arXiv subjects

Ivan Agullo

Publications and source records attributed to Ivan Agullo.

At least 19 recordsLinked to original sources

arXiv2026

Ad Astra White Paper: A Pitch for the Next 25 Years of NASA's Physics of the Cosmos Program

Astrophysical observations of our universe have been key to our understanding of how the universe works. Shortly after the turn of the millennium, the National Research Council delivered \textit{Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century}. In the subsequent quarter-century, we have made substantial progress in answering each question. These advancements have, in part, arisen because of the success of major US facilities across several domains of physics, guided by long-term planning documents which still largely focus on these questions. This report seeks to provide a status update on each question, and to outline what space-based facilities are crucial for future progress, intended to guide NASA's preparatory work for the Astro2030 Decadal.

astro-ph.IM↗

arXiv2025

Partner-mode overlap as a symplectic-invariant measure of correlations in Gaussian quantum field theories

We introduce a locally symplectic-invariant quantifier of correlations between arbitrary bosonic Gaussian modes, with particular emphasis on quantum field theory. The quantity, denoted by~$\mathcal{D}^{\mathrm{sym}}$, admits a simple geometric interpretation as the symmetric overlap between each mode and the purification partner of the other, providing a direct geometric characterization of how correlations are distributed between modes. We derive a necessary and sufficient criterion for two-mode Gaussian entanglement in terms of $\mathcal{D}^{\mathrm{sym}}$, placing on firm quantitative footing the intuition that the entanglement of a localized mode is encoded in the spatial support of its purification partner. We demonstrate the framework for wavepacket modes of a scalar quantum field in Minkowski spacetime (illustrating how the geometry of partner modes reveals the spatial structure of quantum correlations) and discuss extensions to multimode systems and mixed Gaussian states.

quant-ph↗

arXiv2025

Vacuum-purified Hawking radiation from evaporating black holes: Lessons from moving mirrors

This article investigates the possibility that Hawking-like quanta emitted by a moving mirror can be purified by late-time vacuum fluctuations, as proposed in Hotta, Sch\"utzhold and Unruh [Phys. Rev. D 91, 124060 (2015)]. Our motivation originates from recent discussions in Wald [Phys. Rev. D 100, 065019 (2019)] and Osawa et al. [Phys. Rev. D 110, 025023 (2024)] on whether vacuum purification necessarily entails a prohibitively large (indirect) energy cost, and our goal is to help clarify this issue. We identify the aspects of the mirror trajectory that determine the partners of Hawking quanta, as well as those that govern the energy carried to future null infinity. This allows us to highlight a fundamental disconnection within quantum field theory between the fluxes of quantum information (or purification) and energy. Throughout, we focus on quantities such as local correlation functions and energy fluxes, thereby avoiding reliance on a particle-based interpretation. Finally, we introduce an analytic mirror trajectory that produces Hawking radiation with an adiabatically varying temperature, mimicking the emission from an evaporating black hole. Our analysis identifies constraints on the mirror trajectory under which vacuum purification remains compatible with a prescribed energy budget, and we discuss the lessons that may be drawn from this model for realistic evaporating black holes.

gr-qc↗

arXiv2025

Correlation and Entanglement partners in Gaussian systems

We introduce a framework to identify where the total correlations and entanglement with a chosen degree of freedom reside within the rest of a system, in the context of bosonic many-body Gaussian quantum systems. Our results are organized into two main propositions. First, for pure Gaussian states, we show that every correlated mode possesses a unique single-degree-of-freedom partner that fully captures its correlations (consisting of entanglement), and we provide an explicit construction of this partner from the complex structure of the system's state. Second, for mixed Gaussian states, we constructively demonstrate that the notion of a partner subsystem splits into two: a correlation partner, which contains all classical and quantum correlations and need not correspond to a single degree of freedom, and an entanglement partner, which is always at most single-mode. Finally, we extend the construction of partners to multi-mode subsystems. Together, these results provide conceptual practical tools to study how bipartite correlations and entanglement are structured and where they can be found in complex Gaussian many-body systems.

quant-ph↗

arXiv2025

Entanglement and correlations between local observables in de Sitter spacetime

Studies of quantum field entanglement in de Sitter space based on the von Neumann entropy of local patches have concluded that curvature enhances entanglement between regions and their complements. Similar conclusions about entanglement enhancement have been reached in analyses of Fourier modes in the cosmological patch of de Sitter space. We challenge this interpretation by adopting a fully local approach: examining entanglement between pairs of field modes compactly supported within de Sitter's cosmological patch. Our approach is formulated in terms of the properties of a metric tensor and an associated complex structure induced by the Bunch-Davies vacuum on the classical phase space. We find that increasing curvature increases correlations between local modes but, somewhat counterintuitively, decreases their entanglement. Our methods allow us to characterize how entanglement is spatially distributed, revealing that a cosmological constant, even if tiny, qualitatively alters the vacuum's entanglement structure. We show that our results are compatible with previous entropy-based studies when properly interpreted. Our findings have implications for entanglement between observables generated during cosmic inflation.

gr-qc↗

arXiv2025

Multidisciplinary Science in the Multimessenger Era

Astrophysical observations of the cosmos allow us to probe extreme physics and answer foundational questions on our universe. Modern astronomy is increasingly operating under a holistic approach, probing the same question with multiple diagnostics including how sources vary over time, how they appear across the electromagnetic spectrum, and through their other signatures, including gravitational waves, neutrinos, cosmic rays, and dust on Earth. Astrophysical observations are now reaching the point where approximate physics models are insufficient. Key sources of interest are explosive transients, whose understanding requires multidisciplinary studies at the intersection of astrophysics, gravity, nuclear science, plasma physics, fluid dynamics and turbulence, computation, particle physics, atomic, molecular, and optical science, condensed matter and materials science, radiation transport, and high energy density physics. This white paper provides an overview of the major scientific advances that lay at the intersection of physics and astronomy and are best probed through time-domain and multimessenger astrophysics, an exploration of how multidisciplinary science can be fostered, and introductory descriptions of the relevant scientific disciplines and key astrophysical sources of interest.

astro-ph.HE↗

arXiv2024

Bell's shadows from satellites

Establishing reliable quantum links between a network of satellites and ground stations is a crucial step towards realizing a wide range of satellite-based quantum protocols, including global quantum networks, distributed sensing, quantum key distribution, and quantum clock synchronization. In this article, we envision a network of satellites and ground stations where quantum links are created through the exchange of entangled photon pairs. We simulate the dynamics of a satellite constellation and a set of Bell tests between the constellation and ground stations. We identify the regions on Earth where Bell tests can be successfully conducted with a satellite or a set of them, at a specified level of confidence. These regions move with the constellation and will be referred to as "Bell violation shadows". We demonstrate that these shadows provide valuable insights for the study and evaluation of many satellite-mediated or satellite-assisted quantum protocols.

quant-ph↗

arXiv2024

Toward the Observation of Entangled Pairs in BEC analogue Expanding Universes

Pair creation is a fundamental prediction of quantum field theory in curved spacetimes. While classical aspects of this phenomenon have been observed, the experimental confirmation of its quantum origin remains elusive. In this article, we quantify the entanglement produced by pair creation in two dimensional Bose-Einstein Condensate (BEC) analogues of expanding universes and examine the impact of various experimental factors, including decoherence from thermal noise and losses. Our analysis evaluates the feasibility of detecting entanglement in these systems and identifies optimal experimental configurations for achieving this goal. Focusing on the experimental setup detailed in \cite{Viermann:2022wgw}, we demonstrate that entanglement can be observed in these BEC analogues at a significance level of $\sim 2\sigma$ with current capabilities, and at $\gtrsim 3.3\sigma$ with modest improvements. Achieving this would provide unequivocal evidence of the quantum nature of pair creation and validate one of the most iconic predictions of quantum field theory in curved spacetimes.

gr-qc↗

arXiv2024

Inflation does not create entanglement in local observables

Using modern tools of relativistic quantum information, we compare entanglement of a free, massive scalar field in the Bunch-Davies vacuum in the cosmological patch of de Sitter spacetime with that in Minkowski spacetime. There is less entanglement between spatially localized field modes in de Sitter, despite the fact that there is more entanglement stored in the field on large scales. This shows that inflation does not produce entanglement between local observables.

gr-qc↗

arXiv2024

The multimode nature of spacetime entanglement in QFT

We demonstrate the presence of multimode entanglement in the vacuum state of a free, massless scalar quantum field in four-dimensional flat spacetime between two sets of field modes, each contained within a spacetime region that is causally disconnected from the other. This is true despite the fact that entanglement between pairs of individual field modes is sparse and appears only when the two individual modes are carefully selected. Our results reveal that, while entanglement between individual modes is limited, bipartite multimode entanglement in quantum field theory is ubiquitous. We further argue that such multimode entanglement is operationally extractable, and it forms the basis of the entanglement commonly discussed in entanglement harvesting protocols.

quant-ph↗

arXiv2024

Entangled pairs in evaporating black holes without event horizons

Investigations into Hawking radiation often assume a black hole model featuring an event horizon, despite the growing consensus that such causal structures may not exist in nature. While this assumption is not crucial for deriving the local properties of radiation at future null infinity, it plays a significant role in discussions about Hawking partners -- the field modes that purify Hawking radiation. This article aims to explore the definition and fate of Hawking partners in black hole scenarios where semiclassical mass loss due to Hawking radiation is considered. Our analysis avoids the assumption of event horizons and instead focuses on collapse processes that feature a trapped region bounded by a dynamical horizon. We derive the form of the partners, accounting for the effects of back-scattering. Furthermore, using these results and mild assumptions, we find that Hawking partners cannot "leak" out of the dynamical horizon to partially purify the Hawking radiation in the regime where general relativity coexists semiclassically with quantum field theory. This finding emphasizes the necessity for new physics, such as quantum gravity, to resolve the final fate of information.

gr-qc↗

arXiv2023

A quantum-assisted master clock in the sky: global synchronization from satellites at sub-nanosecond precision

This article develops a protocol to synchronize clocks on board a network of satellites equipped with quantum resources. We show that, in such a constellation, satellites reinforce each other's sync capabilities, forming a common clock that is more stable and precise than its constituents. We envision the resulting network as a master clock able to distribute time across the globe, providing the basis for a future quantum global navigation satellite system or a space-based quantum network. As an example of its capabilities, we show that a constellation of 50 satellites equipped with modest quantum resources, and distributed amongst 5 orbits at an altitude of 500 km, allows the synchronization of clocks spread across the globe at sub-nanosecond precision.

quant-ph↗

arXiv2023

Entanglement from superradiance and rotating quantum fluids of light

The amplification of radiation by superradiance is a universal phenomenon observed in numerous physical systems. We demonstrate that superradiant scattering generates entanglement for different input states, including coherent states, thereby establishing the inherently quantum nature of this phenomenon. To put these concepts to the test, we propose a novel approach to create horizonless ergoregions, which are nonetheless dynamically stable thanks to the dissipative dynamics of a polaritonic fluid of light. We numerically simulate the system to demonstrate the creation of a stable ergoregion. Subsequently, we investigate rotational superradiance within this system, with a primary focus on entanglement generation and the possibilities for its enhancement using current techniques. Our methods permit the investigation of quantum emission by rotational superradiance in state-of-the-art experiments, in which the input state can be controlled at will.

gr-qc↗

arXiv2023

Chiral fermion anomaly as a memory effect

We study the non-conservation of the chiral charge of Dirac fields between past and future null infinity due to the Adler-Bell-Jackiw chiral anomaly. In previous investigations \cite{dR21}, we found that this charge fails to be conserved if electromagnetic sources in the bulk emit circularly polarized radiation. In this article, we unravel yet another contribution coming from the non-zero, infrared "soft" charges of the external, electromagnetic field. This new contribution can be interpreted as another manifestation of the ordinary memory effect produced by transitions between different infrared sectors of Maxwell theory, but now on test quantum fields rather than on test classical particles. In other words, a flux of electromagnetic waves can leave a memory on quantum fermion states in the form of a permanent, net helicity. We elaborate this idea in both $1+1$ and $3+1$ dimensions. We also show that, in sharp contrast, gravitational infrared charges do not contribute to the fermion chiral anomaly.

hep-th↗

arXiv2023

Entanglement in an expanding toroidal Bose-Einstein condensate

Recent experiments have employed rapidly expanding toroidal Bose-Einstein condensates (BECs) to mimic the inflationary expansion in the early universe. One expected signature of the expansion in such experiments is spontaneous particle creation (of phonons) which is observable in density-density correlations. We study entanglement of these particles, which are known to result in a two-mode squeezed state. Using techniques for Gaussian states of continuous variable systems, we quantify the entanglement generated in this system, including effects such as decoherence and the use of an initially squeezed state, which can suppress and enhance entanglement, respectively. We also describe a protocol to experimentally measure the correlations entering the covariance matrix, allowing an experimental quantification of the entanglement properties of the inflationary BEC.

cond-mat.quant-gas↗

arXiv2023

Entanglement from rotating black holes in thermal baths

We extend previous efforts to quantify the entanglement generated in Hawking's evaporation process by including rotation and thermal environments (e.g. the cosmic microwave background). Both extensions are needed to describe real black holes in our universe. Leveraging techniques from Gaussian quantum information, we find that the black hole's ergoregion is an active source of quantum entanglement and that thermal environments drastically degrade entanglement generation. Our predictions are suitable to be tested in the lab using analogue platforms and also provide tools to assess the fate of quantum information for black holes in more generic settings.

gr-qc↗

arXiv2023

Synchronizing clocks via satellites using entangled photons: Effect of relative velocity on precision

A satellite-based scheme to perform clock synchronization between ground stations spread across the globe using quantum resources was proposed in [Phys. Rev. A 107, 022615 (2023)], based on the quantum clock synchronization (QCS) protocol developed in [Proc. SPIE 10547 (2018)]. Such a scheme could achieve synchronization up to the picosecond level over distances of thousands of kilometers. Nonetheless, the implementation of this QCS protocol is yet to be demonstrated experimentally in situations where the satellite velocities cannot be neglected, as is the case in many realistic scenarios. In this work, we develop analytical and numerical tools to study the effect of the relative velocity between the satellite and ground stations on the success of the QCS protocol. We conclude that the protocol can still run successfully if the data acquisition window is chosen appropriately. As a demonstration, we simulate the synchronization outcomes for cities across the continental United States using a single satellite in a LEO orbit, low-cost entanglement sources, portable atomic clocks, and avalanche detectors. We conclude that, after including the effect of relative motion, sub-nanosecond to picosecond level precision can still be achieved over distance scales of $\approx 4000$ kms. Such high precision synchronization is currently not achievable over long distances ($\gtrsim 100 km$) with standard classical techniques including the GPS. The simulation tools developed in this work are in principle applicable to other means of synchronizing clocks using entangled photons, which are expected to form the basis of future quantum networks like the Quantum Internet, distributed quantum sensing and Quantum GPS.

quant-ph↗

arXiv2023

How ubiquitous is entanglement in quantum field theory?

It is well known that entanglement is widespread in quantum field theory, in the following sense: every Reeh-Schlieder state contains entanglement between any two spatially separated regions. This applies, in particular, to the vacuum of a non-interacting scalar theory in Minkowski spacetime. Discussions on entanglement in field theory have focused mainly on subsystems containing infinitely many degrees of freedom -- typically, the field modes that are supported within a compact region of space. In this article, we study entanglement in subsystems made of finitely many field degrees of freedom, in a free scalar theory in $D+1$-dimensional Minkowski spacetime. The focus on finitely many modes of the field is motivated by the finite capabilities of real experiments. We find that entanglement between finite-dimensional subsystems is {\em not common at all}, and that one needs to carefully select the support of modes for entanglement to show up. We also find that entanglement is increasingly sparser in higher dimensions. We conclude that entanglement in Minkowski spacetime is significantly less ubiquitous than normally thought.

quant-ph↗