# Weekly Papers on Quantum Foundations (21)

Quantum imprints of gravitational shockwaves. (arXiv:2105.09337v1 [hep-th])

Gravitational shockwaves are simple exact solutions of Einstein equations representing the fields of ultrarelativistic sources and idealized gravitational waves (shocks). Historically, much work has focused on shockwaves in the context of possible black hole formation in high energy particle collisions, yet they remain at the forefront of research even today. Representing hard modes in the bulk, shocks give rise to the gravitational memory effect at the classical level and implant supertranslation (BMS) hair onto a classical spacetime at the quantum level. The aim of this paper is to further our understanding of the `information content’ of such supertranslations. Namely, we show that, contrary to the several claims in the literature, a gravitational shockwave does leave a quantum imprint on the vacuum state of a test quantum field and that this imprint is accessible to local observers carrying Unruh–DeWitt (UDW) detectors in this spacetime.

Any Physical Theory of Nature Must Be Boundlessly Multipartite Nonlocal. (arXiv:2105.09380v1 [quant-ph])

We introduce the class of Genuinely Local Operation and Shared Randomness (LOSR) Multipartite Nonlocal correlations, that is, correlations between N parties that cannot be obtained from unlimited shared randomness supplemented by any composition of (N-1)-shared causal Generalized-Probabilistic-Theory (GPT) resources. We then show that noisy N-partite GHZ quantum states as well as the 3-partite W quantum state can produce such correlations. This proves, if the operational predictions of quantum theory are correct, that Nature’s nonlocality must be boundlessly multipartite in any causal GPT. We develop a computational method which certifies that a noisy N=3 GHZ quantum state with fidelity 85 percent satisfies this property, making an experimental demonstration of our results within reach. We motivate our definition and contrast it with preexisting notions of genuine multipartite nonlocality. This work extends a more compact parallel letter on the same subject and provides all the required technical proofs.

No Bipartite-Nonlocal Causal Theory Can Explain Nature’s Correlations. (arXiv:2105.09381v1 [quant-ph])

We show that some tripartite quantum correlations are inexplicable by any causal theory involving bipartite nonclassical common causes and unlimited shared randomness. This constitutes a device-independent proof that Nature’s nonlocality is fundamentally at least tripartite in every conceivable physical theory – no matter how exotic. To formalize this claim we are compelled to substitute Svetlichny’s historical definition of genuine tripartite nonlocality with a novel theory-agnostic definition tied to the framework of Local Operations and Shared Randomness (LOSR). An extended paper accompanying this work generalizes these concepts to any number of parties, providing experimentally amenable device-independent inequality constraints along with quantum correlations violating them, thereby certifying that Nature’s nonlocality must be boundlessly multipartite.

No causal order and topological phases. (arXiv:2105.09795v1 [quant-ph])

We consider a topological Hamiltonian and establish a correspondence between its eigenstates and the resource for a causal order game introduced in Ref. \cite{brukner}, known as {\it process matrix}. We show that quantum correlations generated in the quantum many-body energy eigenstates of the model can mimic the statistics that can be obtained by exploiting different quantum measurements on the process matrix of the game. This provides an interpretation of the expectation values of the observables computed for the quantum many-body states in terms of success probabilities of the game. As a result, we show that the ground state of the model can be related to the optimal strategy of the causal order game. Along with this, we show that a correspondence between the considered topological quantum Hamiltonian and the causal order game can also be made by relating the behavior of topological order parameters characterizing different phases of the model with the different regions of the causal order game.

PT symmetry and the evolution speed in open quantum systems. (arXiv:2105.09853v1 [quant-ph])

The dynamics of an open quantum system with balanced gain and loss is not described by a PT-symmetric Hamiltonian but rather by Lindblad operators. Nevertheless the phenomenon of PT-symmetry breaking and the impact of exceptional points can be observed in the Lindbladean dynamics. Here we briefly review the development of PT symmetry in quantum mechanics, and the characterisation of PT-symmetry breaking in open quantum systems in terms of the behaviour of the speed of evolution of the state.

The geometrical interpretation of the photon position operator. (arXiv:2104.04351v4 [quant-ph] UPDATED)

It is shown that the photon position operator $\hat{\vec{X}}$ with commuting components can be written in the momentum representation as $\hat{\vec{X}}=i \hat{\vec{D}}$, where $\hat{\vec{D}}$ is a flat connection in the tangent bundle $T(\mathbb{R}^3 \setminus \{ (0,0,k_3) \in \mathbb{R}^3 : k_3 \geq 0\})$ over $\mathbb{R}^3 \setminus \{ (0,0,k_3) \in \mathbb{R}^3 : k_3 \geq 0\}$ equipped with the Cartesian structure. Moreover, $\hat{\vec{D}}$ is such that the tangent $2$-planes orthogonal to the momentum are parallelly propagated with respect to $\hat{\vec{D}}$ and, also, $\hat{\vec{D}}$ is an anti-Hermitian operator with respect to the scalar product $\langle \mathbf{\Psi} | \hat{H}^{-2s} |\mathbf{\Phi} \rangle$. The eigenfunctions $\mathbf{\Psi}_{\vec{X}} (\vec{x})$ of the position operator $\hat{\vec{X}}$ are found.

Addendum to “Strong cosmic censorship: The nonlinear story”. (arXiv:2012.08413v3 [gr-qc] UPDATED)

We clarify a number of issues that arise when extending the analysis of Strong Cosmic Censorship (SCC) to perturbations of highly charged Reissner-Nordstr\”{o}m de Sitter (RNdS) spacetimes. The linear stability of the Cauchy horizon can be determined from the spectral gap of quasinormal modes, thus giving a clear idea of the ranges of parameters that are likely to lead to SCC violations for infinitesimally small perturbations. However, the situation becomes much more subtle once nonlinear backreaction is taken into account. These subtleties have created a considerable amount of confusion in the literature regarding the conclusions one is able to derive about SCC from the available numerical simulations. Here we present new numerical results concerning charged self-gravitating scalar fields in spherical symmetry, correct some previous claims concerning the neutral case, and argue that the existing numerical codes are insufficient to draw conclusions about the potential failure of SCC for near extremal RNdS black hole spacetimes.

Constitutive elements in science beyond physics: the case of the Hardy–Weinberg principle

Luchetti, Michele (2018) Constitutive elements in science beyond physics: the case of the Hardy–Weinberg principle. [Preprint]

Is the photon really a particle?

Klevgard, Paul A. (2021) Is the photon really a particle? Optik International Journal for Light and Electron Optics, 237. ISSN 0030-4026

The Never-Ending Dance of Philosophy and Physics

Huggett, Nick and Norton, Joshua (2018) The Never-Ending Dance of Philosophy and Physics. UNSPECIFIED.

From successful measurement to the birth of a law: Disentangling coordination in Ohm’s scientific practice

Luchetti, Michele (2020) From successful measurement to the birth of a law: Disentangling coordination in Ohm’s scientific practice. [Preprint]

Composing Spacetime

Baron, Sam and Le Bihan, Baptiste (2021) Composing Spacetime. [Preprint]

Dutch Book against Lewis

Abstract

According to the PCCP thesis, the probability of a conditional A → C is the conditional probability P(C|A). This claim is undermined by Lewis’ triviality results, which purport to show that apart from trivial cases, PCCP is not true. In the present article we show that the only rational, “Dutch Book-resistant” extension of the agent’s beliefs concerning non-conditional sentences A and C to the conditional A → C is by assuming that P(A → C) = P(C|A) (i.e., in accord with PCCP). In other cases a diachronic Dutch Book against the agent can be constructed. There is a tension between our findings and Lewis’ results, which needs to be explained. Therefore, we present a probability space which corresponds in a natural way to the diachronic Dutch Book—and which allows the conditional A → C to be interpreted as an event in a mathematically sound way. It also allows to formalize the notion of conditionalizing A → C on ¬C which plays a crucial role in Lewis’ proof. Our conclusion is that Lewis’ proof is circular, so it cannot be considered to be a sound argument against PCCP.

Gravitational Decoherence and the Possibility of Its Interferometric Detection

Author(s): L. Asprea, A. Bassi, H. Ulbricht, and G. Gasbarri

We present a general master equation describing the quantum dynamics of a scalar bosonic field interacting with an external weak and stochastic gravitational field. The dynamics predicts decoherence both in position and in energy momentum. We show how the master equation reproduces, thus generalizin…

[Phys. Rev. Lett. 126, 200403] Published Wed May 19, 2021

Saving Proof from Paradox: Gödel’s Paradox and the Inconsistency of Informal Mathematics

Tanswell, Fenner Stanley (2016) Saving Proof from Paradox: Gödel’s Paradox and the Inconsistency of Informal Mathematics. [Preprint]

What’s the Point of Authors?

habgood-coote, joshua (2019) What’s the Point of Authors? [Preprint]

Nothing to Come in a relativistic setting

Dorato, Mauro and Hoefer, Carl (2021) Nothing to Come in a relativistic setting. [Preprint]

Renormalized Mutual Information for Artificial Scientific Discovery

Author(s): Leopoldo Sarra, Andrea Aiello, and Florian Marquardt

We derive a well-defined renormalized version of mutual information that allows us to estimate the dependence between continuous random variables in the important case when one is deterministically dependent on the other. This is the situation relevant for feature extraction, where the goal is to pr…

[Phys. Rev. Lett. 126, 200601] Published Mon May 17, 2021

Vacillating time: a metaphysics for time travel and Geachianism

Abstract

‘Past vacillators’ believe that what was once the case may change over time. This has obvious applications to the possibility of changing the past via time travel. ‘Future vacillators’ believe that some things will happen and yet, later, will not. Further to issues in time travel, future vacillation has applications when it comes to ‘Geachian’ views about the open future. This paper argues that if you deny that the ‘earlier than’ and ‘later than’ relations are converses of one another then you can develop metaphysical systems underpinning the possibility of such vacillation.

A kind route from grounding to fundamentality

Abstract

I offer an account of fundamentality for facts in terms of metaphysical grounding. The account does justice to the idea that whether a fact is absolutely fundamental, and whether a fact is more fundamental than, or as fundamental as, another fact, are a matter of where in a grounding-induced hierarchy of kinds of facts these facts appear.