Publications (2025)
Quantum-classical rate coefficients for O2 + N2 inelastic collisions with very high vibrational levels
Authors: Yang, Jiawei; Hong, Qizhen; Bartolomei, Massimiliano; Pirani, Fernando; Coletti, Cecilia; Sun, Quanhua; Li, Jun
Journal: PHYSICAL REVIEW A
Publication date: 2025/03/06
DOI: 10.1103/PhysRevA.111.032804
Abstract: Energy exchanges among internal energy modes in O2 + N2 collisions directly affect the microscopic dynamical evolution of nonequilibrium phenomena in these gases. Quantum calculations of energy exchanges, especially those involving high molecular levels, are challenging due to their daunting computational costs. In this study, by capturing quantum effects associated with vibrational motions, we employ the improved mixed quantum-classical (MQC) method to obtain rate coefficients of both vibration-to-vibration (V-V) and vibrationto-translation or rotation (V-T-R) energy exchanges for O2 + N2 collisions over a wide temperature range (100-9000 K). This approach permits the achievement of results up to vibrational levels close to the molecular dissociation limit. The adopted potential-energy surface (PES) is formulated using a proper representation of both intermolecular and intramolecular components to provide the dependence of the interaction energy on molecular separation distances and molecular deformations. Notably, the MQC calculations with the new PES yield vibrational relaxation rate coefficients consistent with experimental data. In addition to the comprehensive MQC data, we utilize Gaussian process regression to predict rates for processes not directly computed, thus completing the V-V and V-T-R datasets for selected processes across full vibrational levels of O2 and N2. At low temperatures, notable anti-Arrhenius behavior is observed, which would enhance relaxation processes in cold environments typical of upper and planetary atmospheres. The extensive datasets are valuable for describing the kinetic behaviors of O2 and N2 across various vibrational levels and temperatures, aiding in addressing non-local thermodynamic equilibrium conditions where the influence of vibrationally excited air molecules cannot be ignored.
Pauli weight requirement of the matrix elements in time-evolved local operators: Dependence beyond the equilibration temperature
Authors: Ramos-Marimon, Carlos; Carignano, Stefano; Tagliacozzo, Luca
Journal: PHYSICAL REVIEW B
Publication date: 2025/03/05
DOI: 10.1103/PhysRevB.111.094301
Abstract: The complexity of simulating the out-of-equilibrium evolution of local operators in the Heisenberg picture is governed by the operator entanglement, which grows linearly in time for generic nonintegrable systems, leading to an exponential increase in computational resources. A promising approach to simplify this challenge involves discarding parts of the operator and focusing on a subspace formed by light Pauli strings-strings with few Pauli matrices-as proposed by Rakovszki et al. [Phys. Rev. B 105, 075131 (2022)]. In this work, we investigate whether this strategy can be applied to quenches starting from homogeneous product states. For ergodic dynamics, these initial states grant access to a wide range of equilibration temperatures. By concentrating on the desired matrix elements and retaining only the portion of the operator that contains Pauli strings parallel to the initial state, we uncover a complex scenario. In some cases, the light Pauli strings suffice to describe the dynamics, enabling efficient simulation with current algorithms. However, in other cases, heavier strings become necessary, pushing computational demands beyond our current capabilities. We analyze this behavior by introducing a measure of complexity, the operator weight entropy, which we compute for different operators across most points on the Bloch sphere.
Passive Photonic CZ Gate with Two-Level Emitters in Chiral Multimode Waveguide QED
Authors: Levy-Yeyati, Tomas; Vega, Carlos; Ramos, Tomas; Gonzalez-Tudela, Alejandro
Journal: PRX QUANTUM
Publication date: 2025/03/05
DOI: 10.1103/PRXQuantum.6.010342
Abstract: Engineering deterministic photonic gates with simple resources is one of the long-standing challenges in photonic quantum computing. Here, we design a passive conditional gate between copropagating photons using an array of only two-level emitters. The key resource is to harness the effective photon-photon interaction induced by the chiral coupling of the emitter array to two waveguide modes with different resonant momenta at the emitter’s transition frequency. By studying the system’s multiphoton scattering response, we demonstrate that, in certain limits, this configuration induces a nonlinear yr-phase shift between the polariton eigenstates of the system without distorting spectrally the wave packets. Then, we show how to harness this nonlinear phase shift to engineer a conditional, deterministic photonic gate in different qubit encodings, with a fidelity arbitrarily close to 1 in the limit of large number of emitters and coupling efficiency. Our configuration can be implemented in topological photonic setups with multiple chiral-edge modes, opening their use for quantum information processing, or in other setups where such chiral light-matter couplings can be effectively obtained, such as optical fibers or photonic-crystal optical and microwave waveguides.
Low crosstalk modular flip-chip architecture for coupled superconducting qubits
Authors: Ihssen, Soeren; Geisert, Simon; Jauma, Gabriel; Winkel, Patrick; Spiecker, Martin; Zapata, Nicolas; Gosling, Nicolas; Paluch, Patrick; Pino, Manuel; Reisinger, Thomas; Wernsdorfer, Wolfgang; Garcia-Ripoll, Juan Jose; Pop, Ioan M.
Journal: APPLIED PHYSICS LETTERS
Publication date: 2025/03/01
DOI: 10.1063/5.0245667
Abstract: We present a flip-chip architecture for an array of coupled superconducting qubits, in which circuit components reside inside individual microwave enclosures. In contrast to other flip-chip approaches, the qubit chips in our architecture are electrically floating, which guarantees a simple, fully modular assembly of capacitively coupled circuit components, such as qubit, control, and coupling structures as well as reduced crosstalk between the components. We validate the concept with a chain of three nearest neighbor coupled generalized flux qubits in which the center qubit acts as a frequency-tunable coupler. Using this coupler, we demonstrate a transverse coupling on/off ratio approximate to 50, zz-crosstalk approximate to 0.7 kHz between resonant qubits and isolation between the qubit enclosures >60 dB.
MADWAVE3: A quantum time dependent wave packet code for nonadiabatic state-to-state reaction dynamics of triatomic systems
Authors: Roncero, Octavio; del Mazo-Sevillano, Pablo
Journal: COMPUTER PHYSICS COMMUNICATIONS
Publication date: 2025/03/01
DOI: 10.1016/j.cpc.2024.109471
Abstract: We present MADWAVE3, a FORTRAN90 code designed for quantum time-dependent wave packet propagation in triatomic systems. This program allows the calculation of state-to-state probabilities for inelastic and reactive collisions, as well as photodissociation processes, over one or multiple coupled diabatic electronic states. The code is highly parallelized using MPI and OpenMP. The execution requires the potential energy surfaces of the different electronic states involved, as well as the transition dipole moments for photodissociation processes. The formalism underlying the code is presented in section 2, together with the modular structure of the code. This is followed by the installation procedures and a comprehensive list and explanation of the parameters that control the code, organized within their respective namelists. Finally, a case study is presented, focusing on the prototypical reactive collision H +DH(v, j)- H2(v ‘, j ‘ ) + D. Both the potential energy surface and the input files required to reproduce the calculation are provided and are available on the repository’s main page. This example is used to study the parallelization speedup of the code.
Electron Scattering Cross Sections from Thiazole for Impact Energies Ranging from 1 to 1000 eV
Authors: Garcia-Abenza, Adrian; Lozano, Ana I.; Oller, Juan C.; Rosado, Jaime; Blanco, Francisco; Limao-Vieira, Paulo; Garcia, Gustavo
Journal: MOLECULES
Publication date: 2025/03/01
DOI: 10.3390/molecules30051097
Abstract: Total electron scattering cross sections (TCSs), in the energy range of 1-100 eV, have been measured with a high-resolution magnetically confined electron transmission apparatus, with total uncertainty limits estimated to be within +/- 5%. No previous experimental TCS data have been found for comparison. Electron attachment resonances, corresponding to transient negative ion formation, have been identified for energies below 20 eV by analyzing their contribution to the measured local maxima of the TCSs. Most of these resonances were observed for the first time. By means of our screening-corrected additivity rule (including interference effects) calculation method (IAM-SCAR + I), we extended TCS values to up to 1000 eV. This method also provides integral elastic, electronic excitation, and ionization cross sections for impact energies above 20 eV with total uncertainties of about +/- 10%. Comparisons, where possible, of the present electron scattering values with other values available in the literature are given.
Electron Attachment to Nitric Oxide (NO) Controversy
Authors: Lozano, Ana I.; Oller, Juan C.; Limao-Vieira, Paulo; Garcia, Gustavo
Journal: JOURNAL OF PHYSICAL CHEMISTRY A
Publication date: 2025/02/28
Abstract: We report novel total electron scattering cross sections (TCS) from nitric oxide (NO) in the impact energy range from 1 to 15 eV by using a magnetically confined electron transmission apparatus. The accuracy of the data to within 5% and its consistency across the energy range investigated, shows significant discrepancies from previous works as to the major resonance features and magnitude of the TCS. Within the shape of the TCS, we have identified nine features which have been assigned to electron attachment resonances, most of them reported for the first time, while a comprehensive analysis of those peaking at 7.0, 7.8, and 8.8 eV has led to solve the controversy about dissociative electron attachment (DEA) cross-section that persisted for more than 50 years.
Hydrogenation of acetaldehyde on interstellar ice analogs results in limited destruction
Authors: Molpeceres, G.; Nguyen, T.; Oba, Y.; Watanabe, N.
Journal: ASTRONOMY & ASTROPHYSICS
Publication date: 2025/02/20
DOI: 10.1051/0004-6361/202451990
Abstract: Context. Acetaldehyde (CH3CHO) is one of the most abundant interstellar complex organic molecules and its hydrogenation has important implications in several fundamental processes of interstellar chemistry, such as deuterium fractionation, reactive desorption, or the relation between organic functional groups of detected molecules. Aims. We seek to determine what the main hydrogenation paths of CH3CHO are. As a partially unsaturated molecule, CH3CHO can have links with more hydrogenated species, such as ethanol (C2H5OH), or with more unsaturated ones, such as ketene (H2CCO). Methods. We used highly accurate quantum chemical calculations to determine the reaction rate constants for the CH3CHO + H/D reaction. We later studied, using more approximated methods, the fate of the majoritarian product of the reaction, the acetyl radical CH3CO after subsequent reaction with hydrogen or deuterium atoms. Our theoretical results were tested with our experiments on the hydrogenation and deuteration of CH3CHO ice. Results. We find that acetaldehyde resists hydrogenation, with only a 10% of conversion to products different than CH3CHO. This is due to a predominance of H abstraction at the HCO moiety, with reaction rate constants up to four orders of magnitude higher than the next possible reaction channel, which is hydrogenation at the aldehydic carbon. The formed CH3CO radical experiences barrierless or nearly barrierless reactions in all possible reaction positions, reforming CH3CHO and creating a closed loop that protects the molecule against hydrogenation. We constrained the branching ratios for the second reaction from the experiments. Our experiments agree with the calculations and from the combination of both we can explain the presence of H2CCO, CO, CH4, C2H5OH, H2CO, or CH3OH as minor products at the end of the reaction. We provide recommendations for future modeling efforts. Conclusions. Our results show limited destruction of acetaldehyde, reinforcing the vision of this molecule as an abundant and resilient COM. From the experiments, we are not able to observe the reactive desorption of this molecule. Our results align with other modeling works, showing that the link between CH3CHO and C2H5OH is not direct. Finally, our results can explain the excess of CH3CDO found in prestellar cores.
Improving quantum metrology protocols with programmable photonic circuits
Authors: de las Heras, Alberto Munoz; Porras, Diego; Gonzalez-Tudela, Alejandro
Journal: NANOPHOTONICS
Publication date: 2025/02/20
Abstract: Photonic quantum metrology enables the measurement of physical parameters with precision surpassing classical limits by using quantum states of light. However, generating states providing a large metrological advantage is hard because standard probabilistic methods suffer from low generation rates. Deterministic protocols using non-linear interactions offer a path to overcome this problem, but they are currently limited by the errors introduced during the interaction time. Thus, finding strategies to minimize the interaction time of these non-linearities is still a relevant question. In this work, we introduce and compare different deterministic strategies based on continuous and programmable Jaynes-Cummings and Kerr-type interactions, aiming to maximize the metrological advantage while minimizing the interaction time. We find that programmable interactions provide a larger metrological advantage than continuous operations at the expense of slightly larger interaction times. We show that while for Jaynes-Cummings non-linearities the interaction time grows with the photon number, for Kerr-type ones it decreases, favoring the scalability to big photon numbers. Finally, we also optimize different measurement strategies for the deterministically generated states based on photon-counting and homodyne detection.
Validity condition for high-fidelity digitized quantum annealing
Authors: Santos, Alan C.
Journal: PHYSICAL REVIEW A
Publication date: 2025/02/18
DOI: 10.1103/PhysRevA.111.022618
Abstract: Digitizing an adiabatic evolution is a strategy able to combine the good performance of gate-based quantum processors with the advantages of adiabatic algorithms, thus providing a hybrid model for efficient quantum information processing. In this work we develop validity conditions for high-fidelity digital adiabatic tasks. To this end, we assume a digitizing process based on the Suzuki-Trotter decomposition, which allows us to introduce a digitized adiabatic theorem. As a consequence of this theorem, we show that the performance of such a hybrid model is limited by the fundamental constraints on the adiabatic theorem validity, even in ideal quantum processors. We argue how our approach predicts the existence of intrinsic nonadiabatic errors reported by Barends et al. [Nature (London) 534, 222 (2016)] through an empirical study of digital annealing. In addition, our approach allows us to explain the existence of a scaling of the number of Suzuki-Trotter blocks for the optimal digital circuit with respect to the optimal adiabatic total evolution time, as reported by Mbeng et al. [Phys. Rev. B 100, 224201 (2019)] through robust numerical analysis of digital annealing. We illustrate our results through two examples of digitized adiabatic algorithms, namely, the two-qubit exact-cover problem and the three-qubit adiabatic factorization of the number 21.
Bound polariton states in the Dicke-Ising model
Authors: Roman-Roche, Juan; Gomez-Leon, Alvaro; Luis, Fernando; Zueco, David
Journal: NANOPHOTONICS
Publication date: 2025/02/17
Abstract: We present a study of hybrid light-matter excitations in cavity QED materials using the Dicke-Ising model as a theoretical framework. Leveraging linear response theory, we derive the exact excitations of the system in the thermodynamic limit. Our results demonstrate that the cavity can localize spin excitations, leading to the formation of bound polaritons, where the cavity acts as an impurity of the two-excitation band, localizing spin-wave pairs around single-spin domains. We derive the condition for the existence of these bound states and discuss its satisfiability in different regimes. Finally, we show that these effects persist in finite systems using exact-diagonalization calculations.
Validation of millimetre and sub-millimetre atmospheric collision-induced absorption at Chajnantor
Authors: Pardo, J. R.; De Breuck, C.; Muders, D.; Gonzalez, J.; Perez-Beaupuits, J. P.; Cernicharo, J.; Prigent, C.; Serabyn, E.; Montenegro-Montes, F. M.; Mroczkowski, T.; Phillips, N.; Villard, E.
Journal: ASTRONOMY & ASTROPHYSICS
Publication date: 2025/02/13
DOI: 10.1051/0004-6361/202452159
Abstract: Due to the importance of a reference atmospheric radiative transfer model for both planning and calibrating ground-based observations at millimetre and sub-millimetre wavelengths, we have undertaken a validation campaign consisting of acquiring atmospheric spectra under different weather conditions, in different diurnal moments and seasons, with the Atacama Pathfinder EXperiment (APEX), due to the excellent stability of its receivers and the very high frequency resolution of its back-ends. As a result, a dataset consisting of 56 spectra within the 157.3-742.1 GHz frequency range, at kilohertz resolution (smoothed to similar to 2-10 MHz for analysis), and spanning one order of magnitude (similar to 0.35-3.5 mm) in precipitable water vapour columns, has been gathered from October 2020 to September 2022. These data are unique for their quality and completeness and, due to the proximity of APEX to the Atacama Large Millimeter/Submillimeter Array (ALMA), they provide an excellent opportunity to validate the atmospheric radiative transfer model currently installed in the ALMA software. The main issues addressed in the study are possible missing lines in the model, line shapes, vertical profiles of atmospheric physical parameters and molecular abundances, seasonal and diurnal variations, and collision-induced absorption (CIA), to which this paper is devoted, in its N-2-N-2 + N-2-O-2 + O-2-O-2 (dry) and N-2-H2O + O-2 -H2O (‘foreign’ wet) mechanisms. All these CIA terms should remain unchanged in the above-mentioned ALMA atmospheric model as a result of this work.
Quantum Control of Resonance Lifetimes in Molecular Photodissociation with Intense Laser Fields
Authors: Garcia-Vela, Alberto
Journal: JOURNAL OF CHEMICAL THEORY AND COMPUTATION
Publication date: 2025/02/10
Abstract: Control of molecular reaction dynamics has been pursued in the last decades. Among these reactions are molecular photodissociation processes governed by resonances. Controlling the lifetime of such resonances imply to control the time duration of the processes. Here, some control schemes that apply moderately intense laser fields are proposed to modify (reducing or increasing) a resonance lifetime. The control strategy applies an intense field as a way to generate a new effective coupling that produces a resonance decay different from the natural one, with a different decay lifetime. In particular, different control schemes are suggested to reduce the lifetime of a long-lived resonance, and to increase the lifetime of a short-lived resonance. A large degree and flexibility of control both in the reduction and in the increase of the resonance lifetime is demonstrated. The experimental applicability of the schemes is discussed. The present schemes thus open the possibility of extensive and universal control of molecular photodissociation processes mediated by resonances.
Superoxide anion (O2-) collisions with CO2 molecules in the energy range of 50-950 eV
Authors: Guerra, C.; Leiferman, M.; Lozano, A. I.; Aguilar-Galindo, F.; Diaz-Tendero, S.; Oller, J. C.; Limao-Vieira, P.; Garcia, G.
Journal: JOURNAL OF CHEMICAL PHYSICS
Publication date: 2025/02/07
DOI: 10.1063/5.0242954
Abstract: A novel gas-phase molecular scattering study is reported for O-2(-) collisions with CO2 for impact energies ranging from 50 to 950 eV in the lab frame. The absolute total electron detachment, relative total, and partial ionization cross sections have been measured within this energy range together with the positive ion yields. The primary anionic beam projectile is produced in a pulsed hollow cathode discharge induced plasma, and its interactions with the neutral molecular target occur in a gas cell at a well-known constant pressure. For impact energies above 500 eV, high mass (m > 44 u) charged complexes have been detected. With the aid of a theoretical study using ab initio methods, we propose a mechanism to infer the formation of these cationic species, which have been assigned to projectile-target stable compounds (CO3+ and CO4+).
Light-matter correlations in Quantum Floquet engineering of cavity quantum materials
Authors: Perez-Gonzalez, Beatriz; Platero, Gloria; Gomez-Leon, Alvaro
Journal: QUANTUM
Publication date: 2025/02/06
Abstract: Quantum Floquet engineering (QFE) seeks to generalize the control of quantum systems with classical external fields, widely known as Semi-Classical Floquet engineering (SCFE), to quantum fields. However, to faithfully capture the physics at arbitrary coupling, a gauge-invariant description of light-matter interaction in cavity-QED materials is required, which makes the Hamiltonian highly non-linear in photonic operators. We provide a non-perturbative truncation scheme of the Hamiltonian, which is valid or arbitrary coupling strength, and use it to investigate the role of light-matter correlations, which are absent in SCFE. We find that even in the high-frequency regime, light- matter correlations can be crucial, in particular for the topological properties of a system. As an example, we show that for a SSH chain coupled to a cavity, light-matter correlations break the original chiral symmetry of the chain, strongly affecting the robustness of its edge states. In addition, we show how light-matter correlations are imprinted in the photonic spectral function and discuss their relation with the topology of the bands.