Publications (2024)
Total peer-reviewed articles: 132
Carbon Atom Condensation on NH3-H2O Ices. An Alternative Pathway to Interstellar Methanimine and Methylamine
Authors: Molpeceres, German; Tsuge, Masashi; Furuya, Kenji; Watanabe, Naoki; San Andres, David; Rivilla, Victor M.; Colzi, Laura; Aikawa, Yuri
Journal: JOURNAL OF PHYSICAL CHEMISTRY A
Publication date: 2024/05/06
Abstract: The recent discovery of the nature and behavior of carbon atoms interacting with interstellar ices has prompted a number of investigations on the chemistry initiated by carbon accretion on icy interstellar dust. In this work, we expand the range of processes promoted by carbon accretion to the chemistry initiated by the interaction of this atom with ammonia (NH3) using quantum chemical calculations. We found that carbon addition to the ammonia molecule forms a rather stable radical, CNH3, that is easily hydrogenated. The complete hydrogenation network is later studied. Our calculations reveal that while conversion to simpler molecules like HCN and HNC is indeed a possible outcome promoted by H-abstraction reactions, methylamine is also easily formed (CH3NH2). In fact, the stability of methylamine against hydrogen abstraction makes this molecule the preferred product of the reaction network. Our results serve as a stepping stone toward the accurate modeling of C-addition reactions in realistic astrochemical kinetic models.
Calcium Chemistry in Carbon-rich Circumstellar Environments: The Laboratory and Astronomical Discovery of Calcium Dicarbide, CaC2
Authors: Gupta, H.; Changala, P. B.; Cernicharo, J.; Pardo, J. R.; Agundez, M.; Cabezas, C.; Tercero, B.; Guelin, M.; McCarthy, M. C.
Journal: ASTROPHYSICAL JOURNAL LETTERS
Publication date: 2024/05/01
Abstract: Calcium dicarbide, CaC2, has been characterized at high resolution in the laboratory, and its main isotopologue, (CaC2)-Ca-40, has been assigned to 14 rotational emission lines between 14 and 115 GHz, including 12 previously unassigned lines, in the expanding molecular envelope of the evolved carbon star IRC+10216. Aided by high-level quantum calculations and measurements of multiple isotopologues, CaC2 is determined to be a T-shaped molecule with a highly ionic bond linking the metal atom to the C-2 unit, very similar in structure to isovalent magnesium dicarbide (MgC2). The excitation of CaC2 is characterized by a very low rotational temperature of 5.8 +/- 0.6 K and a kinetic temperature of 36 +/- 16 K, similar to values derived for MgC2. On the assumption that the emission originates from a 30 ” shell in IRC+10216, the column density of CaC2 is (5.6 +/- 1.7) x 10(11) cm(-2). CaC2 is only the second Ca-bearing molecule besides CaNC and only the second metal dicarbide besides MgC2 identified in space. Owing to the similarity between the predicted ion-molecule chemistry of Ca and Mg, a comparison of the CaC2 abundance with that of MgC2 and related species permits empirical inferences about the radiative association-dissociative recombination processes postulated to yield metal-bearing molecules in IRC+10216 and similar objects.
The magnetic field in the Flame nebula
Authors: Beslic, I.; Coude, S.; Lis, D. C.; Gerin, M.; Goldsmith, P. F.; Pety, J.; Roueff, A.; Demyk, K.; Dowell, C. D.; Einig, L.; Goicoechea, J. R.; Levrier, F.; Orkisz, J.; Peretto, N.; Santa-Maria, M. G.; Ysard, N.; Zakardjian, A.
Journal: ASTRONOMY & ASTROPHYSICS
Publication date: 2024/04/29
DOI: 10.1051/0004-6361/202348376
Abstract: Context. Star formation drives the evolution of galaxies and the cycling of matter between different phases of the interstellar medium and stars. The support of interstellar clouds against gravitational collapse by magnetic fields has been proposed as a possible explanation for the low observed star formation efficiency in galaxies and the Milky Way. The Planck satellite provided the first all-sky map of the magnetic field geometry in the diffuse interstellar medium on angular scales of 5-15 ‘. However, higher spatial resolution observations are required to understand the transition from diffuse, subcritical gas to dense, gravitationally unstable filaments. Aims. NGC 2024, also known as the Flame nebula, is located in the nearby Orion B molecular cloud. It contains a young, expanding H II region and a dense supercritical filament. This filament harbors embedded protostellar objects and is likely not supported by the magnetic field against gravitational collapse. Therefore, NGC 2024 provides an excellent opportunity to study the role of magnetic fields in the formation, evolution, and collapse of dense filaments, the dynamics of young H II regions, and the effects of mechanical and radiative feedback from massive stars on the surrounding molecular gas. Methods. We combined new 154 and 216 mu m dust polarization measurements carried out using the HAWC+ instrument aboard SOFIA with molecular line observations of (CN)-C-12(1-0) and HCO+(1-0) from the IRAM 30-m telescope to determine the magnetic field geometry, and to estimate the plane of the sky magnetic field strength across the NGC 2024 H II region and the surrounding molecular cloud. Results. The HAWC+ observations show an ordered magnetic field geometry in NGC 2024 that follows the morphology of the expanding H II region and the direction of the main dense filament. The derived plane of the sky magnetic field strength is moderate, ranging from 30 to 80 mu G. The strongest magnetic field is found at the eastern edge of the H II region, characterized by the highest gas densities and molecular line widths. In contrast, the weakest field is found toward the main, dense filament in NGC 2024. Conclusions. We find that the magnetic field has a non-negligible influence on the gas stability at the edges of the expanding H II shell (gas impacted by stellar feedback) and the filament (site of current star formation).
Quantum Optimization Methods for Satellite Mission Planning
Authors: Makarov, Anton; Perez-Herradon, Carlos; Franceschetto, Giacomo; Taddei, Marcio M.; Osaba, Eneko; del Barrio Cabello, Paloma; Villar-Rodriguez, Esther; Oregi, Izaskun
Journal: IEEE ACCESS
Publication date: 2024/04/08
DOI: 10.1109/ACCESS.2024.3402990
Abstract: Satellite mission planning for Earth observation satellites is a combinatorial optimization problem that consists of selecting the optimal subset of imaging requests, subject to constraints, to be fulfilled during an orbit pass of a satellite. The ever-growing amount of satellites in orbit underscores the need to operate them efficiently, which requires solving many instances of the problem in short periods of time. However, current classical algorithms often fail to find the global optimum or take too long to execute. Here, we approach the problem from a quantum computing point of view, which offers a promising alternative that could lead to significant improvements in solution quality or execution speed in the future. To this end, we study a planning problem with a variety of intricate constraints and discuss methods to encode them for quantum computers. Additionally, we experimentally assess the performance of quantum annealing and the quantum approximate optimization algorithm on a realistic and diverse dataset. Our results identify key aspects like graph connectivity and constraint structure that influence the performance of the methods. We explore the limits of today’s quantum algorithms and hardware, providing bounds on the problems that can be currently solved successfully and showing how the solution degrades as the complexity grows. This work aims to serve as a baseline for further research in the field and establish realistic expectations on current quantum optimization capabilities.
ALMA reveals a compact and massive molecular outflow driven by the young AGN in a nearby ULIRG
Authors: Holden, Luke R.; Tadhunter, Clive; Audibert, Anelise; Oosterloo, Tom; Almeida, Cristina Ramos; Morganti, Raffaella; Pereira-Santaella, Miguel; Lamperti, Isabella
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Publication date: 2024/04/05
Abstract: The ultraluminous infrared galaxy F13451+1232 is an excellent example of a galaxy merger in the early stages of active galactic nucleus (AGN) activity, a phase in which AGN-driven outflows are expected to be particularly important. However, previous observations have determined that the mass outflow rates of the warm ionized and neutral gas phases in F13451+1232 are relatively modest, and there has been no robust detection of molecular outflows. Using high-spatial resolution Atacama Large Millimeter/submillimeter Array CO(1-0) observations, we detect a kiloparsec-scale circumnuclear disc, as well as extended (r similar to 440 pc), intermediate-velocity (300 < |v| < 400 km s(-1)) cold molecular gas emission that cannot be explained by rotational disc motions. If interpreted as AGN-driven outflows, the mass outflow rates associated with this intermediate-velocity gas are relatively modest ((M) over dot(out) = 22-27 M-circle dot yr(-1)); however, we also detect a compact (r(out) < 120 pc), high-velocity (400 < v < 680 km s(-1)) cold molecular outflow near the primary nucleus of F13451+1232, which carries an order of magnitude more mass ((M) over dot(out) similar to 230 M-circle dot yr(-1)) than (and several times the kinetic power of) the previously detected warmer phases. Moreover, the similar spatial scales of this compact outflow and the radio structure indicate that it is likely accelerated by the small-scale (r similar to 130 pc) AGN jet in the primary nucleus of F13451+1232. Considering the compactness of the nuclear outflow and intermediate-velocity non-rotating gas that we detect, we argue that high-spatial resolution observations are necessary to properly quantify the properties of AGN-driven outflows and their impacts on host galaxies.
Accurate solution of the Index Tracking problem with a hybrid simulated annealing algorithm
Authors: Rubio-Garcia, Alvaro; Fernandez-Lorenzo, Samuel; Garcia-Ripoll, Juan Jose; Porras, Diego
Journal: PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
Publication date: 2024/04/01
DOI: 10.1016/j.physa.2024.129637
Abstract: An actively managed portfolio almost never beats the market in the long term. Thus, many investors often resort to passively managed portfolios whose aim is to follow a certain financial index. The task of building such passive portfolios aiming also to minimize the transaction costs is called Index Tracking (IT), where the goal is to track the index by holding only a small subset of assets in the index. As such, it is an NP-hard problem and becomes unfeasible to solve exactly for indices with more than 100 assets. In this work, we present a novel hybrid simulated annealing method that can efficiently solve the IT problem for large indices and is flexible enough to adapt to financially relevant constraints. By tracking the S&P-500 index between the years 2011 and 2018 we show that our algorithm is capable of finding optimal solutions in the in-sample period of past returns and can be tuned to provide optimal returns in the out-of-sample period of future returns. Finally, we focus on the task of holding an IT portfolio during one year and rebalancing the portfolio every month. Here, our hybrid simulated annealing algorithm is capable of producing financially optimal portfolios already for small subsets of assets and using reasonable computational resources, making it an appropriate tool for financial managers.
Avoiding barren plateaus in the variational determination of geometric entanglement
Authors: Zambrano, L.; Munoz-Moller, A. D.; Munoz, M.; Pereira, L.; Delgado, A.
Journal: QUANTUM SCIENCE AND TECHNOLOGY
Publication date: 2024/03/28
Abstract: The barren plateau (BP) phenomenon is one of the main obstacles to implementing variational quantum algorithms in the current generation of quantum processors. Here, we introduce a method capable of avoiding the BP phenomenon in the variational determination of the geometric measure of entanglement for a large number of qubits. The method is based on measuring compatible two-qubit local functions whose optimization allows for achieving a well-suited initial condition from which a global function can be further optimized without encountering a BP. We analytically demonstrate that the local functions can be efficiently estimated and optimized. Numerical simulations up to 18 qubit GHZ and W states demonstrate that the method converges to the exact value. In particular, the method allows for escaping from BPs induced by hardware noise or global functions defined on high-dimensional systems. Numerical simulations with noise agree with experiments carried out on IBM’s quantum processors for seven qubits.
AutoQML: Automatic generation and training of robust quantum-inspired classifiers by using evolutionary algorithms on grayscale images
Authors: Altares-Lopez, Sergio; Garcia-Ripoll, Juan Jose; Ribeiro, Angela
Journal: EXPERT SYSTEMS WITH APPLICATIONS
Publication date: 2024/03/25
DOI: 10.1016/j.eswa.2023.122984
Abstract: A new hybrid system is proposed for automatically generating and training quantum-inspired classifiers on grayscale images by using multiobjective genetic algorithms. It is defined a dynamic fitness function to obtain the smallest circuit complexity and highest accuracy on unseen data, ensuring that the proposed technique is generalizable and robust. At the same time, it is minimized the complexity of the generated circuits in terms of the number of entangling operators by penalizing their appearance and number of gates. The size of the images is reduced by using two dimensionality reduction approaches: principal component analysis (PCA), which is encoded within the individual and genetically optimized by the system, and a small convolutional autoencoder (CAE). These two methods are compared with one another and with a classical nonlinear approach to understand their behaviors and to ensure that the classification ability is due to the quantum circuit and not the preprocessing technique used for dimensionality reduction.
Photonic quantum metrology with variational quantum optical nonlinearities
Authors: de las Heras, A. Munoz; Tabares, C.; Schneider, J. T.; Tagliacozzo, L.; Porras, D.; Gonzalez-Tudela, A.
Journal: PHYSICAL REVIEW RESEARCH
Publication date: 2024/03/19
DOI: 10.1103/PhysRevResearch.6.013299
Abstract: Photonic quantum metrology harnesses quantum states of light, such as NOON or twin-Fock states, to measure unknown parameters beyond classical precision limits. Current protocols suffer from two severe limitations that preclude their scalability: the exponential decrease in fidelities (or probabilities) when generating states with large photon numbers due to gate errors and the increased sensitivity of such states to noise. Here, we develop a deterministic protocol combining quantum optical nonlinearities and variational quantum algorithms that provides a substantial improvement on both fronts. First, we show how the variational protocol can generate metrologically relevant states with a small number of operations which do not significantly depend on photon number, resulting in exponential improvements in fidelities when gate errors are considered. Second, we show that such states offer a better robustness to noise compared to other states in the literature. Since our protocol harnesses interactions already appearing in state-of-the-art setups, such as cavity QED, we expect that it will lead to more scalable photonic quantum metrology in the near future.
Hyperfine excitation of NH and ND by molecular hydrogen Rate coefficients and astrophysical modeling
Authors: Jankowiak, Paul Pirlot; Lique, Francois; Goicoechea, Javier R.
Journal: ASTRONOMY & ASTROPHYSICS
Publication date: 2024/03/15
DOI: 10.1051/0004-6361/202348865
Abstract: The NH and ND radicals are of key importance in the comprehension of nitrogen chemistry and the enhancement of deuterated molecules in the interstellar medium. Observations by space telescopes yield spectra that can resolve the fine and hyperfine structure of these radicals, a consequence of the electronic and magnetic interactions of nitrogen, hydrogen, and deuterium nuclei. Accurate rate coefficients, induced by collisions with H-2, are required to interpret spectra of these radicals. We report the first rate coefficients for fine and hyperfine transitions of NH and ND in collision with both ortho- and para-H-2. Based on a recent four-dimensional potential energy surface, fine-structure resolved cross sections and rate coefficients are computed with the time-independent close-coupling method over a temperature range of 5-300 K. Our calculations include the first 25 energy levels of NH and ND. Hyperfine resolved cross sections and rate coefficients are determined using the infinite-order sudden (IOS) approximation between 5 and 200 K for NH and 100 K for ND. We consider the first 71 and 105 energy levels of NH and ND, respectively. General propensity rules are discussed. We found a significant isotopic substitution effect in the rate coefficients. In addition, the rate coefficients for collisions with H-2 are larger than those with He by a factor of up to 5, leading to lower critical densities for collisional excitation with H-2 than He. The impact of the new set of collisional data has been investigated in simple radiative transfer models of the NH emission seen toward the Orion Bar and the ejecta of the eta Carinae binary star. We observed significant differences by a factor of 5 between the presently determined column densities for NH compared to those from the literature using He as a collider.
Exploring Quantum Annealing Architectures: A Spin Glass Perspective
Authors: Jauma, Gabriel; Garcia-Ripoll, Juan Jose; Pino, Manuel
Journal: ADVANCED QUANTUM TECHNOLOGIES
Publication date: 2024/03/14
Abstract: This work analyzes the spin-glass transition across various Ising models relevant to quantum annealers. By employing the parallel tempering method, the location of the spin-glass phase transition is extrapolated from the pseudo-critical temperature of finite-sized systems. The results confirm a spin-glass phase at finite temperature in random-regular and small-world graphs, in agreement with previous studies. However, strong evidence is obtained that this phase only occurs at zero temperature in the quasi-2D graphs of D-Wave, as their pseudo-critical temperature drifts toward zero. This implies that the asymptotic runtime to find the low-energy configuration of those graphs is likely to be polynomial in the size of the problem. Nevertheless, this scaling may only be reached for system sizes much larger than existing annealers, as the drift in the pseudo-critical temperature is slow. This slowness, together with an abrupt increase in thermalization times around the pseudo-critical temperature, may render the search for low-energy configurations with classical methods impractical. The search for quantum advantage with quantum annealers requires finding families of problems in which classical methods fail, leaving room for improvement. In search of these families and their characteristics, Ising problems with the topologies of D-Wave’s annealers are studied and a dichotomy is reconciled: in theory, they should be easy, but in practice, they are hard. image
Numerical simulation of large-scale nonlinear open quantum mechanics
Authors: Roda-Llordes, M.; Candoli, D.; Grochowski, P. T.; Riera-Campeny, A.; Agrenius, T.; Garcia-Ripoll, J. J.; Gonzalez-Ballestero, C.; Romero-Isart, O.
Journal: PHYSICAL REVIEW RESEARCH
Publication date: 2024/03/08
DOI: 10.1103/PhysRevResearch.6.013262
Abstract: We introduce a method to solve nonlinear open quantum dynamics of a particle in situations where its state undergoes significant expansion in phase space while generating small quantum features at the phase-space Planck scale. Our approach involves simulating two steps. First, we transform the Wigner function into a timedependent frame that leverages information from the classical trajectory to efficiently represent the quantum state in phase space. Next, we simulate the dynamics in this frame using a numerical method that implements this time-dependent nonlinear change of variables. To demonstrate the capabilities of our method, we examine the open quantum dynamics of a particle evolving in a one-dimensional weak quartic potential after initially being ground-state cooled in a tight harmonic potential. This approach is particularly relevant to ongoing efforts to design, optimize, and understand experiments targeting the preparation of macroscopic quantum superposition states of massive particles through nonlinear quantum dynamics.
Converting Long-Range Entanglement into Mixture: Tensor-Network Approach to Local Equilibration
Authors: Frias-Perez, Miguel; Tagliacozzo, Luca; Banuls, Mari Carmen
Journal: PHYSICAL REVIEW LETTERS
Publication date: 2024/03/08
DOI: 10.1103/PhysRevLett.132.100402
Abstract: In the out-of-equilibrium evolution induced by a quench, fast degrees of freedom generate long-range entanglement that is hard to encode with standard tensor networks. However, local observables only sense such long-range correlations through their contribution to the reduced local state as a mixture. We present a tensor network method that identifies such long-range entanglement and efficiently transforms it into mixture, much easier to represent. In this way, we obtain an effective description of the time-evolved state as a density matrix that captures the long-time behavior of local operators with finite computational resources.
Experimental and theoretical assessment of the enhanced hydrogen adsorption on polycyclic aromatic hydrocarbons upon decoration with alkali metals
Authors: Reider, Anna Maria; Kollotzek, Siegfried; Scheier, Paul; Calvo, Florent; Yurtsever, Ersin; Pirani, Fernando; Bartolomei, Massimiliano; Hernandez, Marta I.; Gonzalez-Lezana, Tomas; Campos-Martinez, Jose
Journal: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Publication date: 2024/03/08
DOI: 10.1016/j.ijhydene.2024.01.244
Abstract: Hydrogen storage by physisorption on carbon-based materials is limited by comparatively low adsorption energies. However, decoration of the carbon substrate with alkali, alkaline earth, or other metal atoms has been proposed as a means to enhance adsorption energies. The decoration affects also the stability of these materials since it makes them more stable and resilient in the repeated cycles of charge and discharge that would be required for a good material devoted to storage. We investigate hydrogen storage capacities of small polycyclic aromatic hydrocarbons (PAHs) cations grown in ultracold helium nanodroplets by analyzing the ion abundances and stabilities. The observations are assessed with quantum chemical calculations and atomistic simulations. It is experimentally shown that the addition of an alkali ion significantly enhances the hydrogen adsorption of the studied PAHs, up to 25% over the bare PAH in the experimental conditions studied here, and the simulations confirm this general trend except for some minor residual discrepancies in the special stabilities (magic numbers). Several approaches to study larger and different PAH compounds are also proposed, and for all cases it is found that alkali decoration increases energy stability by more than 100%.
Peeling back the layers of extinction of dusty galaxies in the era of JWST: modelling joint NIRSpec plus MIRI spectra at rest-frame 1.5-28 ?m
Authors: Donnan, F. R.; Garcia-Bernete, I; Rigopoulou, D.; Pereira-Santaella, M.; Roche, P. F.; Alonso-Herrero, A.
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Publication date: 2024/03/06
Abstract: We present an analysis of the combined NIRSpec and MIRI spectra of dusty galaxies between 1.5 and 28 mu m rest-frame by implementing a differential extinction model, where the strength of extinction varies across the spectrum as different layers of the obscuring dust are probed. Our model is able to recover a 2D distribution of dust temperature and extinction, which allows inference of the physical nature of the dust in these environments. We show that differential extinction is necessary to reproduce the spectra of four highly obscured Luminous Infrared Galaxies observed with NIRSpec IFU and MIRI MRS, where simple screen or uniformly mixed dust distributions fail to fit the data. We additionally compare the extinction of H ii regions in these galaxies via hydrogen recombination lines, the extinction of molecular gas via the H-2 lines, polycyclic aromatic hydrocarbons via the 12.7/11.3 PAH ratio and the stellar continuum. We find that the molecular gas is deeply buried with the H ii regions in star-forming regions, with a similar extinction to the hottest dust components. However, we find the cooler dust to be less obscured, at a similar extinction to the stellar continuum and PAHs. The nuclei show a complex dust distribution with VV114 NE, NGC 3256 S, and IIZw96 SW, showing a deeply buried continuum source relative to the molecular gas/H ii regions. Additionally, NGC 3256 S, NGC 7469, and VV114 SW show an isolated hot dust component, indicative of AGN heating, where NGC 3256 S and NGC 7469 are previously known as AGN.