of the evolution of the quantum state of the source, the so-called quantum jumps (QJ). Adopting a time-symmetrical view of the QJ borrowed from the transactional approach, the phenomena of radiation emission and absorption by an electron acquire an adynamic aspect, associated with their emergence from an atemporal background. The QJ activates the progressive generation of the electron timeline, along which its asymptotic state evolves. This causation process is of the formal type, and its dynamic “shadow” on the time domain is constituted by an interval during which the electron is self-interacting. Instead, in the absence of further interaction with external fields the asymptotic state is “on shell” i.e. not self-interacting. These ideas are used to constraint the value of the fine structure constant and of the cosmological constant, and to illustrate some less-known properties of electroweak decays.

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Authors: Richard J. Szabo

We examine certain nonassociative deformations of quantum mechanics and gravity in three dimensions related to the dynamics of electrons in uniform distributions of magnetic charge. We describe a quantitative framework for nonassociative quantum mechanics in this setting, which exhibits new effects compared to ordinary quantum mechanics with sourceless magnetic fields, and the extent to which these theoretical consequences may be experimentally testable. We relate this theory to noncommutative Jordanian quantum mechanics, and show that its underlying algebra can be obtained as a contraction of the alternative algebra of octonions. The uncontracted octonion algebra conjecturally describes a nonassociative deformation of three-dimensional quantum gravity induced by magnetic monopoles, which we propose is realised by a non-geometric Kaluza-Klein monopole background in M-theory.

Authors: Kevin Costello, Edward Witten, Masahito Yamazaki

Several years ago, it was proposed that the usual solutions of the Yang-Baxter equation associated to Lie groups can be deduced in a systematic way from four-dimensional gauge theory. In the present paper, we extend this picture, fill in many details, and present the arguments in a concrete and down-to-earth way. Many interesting effects, including the leading nontrivial contributions to the $R$-matrix, the operator product expansion of line operators, the framing anomaly, and the quantum deformation that leads from $\g[[z]]$ to the Yangian, are computed explicitly via Feynman diagrams. We explain how rational, trigonometric, and elliptic solutions of the Yang-Baxter equation arise in this framework, along with a generalization that is known as the dynamical Yang-Baxter equation.

Authors: M. Lahiri, A. Hochrainer, R. Lapkiewicz, G. B. Lemos, A. Zeilinger

Interference of two beams produced at separate biphoton sources was first observed more than two decades ago. The phenomenon, often called "induced coherence without induced emission", has recently gained attention after its applications to imaging, spectroscopy, and measuring biphoton correlations have been discovered. The sources used in the corresponding experiments are nonlinear crystals pumped by laser light. The use of a laser pump makes the occurrence of induced (stimulated) emission unavoidable and the effect of stimulated emission can be observed in the joint detection rate of the two beams. This fact raises the question whether the stimulated emission also lays a role in inducing the coherence. Here we investigate a case in which the crystals are pumped with a single-photon Fock state. We find that coherence is induced even though the possibility of stimulated emission is now fully ruled out. Furthermore, the joint detection rate of the two beams becomes ideally zero and does no longer change with the pump power. We illustrate our results by numerical simulations and by comparisons with experimental findings. Our results rule out any classical or semi-classical explanation of the phenomenon and also imply that similar experiments can be performed with fermions, for which stimulated emission is strictly forbidden.

Authors: Augusto Cesar Lobo

We address the relation between two apparently distinct problems: The quest for a deeper understanding of the nature of consciousness and the search for time and space as emergent structures in the quantum mechanical world. We also advance a toy-model proposal of emergence of time from a timeless unus mundus quantum-like space by using Aharonov's two state formalism of quantum mechanics. We further speculate on these issues within a quantum cognitive perspective with particular interest in two recent papers on this emerging field of science. One (Aerts et al) entails (as we argue) a panpsychist top-down approach to the problem of consciousness. The second paper (Blutner et al) proposes a quantum cognitive model for Jung's psychological type structure. We discuss these concepts and their relation with our main thesis, that time is a measure of individuality. One of our central motivations is to provide arguments that allows the mainstream physicist to take seriously a panpsychist worldview, a position that has been openly forwarded by many modern philosophers.

Authors: Gilles Brassard, Paul Raymond-Robichaud

We carry out a thought experiment in an imaginary world. Our world is both local and realistic, yet it violates a Bell inequality more than does quantum theory. This serves to debunk the myth that equates local realism with local hidden variables in the simplest possible manner. Along the way, we reinterpret the celebrated 1935 argument of Einstein, Podolsky and Rosen, and come to the conclusion that they were right in their questioning the completeness of quantum theory, provided one believes in a local-realistic universe. Throughout our journey, we strive to explain our views from first principles, without expecting mathematical sophistication nor specialized prior knowledge from the reader.

Authors: Simone Sturniolo

While historically many quantum mechanical simulations of molecular dynamics have relied on the Born-Oppenheimer approximation to separate electronic and nuclear behavior, recently a lot of interest has arisen towards quantum effects in nuclear dynamics as well, especially protons. Due to the computational difficulty of solving the Schr\"odinger equation in full, though, these effects are often treated with approximated, quasi-classical methods.

In this paper we present an extension to the Many Interacting Worlds approach to quantum mechanics developed using a kernel method to rebuild the probability density. This approach, at a difference with the approximation presented in the original paper, can be naturally extended to n-dimensional systems, making it a viable method for approximating both ground states and quantum evolution of physical systems. The behavior of the algorithm is studied in different potentials and numbers of dimensions and compared both to the original approach and to exact Schr\"odinger equation solutions whenever possible.

Authors: James Q. Quach, Maciej Lewenstein

We show that under the weak measurement scheme, the double-slit experiment can produce an interference pattern even when one of the slits is completely blocked. The initial and final states are corpuscular, whilst the intermediate states are wave-like, in that it exhibits an interference pattern. Remarkably, the interference pattern is measured to be vertically polarised, whilst simultaneously the individual photons are measured to be horizontally polarised. We call this the \textit{phantom slit} effect. The phantom slit is the dual of the quantum Cheshire cat.

Authors: D. Valente, F. Brito, R. Ferreira, T. Werlang

The work performed by a classical electromagnetic field on a quantum dipole is well known in quantum optics. The absorbed power linearly depends on the time derivative of the average dipole moment, in that case. The following problem, however, still lacks an answer: can the most elementary electromagnetic pulse, consisting of a single-photon state, perform work on a quantum dipole? As a matter of fact, the average quantum dipole moment exactly vanishes in such a scenario. In this paper, we present a method that positively answers to this question, by combining techniques from the fields of quantum machines and open quantum systems. Quantum work here is defined as the unitary contribution to the energy variation of the quantum dipole. We show that this quantum work corresponds to the energy spent by the photon pulse to dynamically Stark shift the dipole. The non-unitary contribution to the dipole energy is defined here as a generalized quantum heat. We show that this generalized quantum heat is the energy corresponding to out-of-equilibrium photon absorption and emission. Finally, we reveal connexions between the quantum work and the generalized quantum heat transferred by a single photon and those by a low-intensity coherent field.

Authors: Shu-Han Jiang, Zhen-Peng Xu, Hong-Yi Su, Arun Kumar Pati, Jing-Ling Chen

Hardy's paradox is an important all-versus-nothing proof of Bell's nonlocality. Hardy's original proof for two particles has been considered as "the simplest form of Bell's theorem" and "one of the strangest and most beautiful gems yet to be found in the extraordinary soil of quantum mechanics". Experimentally, a number of experiments has been carried out to confirm the paradox in two-particle systems. Theoretically, Hardy's paradox has been generalized from two-qubit to arbitrary $n$-qubit by Cereceda, who found that for the $n$-qubit GHZ state the maximal success probability is $[1+\cos\frac{\pi}{n-1}]/2^{n}$. Here we present the most general framework for $n$-particle Hardy's paradox, which includes Hardy's original one and Cereceda's extension as special cases. Remarkably, for any $n\ge 3$, there are always general Hardy's paradoxes (with the success probability $1/2^{n-1}$) that are stronger than the previous ones. An experimental proposal to observe the stronger paradox in the three-qubit system has also been presented. Furthermore, from the general Hardy's paradox we have constructed the most general Hardy's inequalities, which can detect Bell's nonlocality for more quantum states.

The idea that quantum computers can do things that regular ones cannot isn’t proven. But Google thinks it knows a problem only a quantum computer can solve
Publication date: Available online 28 September 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics
Author(s): Edward MacKinnon
The calculus that co-evolved with classical mechanics relied on definitions of functions and differentials that accommodated physical intuitions. In the early nineteenth century mathematicians began the rigorous reformulation of calculus and eventually succeeded in putting almost all of mathematics on a set-theoretic foundation. Physicists traditionally ignore this rigorous mathematics. Physicists often rely on a posteriori math, a practice of using physical considerations to determine mathematical formulations. This is illustrated by examples from classical and quantum physics. A justification of such practice stems from a consideration of the role of phenomenological theories in classical physics and effective theories in contemporary physics. This relates to the larger question of how physical theories should be interpreted.

Physicist Gil Lonzarich has sparked a revolution in the study of phase transitions driven by quantum fluctuations

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Author(s): J. K. Korbicz, E. A. Aguilar, P. Ćwikliński, and P. Horodecki

Measurement is of central interest in quantum mechanics as it provides the link between the quantum world and the world of everyday experience. One of the features of everyday experience is its robust, objective character, contrasting the delicate nature of quantum systems. Here we analyze in a comp...

[Phys. Rev. A 96, 032124] Published Thu Sep 28, 2017

Authors: Bruce Levinson

Humanity's efforts to transmute lead into gold have impelled civilizations. Our efforts to transmute human experience into objective laws have enjoyed similar success. Through thinkers such as Oliver Wendell Holmes, William James, Felix S. Cohen, Carol E. Cleland, Russell K. Standish and Christopher A. Fuchs we can see that a source of the difficulty in understanding phenomena via objective laws is that the law can best be understood as a quantum system, not a classical one. Law resembles a quantum system because maximal legal information is not complete and cannot be completed.

Barrett, Thomas William (2017) What Do Symmetries Tell Us About Structure? [Preprint]

Author(s): Xiang Zhan, Lei Xiao, Zhihao Bian, Kunkun Wang, Xingze Qiu, Barry C. Sanders, Wei Yi, and Peng Xue

We report the experimental detection of bulk topological invariants in nonunitary discrete-time quantum walks with single photons. The nonunitarity of the quantum dynamics is enforced by periodically performing partial measurements on the polarization of the walker photon, which effectively introduc...

[Phys. Rev. Lett. 119, 130501] Published Wed Sep 27, 2017

Author(s): M. Beau, J. Kiukas, I. L. Egusquiza, and A. del Campo

A system prepared in an unstable quantum state generally decays following an exponential law, as environmental decoherence is expected to prevent the decay products from recombining to reconstruct the initial state. Here we show the existence of deviations from exponential decay in open quantum syst...

[Phys. Rev. Lett. 119, 130401] Published Wed Sep 27, 2017

Authors: Augusto Cesar Lobo

We address the relation between two apparently distinct problems: The quest for a deeper understanding of the nature of consciousness and the search for time and space as emergent structures in the quantum mechanical world. We also advance a toy-model proposal of emergence of time from a timeless unus mundus quantum-like space by using Aharonov's two state formalism of quantum mechanics. We further speculate on these issues within a quantum cognitive perspective with particular interest in two recent papers on this emerging field of science. One (Aerts et al) entails (as we argue) a panpsychist top-down approach to the problem of consciousness. The second paper (Blutner et al) proposes a quantum cognitive model for Jung's psychological type structure. We discuss these concepts and their relation with our main thesis, that time is a measure of individuality. One of our central motivations is to provide arguments that allows the mainstream physicist to take seriously a panpsychist worldview, a position that has been openly forwarded by many modern philosophers.

Authors: Danko Georgiev, Eliahu Cohen

Feynman's sum-over-histories formulation of quantum mechanics has been considered a useful calculational tool in which virtual Feynman histories entering into a quantum superposition cannot be individually measured. Here we show that sequential weak values inferred by weak measurements allow direct experimental probing of individual virtual Feynman histories thereby revealing the exact nature of quantum interference of superposed histories. In view of the existing controversy over the meaning and interpretation of weak values, our analysis demonstrates that sequential weak values of quantum histories (multi-time projection operators) are not arbitrary, but reflect true physical properties of the quantum physical system under study. If weak values are interpreted for a complete set of orthogonal quantum histories, the total sum of weak values is unity and the analysis agrees with the standard quantum mechanical picture.

Authors: Yakir Aharonov, Eliahu Cohen, Avishy Carmi, Avshalom C. Elitzur

Some predictions regarding pre- and post-selected particles are far-reaching, thereby requiring validation with standard quantum measurements in addition to the customary weak measurements used so far, as well as other advanced techniques. Following earlier papers, we continue this research program with two thought experiments. An excited atom traverses a Mach-Zehnder interferometer (MZI) under a special combination of pre- and post-selection. In the first experiment, photons emitted by the superposed atom, after being hit by two laser beams, are individually counted. Despite the interaction having definitely taken place, as revealed by the atom becoming ground, the numbers of photons emitted from each arm of the MZI are predicted, at the ensemble level, to be different from those expected with standard stimulated emission of a pre-selected-only atom. In the second experiment, the atom spontaneously emits a photon while still in the MZI. This photon later serves as a strong measurement of the atom's energy upon hitting a photographic plate. The experiment is repeated to enable an interference effect of the emitted photons. Surprisingly, the latter gives the appearance that the photons have been emitted by the atom from a position much farther from the two MZI arms L and R, as if in a "phantom arm" R'. Nevertheless, their time of arrival is similar to that of photons coming from L and R. These experiments also emphasize the key role of negative weak values of atoms under pre- and post-selection. The novel verification methods resemble weak measurements in some aspects, yet result from an unambiguous atomic transitions verified by the detected photons.

Ultrafast creation of large Schrödinger cat states of an atom

Nature Communications, Published online: 26 September 2017; doi:10.1038/s41467-017-00682-6

Generation of mesoscopic quantum superpositions requires both reliable coherent control and isolation from the environment. Here, the authors succeed in creating a variety of cat states of a single trapped atom, mapping spin superpositions into spatial superpositions using ultrafast laser pulses.

Schiemer, Georg and Wigglesworth, John (2017) The Structuralist Thesis Reconsidered. The British Journal for the Philosophy of Science.
Techniques could lead to better quantum-information networks

Authors: Gianluca Calcagni

Getting signatures of quantum gravity is one of the topical lines of research in modern theoretical physics and cosmology. This short review faces this challenge under a novel perspective. Instead of separating quantum-gravity effects of a specific model between UV and IR regimes, we consider a general feature, possibly common to many frameworks, where all scales are affected and spacetime geometry is characterized by a complex critical exponent. This leaves a log-oscillating modulation pattern in the cosmic microwave background spectrum and gives a unique opportunity, illustrated with the example of a multi-fractional theory, to test quantum gravities at cosmological scales.

Jabs, Arthur (2014) An interpretation of the formalism of quantum mechanics in terms of realism. arXiv, The British Journal for the Philosophy of Science, 43. pp. 405-421.
North, Jill (2017) A New Approach to the Relational-Substantival Debate. [Preprint]
Jabs, Arthur (2017) A conjecture concerning determinism, reduction, and measurement in quantum mechanics. arXiv. pp. 1-21.
Jabs, Arthur (2017) Quantum mechanics in terms of realism. arXiv. pp. 1-100.
Publication date: August 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, Volume 59
Author(s): Doreen Fraser
The application of analytic continuation in quantum field theory (QFT) is juxtaposed to T-duality and mirror symmetry in string theory. Analytic continuation—a mathematical transformation that takes the time variable t to negative imaginary time—it—was initially used as a mathematical technique for solving perturbative Feynman diagrams, and was subsequently the basis for the Euclidean approaches within mainstream QFT (e.g., Wilsonian renormalization group methods, lattice gauge theories) and the Euclidean field theory program for rigorously constructing non-perturbative models of interacting QFTs. A crucial difference between theories related by duality transformations and those related by analytic continuation is that the former are judged to be physically equivalent while the latter are regarded as physically inequivalent. There are other similarities between the two cases that make comparing and contrasting them a useful exercise for clarifying the type of argument that is needed to support the conclusion that dual theories are physically equivalent. In particular, T-duality and analytic continuation in QFT share the criterion for predictive equivalence that two theories agree on the complete set of expectation values and the mass spectra and the criterion for formal equivalence that there is a “translation manual” between the physically significant algebras of observables and sets of states in the two theories. The analytic continuation case study illustrates how predictive and formal equivalence are compatible with physical inequivalence, but not in the manner of standard underdetermination cases. Arguments for the physical equivalence of dual theories must cite considerations beyond predictive and formal equivalence. The analytic continuation case study is an instance of the strategy of developing a physical theory by extending the formal or mathematical equivalence with another physical theory as far as possible. That this strategy has resulted in developments in pure mathematics as well as theoretical physics is another feature that this case study has in common with dualities in string theory.

Publication date: August 2017
Source:Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics, Volume 59
Author(s): Joseph Polchinski
Duality, the equivalence between seemingly distinct quantum systems, is a curious property that has been known for at least three quarters of a century. In the past two decades it has played a central role in mapping out the structure of theoretical physics. I discuss the unexpected connections that have been revealed among quantum field theories and string theories. Written for a special issue of Studies in History and Philosophy of Modern Physics.