arXiv subjects

Juan Ramón Muñoz de Nova

Publications and source records attributed to Juan Ramón Muñoz de Nova.

16 recordsLinked to original sources

arXiv2026

Quantum Information in High-Energy Physics: a top subject

As a work selected for the Frontiers of Science Award, we present in the Proceedings of the ICBS an overview of how the techniques from the field of Quantum Information (QI) can be implemented in High-Energy Physics (HEP), including also some novel insights. We focus on the paradigmatic case of the top quark, a drosophila of a relativistic qubit. We study the presence of entanglement, perhaps the most genuine feature of Quantum Mechanics, in top-antitop quark production in high-energy colliders such as the LHC. We also analyze our experimental proposal of a quantum tomography protocol for the top-antitop quark pair, eventually leading to the entanglement observations by the ATLAS and CMS collaborations, which constituted the highest-energy observations of entanglement ever. We discuss how the concepts and techniques developed in our work have effectively spawned an already vast and rich field of QI in HEP.

hep-ph↗

arXiv2026

Nonlocal advantage of quantum coherence in tau-lepton pairs from electron--positron collisions

Quantum correlations have recently attracted significant attention in collider physics, with Nonlocal Advantage of Quantum Coherence (NAQC) representing the strongest form of quantum correlation studied so far. Owing to its strength, NAQC is considerably more challenging to observe than Bell nonlocality since it is only present in narrower regions of phase space. Unlike other systems, tau-lepton pair ($τ^+τ^-$) production in electron--positron ($e^+e^-$) collisions provides an ideal testing ground, as it exhibits strong quantum correlations and, in particular, NAQC over a large region of phase space. In this paper, we investigate NAQC in $e^+e^- \to τ^+τ^-$ production at center-of-mass energies of 10.58 and 91.19~GeV, corresponding to the ongoing Belle~II and future FCC-$ee$ experiments, respectively. Remarkably, for our experimental proposal, we develop a dedicated NAQC witness, which allows to certify NAQC presence by measuring one single magnitude. We estimate the experimental sensitivities needed to establish the presence of NAQC, finding that a large fraction of the number of events (specifically, 0.18 for Belle~II and 0.31 for FCC-$ee$) contribute to the NAQC signal. A 5$σ$ observation of NAQC requires a precision of approximately 1\% at Belle~II, while a precision of a few percent is sufficient at FCC-$ee$. The resulting observation would constitute the strongest form of quantum correlation measured in a collider to date. In addition, we design an experimental scheme to implement the steering game leading to the NAQC definition, representing the first implementation of a steering game in a high-energy collider. Our results are easily extendable to other electron--positron colliders with different center-of-mass energies.

quant-ph↗

arXiv2026

Experimental characterization of the hierarchy of quantum correlations in top quark pairs

Recent results from the Large Hadron Collider have demonstrated quantum entanglement of top quark-antiquark pairs using the spin degrees of freedom. Based on the doubly differential measurement of the spin density matrix of the top quark and antiquark performed by the CMS collaboration in the helicity and beam bases, we evaluate a set of quantum observables, including discord, steerability, Bell correlation, and magic. These observables allow for a quantitative characterization of the quantum correlations present in a top quark-antiquark system, thus enabling an interpretation of collider data in terms of quantum states and their properties. Discord is observed to be greater than zero with a significance of more than 5 standard deviations ($σ$) in several regions of phase space, some of which correspond to separable quantum states. Evidence for steerability is established for the first time in a high-energy system, with a significance of more than 3$σ$. No Bell correlation is observed within the currently probed phase space, in agreement with the theoretical prediction. These results experimentally corroborate the hierarchy of quantum correlations in top quarks with discord being the most basic form of quantum correlation, followed by entanglement, steerability, and Bell correlation. The significance of nonzero magic, which is a complementary observable to the quantum correlation hierarchy, is found to exceed 5$σ$ in several regions of phase space.

quant-ph↗

arXiv2026

Time Crystal from Self-Amplification of Spontaneous Analog Hawking Radiation

We propose a time crystal based on a quantum black-hole laser, where the genuinely spontaneous character of the symmetry breaking stems from the self-amplification of spontaneous Hawking radiation. The resulting Hawking time crystal (HTC) is characterized by the periodic dependence of the out-of-time density-density correlation function, while equal-time observables are time independent because they embody averages over different realizations with a random oscillation phase. The HTC provides a nonlinear periodic analog of the Andreev-Hawking effect, exhibiting anticorrelation bands resulting from the spontaneous, quantum emission of pairs of dispersive waves and solitons into the upstream and downstream regions. Remarkably, we prove that any parametric amplifier has associated a time operator, which leads to a unique characterization of the time-crystal formation in terms of two time operators: one associated with the initial black-hole laser and another associated with the final spontaneous Floquet state.

quant-ph↗

arXiv2025

Observation of stationary spontaneous Hawking radiation and the time evolution of an analogue black hole

The emission of Hawking radiation from a black hole was predicted to be stationary, which is necessary for the correspondence between Hawking radiation and black-body radiation. Spontaneous Hawking radiation was observed in analogue black holes in atomic Bose-Einstein condensates, although the stationarity was not probed. Here, we confirm that the spontaneous Hawking radiation is stationary, by observing such a system at six different times. Furthermore, we follow the time evolution of Hawking radiation and compare and contrast it with predictions for real black holes. We observe the ramp up of Hawking radiation followed by stationary spontaneous emission, similar to a real black hole. The end of the spontaneous Hawking radiation is marked by the formation of an inner horizon, which is seen to cause stimulated Hawking radiation as predicted. We find that the stimulated Hawking and partner particles are directly observable, and that the stimulated emission evolves from multi-mode to monochromatic. Numerical simulations suggest that Bogoliubov-Cherenkov-Landau stimulation predominates, rather than black-hole lasing.

gr-qc↗

arXiv2025

Quantum Information meets High-Energy Physics: Input to the update of the European Strategy for Particle Physics

Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown and has gathered the attention of the scientific community. For the range of particles and fundamental interactions involved, particle colliders provide a novel environment where quantum information theory can be probed, with energies exceeding by about 12 orders of magnitude those employed in dedicated laboratory setups. Furthermore, collider detectors have inherent advantages in performing certain quantum information measurements, and allow for the reconstruction of the state of the system under consideration via quantum state tomography. Here, we elaborate on the potential, challenges, and goals of this innovative and rapidly evolving line of research and discuss its expected impact on both quantum information theory and high-energy physics.

hep-ph↗

arXiv2025

Simultaneous symmetry breaking in spontaneous Floquet states: temporal Floquet-Nambu-Goldstone modes, Floquet thermodynamics, and the time operator

We study simultaneous symmetry breaking in spontaneous Floquet states, focusing on the specific case of an atomic condensate. We first describe the quantization of the Nambu-Goldstone (NG) modes for a stationary state simultaneously breaking several symmetries of the Hamiltonian by invoking the generalized Gibbs ensemble, which enables a thermodynamical description of the problem. The quantization procedure involves a Berry-Gibbs connection, which depends on the macroscopic conserved charges associated to each broken symmetry and whose curvature is not invariant under generalized gauge transformations. We extend the formalism to Floquet states, where Goldstone theorem translates into the emergence of Floquet-Nambu-Goldstone (FNG) modes with zero quasi-energy. In the case of a spontaneous Floquet state, there is a genuine temporal FNG mode arising from the continuous time-translation symmetry breaking, whose quantum amplitude provides a rare realization of a time operator in Quantum Mechanics. Furthermore, since they conserve energy, spontaneous Floquet states can be shown to possess a conserved Floquet charge. Conventional Floquet systems also admit a thermodynamic description in terms of the Floquet enthalpy, the Legendre transform of the energy with respect to the Floquet charge, as these operate at fixed frequency. We apply our formalism to a particular realization of spontaneous Floquet state, the CES state, which breaks $U(1)$ and time-translation symmetries, representing a time supersolid. We numerically compute its density-density correlations, predicted to be dominated by the temporal FNG mode at long times, observing a remarkable agreement between simulation and theory. Based on these results, we propose a feasible experimental scheme to observe the temporal FNG mode of the CES state.

quant-ph↗

arXiv2025

Entanglement and Bell nonlocality with bottom-quark pairs at hadron colliders

It has been shown that entanglement and Bell nonlocality, which are key concepts in Quantum Mechanics, can be probed in high-energy colliders via processes of fundamental particle scattering. In fact, the ATLAS and CMS collaborations have measured entanglement using top-quark pairs produced in proton-proton collisions at the LHC. Recently, it was shown that spin correlations can be measured in pairs of bottom quarks at the LHC, despite the fact that bottom quarks, unlike top quarks, hadronize before decaying. Here, we demonstrate that quantum correlations can also be studied using bottom-quark pairs, and analyze the feasibility of the observation of entanglement and Bell nonlocality in several collider experiments. Given the low mass of the bottom quark relative to typical energies accessible at the LHC, many of the bottom-quark pairs are in the ultrarelativistic regime, where they can exhibit strong spin entanglement. We find that entanglement of bottom-quark pairs may be measurable even with the LHC Run 2 data, especially with the CMS $B$ parking dataset, while observation of Bell nonlocality may become feasible at the high-luminosity phase of the LHC.

hep-ph↗

arXiv2024

Resonant analogue configurations in atomic condensates

As a contribution to a memorial volume, we provide a comprehensive discussion of resonant configurations in analogue gravity, focusing on its implementation in atomic condensates and combining review features with original insights and calculations. In particular, we analyze the analogues of the Andreev and Hawking effects using a microscopic description based on the Bogoliubov approximation. We contemplate several resonant scenarios whose efficiency to enhance anomalous scattering processes is compared to that of non-resonant setups. The presence of quantum signatures in analogue configurations, such as the violation of Cauchy-Schwarz inequalities or entanglement, is analyzed, observing that resonant configurations highly increase the entanglement signal, especially for the Andreev effect. We also discuss how these results have served as inspiration for the rapidly expanding field of quantum information in high-energy colliders. Finally, we study the physics of black-hole lasers as further examples of resonant analogue structures, distinguishing three stages in its time evolution. For short times, we compute the linear and non-linear spectrum for different models. For intermediate times, we generalize the current analysis of the BHL-BCL crossover. For long times, we discuss the emerging concept of spontaneous Floquet state and its potential implications.

cond-mat.quant-gas↗

arXiv2024

The BHL-BCL crossover: from nonlinear to linear quantum amplification

The black-hole laser (BHL) effect is the self-amplification of Hawking radiation between a pair of horizons which act as a resonant cavity. In a flowing atomic condensate, the BHL effect arises in a finite supersonic region, where Bogoliubov-Cherenkov-Landau (BCL) radiation is resonantly excited by any static perturbation. Thus, experimental attempts to produce a BHL unavoidably deal with the presence of a strong BCL background, making the observation of the BHL effect still a major challenge in the analogue gravity field. Here, we perform a theoretical study of the BHL-BCL crossover using an idealized model where both phenomena can be unambiguously isolated. By drawing an analogy with an unstable pendulum, we distinguish three main regimes according to the interplay between quantum fluctuations and classical stimulation: quantum BHL, classical BHL, and BCL. Based on quite general scaling arguments, the nonlinear amplification of quantum fluctuations up to saturation is identified as the most robust trait of a quantum BHL. A classical BHL behaves instead as a linear quantum amplifier, where the output is proportional to the input. The BCL regime also acts as a linear quantum amplifier, but its gain is exponentially smaller as compared to a classical BHL. Complementary signatures of black-hole lasing are a decrease in the amplification for increasing BCL amplitude or a nonmonotonic dependence of the growth rate with respect to the background parameters. We also identify interesting analogue phenomena such as Hawking-stimulated white-hole radiation or quantum BCL-stimulated Hawking radiation. The results of this work not only are of interest for analogue gravity, where they help to distinguish each phenomenon and to design experimental schemes for a clear observation of the BHL effect, but they also open the prospect of finding applications of analogue concepts in quantum technologies.

cond-mat.quant-gas↗

arXiv2023

Quantum discord and steering in top quarks at the LHC

Top quarks have been recently shown to be a promising system to study quantum information at the highest-energy scale available. The current lines of research mostly discuss topics such as entanglement, Bell nonlocality or quantum tomography. Here, we provide the full picture of quantum correlations in top quarks by studying also quantum discord and steering. We find that both phenomena are present at the LHC. In particular, quantum discord in a separable quantum state is expected to be detected with high-statistical significance. Interestingly, due to the singular nature of the measurement process, quantum discord can be measured following its original definition, and the steering ellipsoid can be experimentally reconstructed, both highly-demanding measurements in conventional setups. In contrast to entanglement, the asymmetric nature of quantum discord and steering can provide witnesses of $CP$-violating physics beyond the Standard Model.

quant-ph↗

arXiv2022

Quantum information with top quarks in QCD

Top quarks represent unique high-energy systems since their spin correlations can be measured, thus allowing to study fundamental aspects of quantum mechanics with qubits at high-energy colliders. We present here the general framework of the quantum state of a top-antitop ($t\bar{t}$) quark pair produced through quantum chromodynamics (QCD) in a high-energy collider. We argue that, in general, the total quantum state that can be probed in a collider is given in terms of the production spin density matrix, which necessarily gives rise to a mixed state. We compute the quantum state of a $t\bar{t}$ pair produced from the most elementary QCD processes, finding the presence of entanglement and CHSH violation in different regions of phase space. We show that any realistic hadronic production of a $t\bar{t}$ pair is a statistical mixture of these elementary QCD processes. We focus on the experimentally relevant cases of proton-proton and proton-antiproton collisions, performed at the LHC and the Tevatron, analyzing the dependence of the quantum state with the energy of the collisions. We provide experimental observables for entanglement and CHSH-violation signatures. At the LHC, these signatures are given by the measurement of a single observable, which in the case of entanglement represents the violation of a Cauchy-Schwarz inequality. We extend the validity of the quantum tomography protocol for the $t\bar{t}$ pair proposed in the literature to more general quantum states, and for any production mechanism. Finally, we argue that a CHSH violation measured in a collider is only a weak form of violation of Bell's theorem, necessarily containing a number of loopholes.

quant-ph↗

arXiv2021

Entanglement and quantum tomography with top quarks at the LHC

Entanglement is a central subject in quantum mechanics. Due to its genuine relativistic behavior and fundamental nature, high-energy colliders are attractive systems for the experimental study of fundamental aspects of quantum mechanics. We propose the detection of entanglement between the spins of top-antitop-quark pairs at the LHC, representing the first proposal of entanglement detection in a pair of quarks, and also the entanglement observation at the highest energy scale so far. We show that entanglement can be observed by direct measurement of the angular separation between the leptons arising from the decay of the top-antitop pair. The detection can be achieved with high statistical significance, using the current data recorded during Run 2 at the LHC. In addition, we develop a simple protocol for the quantum tomography of the top-antitop pair. This experimental technique reconstructs the quantum state of the system, providing a new experimental tool to test theoretical predictions. Our work explicitly implements canonical experimental techniques in quantum information in a two-qubit high-energy system, paving the way to use high-energy colliders to also study quantum information aspects.

quant-ph↗

arXiv2018

Observation of thermal Hawking radiation at the Hawking temperature in an analogue black hole

We measure the correlation spectrum of the Hawking radiation emitted by an analogue black hole and find it to be thermal at the Hawking temperature implied by the analogue surface gravity. The Hawking radiation is in the regime of linear dispersion, in analogy with a real black hole. Furthermore, the radiation inside of the black hole is seen to be composed of negative-energy partners only. This work confirms the prediction of Hawking's theory regarding the value of the Hawking temperature, as well as the thermality of the spectrum. The thermality of Hawking radiation is the root of the information paradox. The correlations between the Hawking and partner particles imply that the analogue black hole has no analogue firewall.

gr-qc↗

arXiv2017

Non-linear stationary solutions in realistic models for analog black-hole lasers

From both a theoretical and an experimental point of view, Bose-Einstein condensates are good candidates for studying gravitational analogues of black holes and black-hole lasers. In particular, a recent experiment has shown that a black-hole laser configuration can be created in the laboratory. However, the most considered theoretical models for analog black-hole lasers are quite difficult to implement experimentally. In order to fill this gap, we devote this work to present more realistic models for black-hole lasers. For that purpose, we first prove that, by symmetrically extending every black-hole configuration, one can obtain a black-hole laser configuration with an arbitrarily large supersonic region. Based on this result, we propose the use of an attractive square well and a double delta-barrier, which can be implemented using standard experimental tools, for studying black-hole lasers. We also compute the different stationary states of these setups, identifying the true ground state of the system and discussing the relation between the obtained solutions and the appearance of dynamical instabilities.

cond-mat.quant-gas↗

arXiv2016

Self-amplifying Hawking radiation and its background: a numerical study

We numerically study an analogue black hole with two horizons with similar parameters to a recent experiment. We find that the Hawking radiation exists on a background which contains a density oscillation, a zero-frequency ripple. The Hawking radiation evolves from spontaneous to self-amplifying, while the background ripple grows steadily with no qualitative change. It is seen that the self-amplifying Hawking radiation has a non-zero frequency. The background ripple appears even before the inner horizon is created, in contrast to predictions. This work is in agreement with the recent observation of self-amplifying Hawking radiation, and explains some of the features seen. In contrast to recent works, our study differentiates between the Hawking radiation observed, and the evolution of the background.

cond-mat.quant-gas↗