# Weekly Papers on Quantum Foundations (48)

Biology and medicine in the landscape of quantum advantages. (arXiv:2112.00760v1 [quant-ph])

Quantum computing holds significant potential for applications in biology and medicine, spanning from the simulation of biomolecules to machine learning approaches for subtyping cancers on the basis of clinical features. This potential is encapsulated by the concept of a quantum advantage, which is typically contingent on a reduction in the consumption of a computational resource, such as time, space, or data. Here, we distill the concept of a quantum advantage into a simple framework that we hope will aid researchers in biology and medicine pursuing the development of quantum applications. We then apply this framework to a wide variety of computational problems relevant to these domains in an effort to i) assess the potential of quantum advantages in specific application areas and ii) identify gaps that may be addressed with novel quantum approaches. Bearing in mind the rapid pace of change in the fields of quantum computing and classical algorithms, we aim to provide an extensive survey of applications in biology and medicine that may lead to practical quantum advantages.

The Berry phase from the entanglement of future and past light cones: detecting the timelike Unruh effec. (arXiv:2112.00898v1 [gr-qc])

The Unruh effect can not only arise out of the entanglement between modes of left and right Rindler wedges, but also between modes of future and past light cones. We explore the geometric phase resulting from this timelike entanglement between the future and past, showing that it can be captured in a simple $\Lambda$-system. This provides an alternative paradigm to the Unruh-deWitt detector. The Unruh effect has not been experimentally verified because the accelerations needed to excite a response from Unruh-deWitt detectors are prohibitively large. We demonstrate that a stationary but time-dependent $\Lambda$-system detects the timelike Unruh effect with current technology.

A Quantum Informational Approach to the Problem of Time. (arXiv:2112.00918v1 [gr-qc])

Several novel approaches have been proposed to resolve the problem of time by relating it to change. We argue using quantum information theory that the Hamiltonian constraint in quantum gravity cannot probe change, so it cannot be used to obtain a meaningful notion of time. This is due to the absence of quantum Fisher information with respect to the quantum Hamiltonian of a time-reparametization invariant system. We also observe that the inability of this Hamiltonian to probe change can be related to its inability to discriminate between states of such a system. However, if the time-reparametization symmetry is spontaneously broken due to the formation of quantum cosmological time crystals, these problems can be resolved, and it is possible for time to emerge in quantum gravity.

How to engineer a quantum wavefunction. (arXiv:2112.01105v1 [quant-ph])

In a conventional experiment, inductive inferences between source and target systems are typically justified with reference to a uniformity principle between systems of the same material type. In an analogue quantum simulation, by contrast, scientists aim to learn about target quantum systems of one material type via an experiment on a source quantum system of a different material type. In this paper, we argue that such an inference can be justified by reference to the two quantum systems being of the same empirical type. We illustrate this novel experimental practice of wavefunction engineering with reference to the example of Bose-Hubbard systems.

Optimal unambiguous discrimination and quantum nonlocality without entanglement: locking and unlocking by post-measurement information. (arXiv:2112.01139v1 [quant-ph])

The phenomenon of nonlocality without entanglement(NLWE) arises in discriminating multi-party quantum separable states. Recently, it has been found that the post-measurement information about the prepared subensemble can lock or unlock NLWE in minimum-error discrimination of non-orthogonal separable states. Thus It is natrual to ask whether the availability of the post-measurement information can influence on the occurrence of NLWE even in other state-discrimination stratigies. Here, we show that the post-measurement information can be used to lock as well as unlock the occurence of NLWE in terms of optimal nambiguous discrimination. Our results can provide a useful application for hiding or sharing information based on non-orthogonal separable states.

The second law of thermodynamics as a deterministic theorem for quantum spin systems. (arXiv:2112.01175v1 [math-ph])

The second law of thermodynamics, viewed as a theorem asserting the growth of the mean (Gibbs-von Neumann) entropy of a class of quantum spin systems undergoing automorphic (unitary) adiabatic transformations, is proved. Non-automorphic interactions with the environment, although known to produce on the average a strict reduction of the entropy of systems with finite number of degrees of freedom, are proved to conserve the mean entropy on the average, for some models of quantum spin systems. Some related results on the approach (or return) to equilibrium are also reviewed. The results depend crucially on two properties of the mean entropy, proved by Robinson and Ruelle for classical systems, and Lanford and Robinson for quantum lattice systems: upper semicontinuity and affinity.

A Quantum Annealing Approach to Reduce Covid-19 Spread on College Campuses. (arXiv:2112.01220v1 [cs.CY])

Disruptions of university campuses caused by COVID-19 have motivated strategies to prevent the spread of infectious diseases while maintaining some level of in person learning. In response, the proposed approach recursively applied a quantum annealing algorithm for Max-Cut optimization on D-Wave Systems, which grouped students into cohorts such that the number of possible infection events via shared classrooms was minimized. To test this approach, available coursework data was used to generate highly clustered course enrollment networks representing students and the classes they share. The algorithm was then recursively called on these networks to group students, and a disease model was applied to forecast disease spread. Simulation results showed that under some assumptions on disease statistics and methods of spread, the quantum grouping method reduced both the total and peak percentage of infected students when compared against random groupings of students. Scaling to larger networks, it is possible that this quantum annealer-assisted grouping approach may provide practical advantage over classical approaches. This paper, however, is strictly a proof-of-concept demonstration of the approach and is not intended to argue for a quantum speedup.

Are Brain-Computer Interfaces Feasible with Integrated Photonic Chips?. (arXiv:2112.01249v1 [q-bio.NC])

The present paper examines the viability of a radically novel idea for brain-computer interface (BCI), which could lead to novel technological, experimental and clinical applications. BCIs are computer-based systems that enable either one-way or two-way communication between a living brain and an external machine. BCIs read-out brain signals and transduce them into task commands, which are performed by a machine. In closed-loop, the machine can stimulate the brain with appropriate signals. In recent years, it has been shown that there is some ultraweak light emission from neurons within or close to the visible and near-infrared parts of the optical spectrum. Such ultraweak photon emission (UPE) reflects the cellular (and body) oxidative status, and compelling pieces of evidence are beginning to emerge that UPE may well play an informational role in neuronal functions. In fact, several experiments point to a direct correlation between UPE intensity and neural activity, oxidative reactions, EEG activity, cerebral blood flow, cerebral energy metabolism, and release of glutamate. Here, we propose a novel skull implant BCI that uses UPE. We suggest that a photonic integrated chip installed on the interior surface of the skull may enable a new form of extraction of the relevant features from the UPE signals. In the current technology landscape, photonic technologies advance rapidly and poised to overtake many electrical technologies, due to their unique advantages, such as miniaturization, high speed, low thermal effects, and large integration capacity that allow for high yield, volume manufacturing, and lower cost. For our proposed BCI, we make some major conjectures, which need to be experimentally verified, and hence we discuss the controversial parts, feasibility of technology and limitations, and potential impact of this envisaged technology if successfully implemented in the future.

Emergent universe revisited through the CSL theory. (arXiv:2108.01472v2 [gr-qc] UPDATED)

In this work we analyze how the spectrum of primordial scalar perturbations is modified, within the emergent universe scenario, when a particular version of the Continuous Spontaneous Localization (CSL) model is incorporated as the generating mechanism of initial perturbations, providing also an explanation to the quantum-to-classical transition of such perturbations. On the other hand, a phase of super-inflation, prior to slow-roll inflation, is a characteristic feature of the emergent universe hypothesis. In recent works, it was shown that the super-inflation phase could generically induce a suppression of the temperature anisotropies of the CMB at large angular scales. We study here under what conditions the CSL maintains or modifies these characteristics of the emergent universe and their compatibility with the CMB observations.

Detectable Gravitational Wave Signals from Inflationary Preheating. (arXiv:2112.00762v1 [hep-ph])

Authors: Yanou CuiEvangelos I. Sfakianakis

We consider gravitational wave (GW) production during preheating in hybrid inflation models where an axion-like waterfall field couples to Abelian gauge fields. Based on a linear analysis, we find that the GW signal from such models can be within the reach of a variety of foreseeable GW experiments such as LISA, AEDGE, ET and CE, and is close to that of LIGO A+, both in terms of frequency range and signal strength. Furthermore, the resultant GW signal is helically polarized and thus may distinguish itself from other sources of stochastic GW background. Finally, such models can produce primordial black holes that can compose dark matter and lead to merger events detectable by GW detectors.

Generalised proofs of the first law of entanglement entropy. (arXiv:2112.00972v1 [hep-th])

Authors: Marika TaylorLinus Too

In this paper we develop generalised proofs of the holographic first law of entanglement entropy using holographic renormalisation. These proofs establish the holographic first law for non-normalizable variations of the bulk metric, hence relaxing the boundary conditions imposed on variations in earlier works. Boundary and counterterm contributions to conserved charges computed via covariant phase space analysis have been explored previously. Here we discuss in detail how counterterm contributions are treated in the covariant phase approach to proving the first law. Our methodology would be applicable to generalizing other holographic information analyses to wider classes of gravitational backgrounds.

Stochastic Quantization of General Relativity \`a la Ricci-Flow. (arXiv:2112.01490v1 [gr-qc])

We follow a new pathway to the definition of the Stochastic Quantization (SQ), first proposed by Parisi and Wu, of the action functional yielding the Einstein equations. Hinging on the functional similarities between the Ricci-Flow equation and the SQ Langevin equations, we push forward a novel approach in which the stochastic time converges to the proper time of a space-like foliation in the equilibrium limit. This procedure in turn requires adding to the usual symmetric connection a projective Weyl term that does not modify the classical equations of motion. Furthermore, we express the starting system of equations using the Arnowitt-Deser-Misner (ADM) variables and their conjugated Hamiltonian momenta. Such a choice is instrumental for understanding the newly derived equations in terms of the breaking the diffeomorphism invariance of the classical theory, which will hold on average at the steady state. We comment on the physical interpretation of the Ricci flow equations, and argue how they can naturally provide, in a geometrical way, the renormalization group equation for gravity theories. In the general setting, the equation associated to the shift vector yields the Navier-Stokes equation with a stochastic source. Moreover, we show that the fluctuations of the metric tensor components around the equilibrium configurations, far away from the horizon of a Schwarzschild black hole, are forced by the Ricci flow to follow the Kardar-Parisi-Zhang equation, whose probabilistic distribution can yield an intermittent statistics. We finally comment on the possible applications of this novel scenario to the cosmological constant, arguing that the Ricci flow may provide a solution to the Hubble tension, as a macroscopic effect of the quantum fluctuation of the metric tensor.

The Chances of Propensities

Suárez, Mauricio (2016) The Chances of Propensities. [Preprint]

What is So Special about Analogue Simulations?

Nappo, Francesco (2021) What is So Special about Analogue Simulations? [Preprint]

Quantum and Classical Temporal Correlations in $(1+1)\mathrm{D}$ Quantum Cellular Automata

Author(s): Edward Gillman, Federico Carollo, and Igor Lesanovsky

We employ (1+1)-dimensional quantum cellular automata to study the evolution of entanglement and coherence near criticality in quantum systems that display nonequilibrium steady-state phase transitions. This construction permits direct access to the entire space-time structure of the underlying none…

[Phys. Rev. Lett. 127, 230502] Published Wed Dec 01, 2021

Against the disappearance of spacetime in quantum gravity

Abstract

This paper argues against the proposal to draw from current research into a physical theory of quantum gravity the ontological conclusion that spacetime or spatiotemporal relations are not fundamental. As things stand, the status of this proposal is like the one of all the other claims about radical changes in ontology that were made during the development of quantum mechanics and quantum field theory. However, none of these claims held up to scrutiny as a consequence of the physics once the theory was established and a serious discussion about its ontology had begun. Furthermore, the paper argues that if spacetime is to be recovered through a functionalist procedure in a theory that admits no fundamental spacetime, standard functionalism cannot serve as a model: all the known functional definitions are definitions in terms of a causal role for the motion of physical objects and hence presuppose spatiotemporal relations.

Spatial experience, spatial reality, and two paths to primitivism

Abstract

I explore two views about the relationship between spatial experience and spatial reality: spatial functionalism and spatial presentationalism. Roughly, spatial functionalism claims that the instantiated spatial properties are those playing a certain causal role in producing spatial experience while spatial presentationalism claims that the instantiated spatial properties include those presented in spatial experience. I argue that each view, in its own way, leads to an ontologically inflationary form of primitivism: whereas spatial functionalism leads to primitivism about phenomenal representation, spatial presentationalism leads to primitivism about spatial properties. I conclude by discussing how to adjudicate between spatial functionalism and spatial presentationalism.

Degeneration and Entropy

Chua, Eugene Y. S. (2021) Degeneration and Entropy. [Preprint]

Double charge wave

Nature Physics, Published online: 30 November 2021; doi:10.1038/s41567-021-01457-z

Charge density waves are the periodic spatial modulation of electrons in a solid. A new experiment reveals that they can originate from two different electronic bands in a prototypical transition metal dichalcogenide, NbSe2.

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 (166679). ISSN 0030-4026

Forced Changes Only: A New Take on the Law of Inertia

Hoek, Daniel (2021) Forced Changes Only: A New Take on the Law of Inertia. [Preprint]

The physics and metaphysics of Tychistic Bohmian Mechanics

Duerr, Patrick and Ehmann, Alexander (2021) The physics and metaphysics of Tychistic Bohmian Mechanics. Studies in History and Philosophy of Science Part A, 90. pp. 168-183. ISSN 00393681

Are ‘Particles’ in Quantum Mechanics “Just a Way of Talking”?

de Ronde, Christian and Fernández Mouján, Raimundo (2021) Are ‘Particles’ in Quantum Mechanics “Just a Way of Talking”? [Preprint]

Could Charge and Mass be Universals?

Gilton, Marian (2020) Could Charge and Mass be Universals? [Preprint]

Setting the demons loose: computational irreducibility does not guarantee unpredictability or emergence

Tabatabaei Ghomi, Hamed (2021) Setting the demons loose: computational irreducibility does not guarantee unpredictability or emergence. [Preprint]