Abstract

The principle of the common cause claims that if an improbable coincidence has occurred, there must exist a common cause. This is generally taken to mean that positive correlations between non-causally related events should disappear when conditioning on the action of some underlying common cause. The extended interpretation of the principle, by contrast, urges that common causes should be called for in order to explain positive deviations between the estimated correlation of two events and the expected value of their correlation. The aim of this paper is to provide the extended reading of the principle with a general probabilistic model, capturing the simultaneous action of a system of multiple common causes. To this end, two distinct models are elaborated, and the necessary and sufficient conditions for their existence are determined.

Authors: Thomas C. Bachlechner, Matthew Kleban

The phase of the wave function of charged matter is sensitive to the value of the electric potential, even when the matter never enters any region with non-vanishing electromagnetic fields. Despite its fundamental character, this archetypal electric Aharonov-Bohm effect has evidently never been observed. We propose an experiment to detect the electric potential through its coupling to the superconducting order parameter. A potential difference between two superconductors will induce a relative phase shift that is observable via the DC Josephson effect even when no electromagnetic fields ever act on the superconductors, and even if the potential difference is later reduced to zero. This is a type of electromagnetic memory effect, and would directly demonstrate the physical significance of the electric potential.

Authors: David Glick, Florian J. Boge

Tim Maudlin has claimed that EPR’s Reality Criterion is analytically true. We argue that it is not. Moreover, one may be a subjectivist about quantum probabilities without giving up on objective physical reality. Thus, would-be detractors must reject QBism and other epistemic approaches to quantum theory on other grounds.

Authors: A. Ferreri, M. Domina, L. Rizzuto, R. Passante

We investigate the spontaneous emission of one atom placed near an oscillating perfectly reflecting plate. We consider the atom modeled as a two-level system, interacting with the quantum electromagnetic field in the vacuum state, in the presence of an oscillating mirror. We suppose that the plate oscillates adiabatically, so that the time-dependence of the interaction Hamiltonian is entirely enclosed in the time-dependent mode functions, satisfying the boundary conditions at the plate surface, at any given time. Using time-dependent perturbation theory, we evaluate the transition rate to the ground-state of the atom, and show that it depends on the time-dependent atom-plate distance. We also show that the presence of the oscillating mirror significantly affects the physical features of the spontaneous emission by the atom, in particular the spectrum of the emitted radiation. Specifically, we find the appearance of two lateral peaks in the spectrum, not present in the case of a static mirror, due to the presence of the modulated environment. The two lateral peaks are separated from the central peak by the modulation frequency, and we discuss the possibility to observe them with actual experimental setups. Our results indicate that a dynamical (i.e. time-modulated) environment can give new possibilities to control and manipulate also other radiative processes of atoms or molecules nearby, for example the resonance energy transfer between atoms or molecules and their cooperative decay.

Authors: Adán Cabello

The totalitarian principle establishes that `anything not forbidden is compulsory’. The problem of quantum correlations is explaining what selects the set of quantum correlations for a Bell and Kochen-Specker (KS) contextuality scenario. Here, we show that two assumptions and a version of the totalitarian principle lead to the quantum correlations. The assumptions are that there is a non-empty set of correlations for any KS contextuality scenario and a statistically independent realisation of any two KS experiments. The version of the totalitarian principle says that any correlation not forbidden by these assumptions can be produced. This paper contains a short version of the proof [presented in {\em Phys. Rev. A} \textbf{100}, 032120 (2019)] and explores some implications of the result.

This article is part of the theme issue `Contextuality and probability in quantum mechanics and beyond’.

Authors: Ognyan Oreshkov

It has been shown that it is theoretically possible for there to exist higher-order quantum processes in which the operations performed by separate parties cannot be ascribed a definite causal order. Some of these processes are believed to have a physical realization in standard quantum mechanics via coherent control of the times of the operations. A prominent example is the quantum SWITCH, which was recently demonstrated experimentally. However, the interpretation of such experiments as realizations of a process with indefinite causal structure as opposed to some form of simulation of such a process has remained controversial. Where exactly are the local operations of the parties in such an experiment? On what spaces do they act given that their times are indefinite? Can we probe them directly rather than assume what they ought to be based on heuristic considerations? How can we reconcile the claim that these operations really take place, each once as required, with the fact that the structure of the presumed process implies that they cannot be part of any acyclic circuit? Here, I offer a precise answer to these questions: the input and output systems of the operations in such a process are generally nontrivial subsystems of Hilbert spaces that are tensor products of Hilbert spaces associated with systems at different times—a fact that is directly experimentally verifiable. With respect to these time-delocalized subsystems, the structure of the process is one of a circuit with a causal cycle. I also identify a whole class of isometric processes, of which the quantum SWITCH is a special case, that admit a physical realization on time-delocalized subsystems. These results unveil a novel structure within quantum mechanics, which may have important implications for physics and information processing.

Authors: Andrzej Trautman, Donald Salisbury

The text presented here and revised by the authors is based on the original oral history interview by Donald Salisbury with Andrzej Trautman recorded in Warsaw on June 24 and June 28, 2016.

Publication date: Available online 25 September 2019

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

Author(s): Allen Stairs

Authors: Robert J. Scherrer

In the Ijjas-Steinhardt cyclic model, the universe passes through phases dominated by radiation, matter, and a dark energy scalar field, with the value of the scale factor increasing with each cycle. Since each cycle terminates in a finite time, it is straightforward to calculate the fraction of time that the universe spends in a state for which the matter and dark energy densities have comparable magnitudes; when this fraction is large, it can be taken as a solution of the coincidence problem. This solution of the coincidence problem requires a relatively short lifetime for each cycle, but unlike in the case of phantom models, there is no fixed upper bound on this lifetime. However, scalar field models satisfying the Swampland conjectures yield sufficiently short lifetimes to provide a satisfactory resolution of the coincidence problem.

Authors: Hareesh T, P.B. Krishna, Titus K Mathew

The emergence of cosmic space as cosmic time progresses is an exciting idea advanced by Padmanabhan to explain the accelerated expansion of the universe. The generalization of Padmanabhan’s conjecture to the non-flat universe has resulted in scepticism about the choice of volume such that the law of emergence can not be appropriately formulated if one uses proper invariant volume. The deep connection between the first law of thermodynamics and the law of emergence \cite{mahith}, motivate us to explore the status of the first law in a non-flat universe when one uses proper invariant volume. We have shown that the first law of thermodynamics, $dE = TdS +WdV$ cannot be formulated properly for a non-flat universe using proper invariant volume. We have also investigated the status of the first law of the form $-dE = TdS$ in a non-flat universe. We have shown that the energy change dE within the horizon and the outward energy flux are not equivalent to each other in a non-flat universe when we use the proper invariant volume. We have further shown that the consistency between the above two forms of the first law claimed in Ref. \cite{caiakb} will hold only with the use of the areal volume of the horizon. Thus, a consistent formulation of the above two forms of the first law of thermodynamics demands the use of areal volume.

Authors: Alek Bedroya, Cumrun Vafa

In this paper, we propose a new Swampland condition, the Trans-Planckian Censorship Conjecture (TCC), based on the idea that in a consistent quantum theory of gravity sub-Planckian quantum fluctuations should remain quantum and never become larger than the Hubble horizon and freeze in an expanding universe. Applied to the case of scalar fields, it leads to conditions that are similar to the refined dS Swampland conjecture. For large field ranges, TCC is stronger than the dS Swampland conjecture but it is weaker for small field ranges. In particular for asymptotic regions of field space, TCC leads to a bound $|V’|\geq {2\over \sqrt{(d-1)(d-2)}}V$, which is consistent with all known cases in string theory. Like the dS Swampland conjecture, the TCC forbids long-lived meta-stable dS spaces, but it does allow sufficiently short-lived ones.

Eder, Anna-Maria A. (2019) Evidential Probabilities and Credences. The British Journal for the Philosophy of Science. ISSN 1464-3537

Author(s): Guglielmo Mazzola, Pauline J. Ollitrault, Panagiotis Kl. Barkoutsos, and Ivano Tavernelli

We introduce a quantum Monte Carlo inspired reweighting scheme to accurately compute energies from optimally short quantum circuits. This effectively hybrid quantum-classical approach features both entanglement provided by a short quantum circuit, and the presence of an effective nonunitary operator…

[Phys. Rev. Lett. 123, 130501] Published Fri Sep 27, 2019

Abstract

We review several no-go theorems attributed to Gisin and Hardy, Conway and Kochen purporting the impossibility of Lorentz-invariant deterministic hidden-variable model for explaining quantum nonlocality. Those theorems claim that the only known solution to escape the conclusions is either to accept a preferred reference frame or to abandon the hidden-variable program altogether. Here we present a different alternative based on a foliation dependent framework adapted to deterministic hidden variables. We analyse the impact of such an approach on Bohmian mechanics and show that retrocausation (that is future influencing the past) necessarily comes out without time-loop paradox.

Nature Physics, Published online: 23 September 2019; doi:10.1038/s41567-019-0663-9

Matter-wave interference experiments demonstrate quantum superposition of molecules consisting of up to 2,000 atoms—the heaviest objects to show this quantum behaviour to date. This provides a bound on potential modifications to quantum mechanics.

The ‘Cosmological Constant Problem’ (CCP) has historically been understood as describing a conflict between cosmological observations in the framework of general relativity (GR) and theoretical predictions from quantum field theory (QFT), which a future theory of quantum gravity ought to resolve. I argue that this view of the CCP is best understood in terms of a bet about future physics made on the basis of particular interpretational choices in GR and QFT respectively. Crucially, each of these choices must be taken as itself grounded in the success of the respective theory for this bet to be justified.