We design and implement a quantum laboratory to experimentally observe and study dynamical processes of quantum field theories. Our approach encodes the field theory as an Ising model, which is then solved by a quantum annealer. As a proof-of-concept, we encode a scalar field theory and measure the probability for it to tunnel from the false to the true vacuum for various tunnelling times, vacuum displacements and potential profiles. The results are in accord with those predicted theoretically, showing that a quantum annealer is a genuine quantum system that can be used as a quantum laboratory. This is the first time it has been possible to experimentally measure instanton processes in a freely chosen quantum field theory. This novel and flexible method to study the dynamics of quantum systems can be applied to any field theory of interest. Experimental measurements of the dynamical behaviour of field theories are independent of theoretical calculations and can be used to infer their properties without being limited by the availability of suitable perturbative or nonperturbative computational methods. In the near future, measurements in such a quantum laboratory could therefore be used to improve theoretical and computational methods conceptually and may enable the measurement and detailed study of previously unobserved quantum phenomena.

Authors: Carlo Roselli, Bruno Raffaele Stella

This paper aims to falsify the hypothesis that the observer’s consciousness is necessary for quantum measurement. To achieve our target, we propose a variation of the Schroedinger’s cat thought experiment called “DAP”, short for “Dead-Alive Physicist”, in which a human being replaces the cat. This strategy enables us to logically disprove the consistency of the above hypothesis and to oblige its supporters either to be trapped in solipsism or to rely on an alternative interpretation of quantum mechanics in which the role of the conscious observer has to be reviewed. Our analysis hence provides support to clarify the relationship between the observer the objects of her/his experimental observation; this and a few other implications are discussed in the fourth section and in the conclusions.

Authors: Philippe Grangier

In standard quantum mechanics (QM), a state vector $| \psi \rangle$ may belong to infinitely many different orthogonal bases, as soon as the dimension $N$ of the Hilbert space is at least three. On the other hand, a complete physical observable $A$ (with no degeneracy left) is associated with a $N$-dimensional orthogonal basis of eigenvectors. In an idealized case, measuring $A$ again and again will give repeatedly the same result, with the same eigenvalue. Let us call this repeatable result a modality $\mu$, and the corresponding eigenstate $| \psi \rangle$. A question is then: does $| \psi \rangle$ give a complete description of $\mu$ ?

The answer is obviously no, since $| \psi \rangle$ does not specify the full observable $A$ that allowed us to obtain $\mu$; hence the physical description given by $| \psi \rangle$ is incomplete, as claimed by Einstein, Podolsky and Rosen in their famous article in 1935. Here we want to spell out this provocative statement, and in particular to answer the questions: if $| \psi \rangle$ is an incomplete description of $\mu$, what does it describe ? is it possible to obtain a complete description, maybe algebraic ? Our conclusion is that the incompleteness of standard QM is due to its attempt to describe systems without contexts, whereas both are always required; they can be separated only outside the measurement periods.

Authors: Andrea Oldofredi, Cristian Lopez

Harrigan and Spekkens (2010) provided a categorization of quantum ontological models classifying them as $\psi$-ontic or $\psi$-epistemic if the quantum state describes respectively either a physical reality or mere observers’ knowledge. Moreover, they claimed that Einstein – who was a supporter of the statistical interpretation of quantum mechanics – endorsed an epistemic view of $\psi$. In this essay we critically assess such a classification and some of its consequences by proposing a two-fold argumentation. Firstly, we show that Harrigan and Spekkens’ categorization implicitly assumes that a complete description of a quantum system (its ontic state, $\lambda$) only concerns single, individual systems instantiating absolute, intrinsic properties. Secondly, we argue that such assumptions conflict with some current interpretations of quantum mechanics, which employ different ontic states as a complete description of quantum systems. In particular, we will show that, since in the statistical interpretation ontic states describe ensembles rather than individuals, such a view cannot be considered psi-epistemic. As a consequence, the authors misinterpreted Einstein’s view concerning the nature of the quantum state. Next, we will focus on Relationalist Quantum Mechanics and Perspectival Quantum Mechanics, which in virtue of their relational and perspectival metaphysics employ ontic states lambda dealing with relational properties. We conclude that Harrigan and Spekkens’ categorization is too narrow and entails an inadequate classification of the mentioned interpretations of quantum theory. Hence, any satisfactory classification of quantum ontological models ought to take into account the variations of $\lambda$ across different interpretations of quantum mechanics.

Publication date: Available online 10 June 2020

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

Author(s): Marco Giovanelli

Authors: Marius Oltean, Hossein Bazrafshan Moghaddam, Richard J. Epp

Quasilocal definitions of stress-energy-momentum—that is, in the form of boundary densities (in lieu of local volume densities)—have proven generally very useful in formulating and applying conservation laws in general relativity. In this essay, we take a first basic look into applying these to cosmology, specifically using the Brown-York quasilocal stress-energy-momentum tensor for matter and gravity combined. We compute this tensor and present some simple results for a flat FLRW spacetime with a perfect fluid matter source.

Authors: J.C. Castro-Palacio, P. Fernandez de Cordoba, J.M. Isidro

We present a simple quantum-mechanical estimate of the cosmological constant of a Newtonian Universe. We first mimic the dynamics of a Newtonian spacetime by means of a nonrelativistic quantum mechanics for the matter contents of the Universe (baryonic and dark) within a fixed (i.e., nondynamical) Euclidean spacetime. Then we identify an operator that plays, on the matter states, a role analogous to that played by the cosmological constant. Finally we prove that there exists a quantum state for the matter fields, in which the above mentioned operator has an expectation value equal to the cosmological constant of the given Newtonian Universe.

Authors: Lorenzo Bordin, Edmund J. Copeland, Antonio Padilla

We revisit the constraints on scalar tensor theories of modified gravity following the purge of GW170817. We pay particular attention to dynamical loopholes where the anomalous speed of propagation of the gravitational wave can vanish on-shell, when we impose the dynamical field equations. By working in the effective field theory formalism we are able to improve on previous analyses, scanning a much wider class of theories, including Beyond Horndeski and DHOST. Furthermore, the formalism is well adapted to consider the effect of inhomogeneous perturbations, where we explicitly take into account the fact that the galactic overdensities are pressureless to leading order.

Authors: Sung-Sik Lee

We construct a model of quantum gravity in which dimension, topology and geometry of spacetime are dynamical. The microscopic degree of freedom is a real rectangular matrix whose rows label internal flavours, and columns label spatial sites. In the limit that the size of the matrix is large, the sites can collectively form a spatial manifold. The manifold is determined from the pattern of entanglement present across local Hilbert spaces associated with column vectors of the matrix. With no structure of manifold fixed in the background, the spacetime gauge symmetry is generalized to a group that includes diffeomorphism in arbitrary dimensions. The momentum and Hamiltonian that generate the generalized diffeomorphism obey a first-class constraint algebra at the quantum level. In the classical limit, the constraint algebra of the general relativity is reproduced as a special case. The first-class nature of the algebra allows one to express the projection of a quantum state of the matrix to a gauge-invariant state as a path integration of dynamical variables that describe collective fluctuations of the matrix. The collective variables describe dynamics of emergent spacetime, where multi-fingered times arise as Lagrangian multipliers that enforce the gauge constraints. If the quantum state has a local structure of entanglement, a smooth spacetime with well-defined dimension, topology, signature and geometry emerges at the saddle-point, and the spin two mode that determines the geometry can be identified. We find a saddle-point solution that describes a series of (3+1)-dimensional de Sitter-like spacetimes with the Lorentzian signature bridged by Euclidean spaces in between. Fluctuations of the collective variables are described by bi-local fields that propagate in the spacetime set up by the saddle-point solution.

Authors: R. Casadio, F. Scardigli

The Generalized Uncertainty Principle (GUP) has been directly applied to the motion of (macroscopic) test bodies on a given space-time in order to compute corrections to the classical orbits predicted in Newtonian Mechanics or General Relativity. These corrections generically violate the Equivalence Principle. The GUP has also been indirectly applied to the gravitational source by relating the GUP modified Hawking temperature to a deformation of the background metric. Such a deformed background metric determines new geodesic motions without violating the Equivalence Principle. We point out here that the two effects are mutually exclusive when compared with experimental bounds. Moreover, the former stems from modified Poisson brackets obtained from a wrong classical limit of the deformed canonical commutators.

Ferreirós, José (1995) “What Fermented in Me for Years”: Cantor’s discovery of transfinite numbers. Historia Mathematica, 22. pp. 33-42. ISSN 03150860

Ferreirós, José (2004) The Motives behind Cantor’s Set Theory – Physical, Biological, and Philosophical Questions. Science in Context, 17 (1). pp. 49-83.

Ferreirós, José (2017) Wigner’s ‘Unreasonable Effectiveness’ in Context. Mathematical Intelligencer, 39 (2). pp. 64-71. ISSN 1866-7414

Author(s): Yi-Tao Wang, Zhi-Peng Li, Shang Yu, Zhi-Jin Ke, Wei Liu, Yu Meng, Yuan-Ze Yang, Jian-Shun Tang, Chuan-Feng Li, and Guang-Can Guo

Comprehensive study on parity-time (PT) symmetric systems demonstrates the novel properties and innovative application of non-Hermitian physics in recent years. In the quantum regime, PT symmetric physics exhibits unique quantum dynamical behaviors such as spontaneous state-distinguishability oscill…

[Phys. Rev. Lett. 124, 230402] Published Thu Jun 11, 2020

De Haro, Sebastian (2020) Spacetime and Physical Equivalence. In: UNSPECIFIED.

Romano, Davide (2020) Multi-field and Bohm’s theory. [Preprint]

Nature Physics, Published online: 11 June 2020; doi:10.1038/s41567-020-0940-7

Since the 1950s, international cooperation has been the driving force behind fusion research. Here, we discuss how the International Atomic Energy Agency has shaped the field and the events that have produced fusion’s global signature partnership.

Abstract

Evaluating counterfactuals in worlds with deterministic laws poses a puzzle. In a wide array of cases, it does not seem plausible that if a non-actual event were to occur that either the past would be different or that the laws would be different. But it’s also difficult to see how we can avoid this result. Some philosophers have argued that we can avoid this dilemma by allowing that a proposition can be a law even though it has violations. On this view, for the relevant cases, the past and the laws would still hold, but the laws would have a violation. In this paper, I raise a problem for the claim that the laws and the past are preserved for all of the relevant counterfactual antecedents. I further argue that this problem undermines motivating the possibility of violations on the grounds that they allow us to hold that the past and the laws are typically counterfactually preserved, even if they are not always preserved.

Chen, Eddy Keming (2020) From Time Asymmetry to Quantum Entanglement: The Humean Unification. [Preprint]

Author(s): Zhen-Peng Xu, Jing-Ling Chen, and Otfried Gühne

A central result in the foundations of quantum mechanics is the Kochen-Specker theorem. In short, it states that quantum mechanics cannot be reconciled with classical models that are noncontextual for ideal measurements. The first explicit derivation by Kochen and Specker was rather complex, but con…

[Phys. Rev. Lett. 124, 230401] Published Tue Jun 09, 2020