Maximum population transfer in a periodically driven two-level system

We study the dynamics of a two-level quantum system under the influence of sinusoidal driving in the intermediate frequency regime. Analyzing the Floquet quasienergy spectrum, we find combinations of the field parameters for which population transfer is optimal and takes place through a series of well defined steps of fixed duration. We also show how the corresponding evolution operator can be approximated at all times by a very simple analytical expression. We propose this model as being specially suitable for treating periodic driving at avoided crossings found in complex multi-level systems, and thus show a relevant application of our results to designing a control protocol in a realistic molecular modelComment: 7 pages, 6 figure

4U 1626-67 as seen by Suzaku before and after the 2008 torque reversal

Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. The main goal of the present work is to study this recent torque reversal that occurred in 2008 February. Methods. We present a spectral analysis of this source using two pointed observations performed by Suzaku in 2006 March and in 2010 September. Results. We confirm with Suzaku the presence of a strong emission-line complex centered on 1 keV, with the strongest line being the hydrogen-like Ne Ly-alpha at 1.025(3) keV. We were able to resolve this complex with up to seven emission lines. A dramatic increase of the intensity of the Ne Ly-alpha line after the 2008 torque reversal occurred, with the equivalent width of this line reaching almost the same value measured by ASCA in 1993. We also report on the detection of a cyclotron line feature centered at ~37 keV. In spite of the fact that an increase of the X-ray luminosity (0.5-100 keV) of a factor of ~2.8 occurred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the ~1 keV line complex increased by an overall factor of ~8. Conclusions. Our results favor a scenario in which the neutron star in 4U 1626-67 accretes material from a geometrically thin disk during both the spin-up and spin-down phases.Comment: 7 pages, 5 figures and 2 tables. Accepted in A&

Correspondence between classical and quantum resonances

Bifurcations take place in molecular Hamiltonian nonlinear systems as the excitation energy increases, leading to the appearance of different classical resonances. In this paper, we study the quantum manifestations of these classical resonances in the isomerizing system CN-Li Li-CN. By using a correlation diagram of eigenenergies versus Planck constant, we show the existence of different series of avoided crossings, leading to the corresponding series of quantum resonances, which represent the quantum manifestations of the classical resonances. Moreover, the extrapolation of these series to h = 0 unveils the correspondence between the bifurcation energy of classical resonances and the energy of the series of quantum resonances in the semiclassical limit → 0. Additionally, in order to obtain analytical expressions for our results, a semiclassical theory is develope

The Poincare-Birkhoff theorem in Quantum Mechanics

Quantum manifestations of the dynamics around resonant tori in perturbed Hamiltonian systems, dictated by the Poincar\'e--Birkhoff theorem, are shown to exist. They are embedded in the interactions involving states which differ in a number of quanta equal to the order of the classical resonance. Moreover, the associated classical phase space structures are mimicked in the quasiprobability density functions and their zeros.Comment: 5 pages, 3 figures, Full resolution figures available at http://www.df.uba.ar/users/wisniaki/publications.htm

Unraveling the highly nonlinear dynamics of KCN molecular system using Lagrangian descriptors

In this work, we identify the phase-space structures which are responsible for the chaotic dynamics observed in KCN molecular system using the Lagrangian descriptors. We show that the vibrational dynamics of this molecule is strongly determined by the invariant manifolds associated with a particular stretching periodic orbit previously described (Párraga et al., 2018). Likewise, the representation of these invariant manifolds on a Poincaré surface of section is also studied, concluding that the intricate depiction that is observed has its origin in the complex behavior of the manifolds, which is a consequence of the strong anharmonicities in the potential energy surfaceThis work has been partially supported by the Grants PID2021-122711NB-C21 and CEX2019-000904-S funded by MCIN/AEI/10.13039/501100011033, by the People Programme (Marie Curie Actions) of the European Union’s Horizon 2020 Research and Innovation Program under Grant No. 734557, and by the Comunidad de Madrid, Spain under the Grant APOYO-JOVENES-4L2UB6-53-29443N (GeoCoSiM) financed within the Plurianual Agreement with the Universidad Politécnica de Madrid, Spain in the line to improve the research of young doctor

The pre-outburst flare of the A 0535+26 August/September 2005 outburst

We study the spectral and temporal behavior of the High Mass X-ray Binary A 0535+26 during a `pre-outburst flare' which took place ~5 d before the peak of a normal (type I) outburst in August/September 2005. We compare the studied behavior with that observed during the outburst. We analyse RXTE observations that monitored A 0535+26 during the outburst. We complete spectral and timing analyses of the data. We study the evolution of the pulse period, present energy-dependent pulse profiles both at the initial pre-outburst flare and close to outburst maximum, and measure how the cyclotron resonance-scattering feature (hereafter CRSF) evolves. We present three main results: a constant period P=103.3960(5)s is measured until periastron passage, followed by a spin-up with a decreasing period derivative of Pdot=(-1.69+/-0.04)x10^(-8)s/s at MJD 53618, and P remains constant again at the end of the main outburst. The spin-up provides evidence for the existence of an accretion disk during the normal outburst. We measure a CRSF energy of Ecyc~50kev during the pre-outburst flare, and Ecyc~46kev during the main outburst. The pulse shape, which varies significantly during both pre-outburst flare and main outburst, evolves strongly with photon energy.Comment: 4 pages, 4 figures, accepted for publication in A&A Letters. To be published in parallel to Postnov et al. 200

Optimizing an APSP implementation for NVIDIA GPUs using kernel characterization criteria

Producción CientíficaDuring the last years, GPU manycore devices have demonstrated their usefulness to accelerate computationally intensive problems. Although arriving at a parallelization of a highly parallel algorithm is an affordable task, the optimization of GPU codes is a challenging activity. The main reason for this is the number of parameters, programming choices, and tuning techniques available, many of them related with complex and sometimes hidden architecture details. A useful strategy to systematically attack these optimization problems is to characterize the different kernels of the application, and use this knowledge to select appropriate configuration parameters. The All-Pair Shortest-Path (APSP) problem is a well-known problem in graph theory whose objective is to find the shortest paths between any pairs of nodes in a graph. This problem can be solved by highly parallel and computational intensive tasks, being a good candidate to be exploited by manycore devices. In this paper, we use kernel characterization criteria to optimize an APSP algorithm implementation for NVIDIA GPUs. Our experimental results show that the combined use of proper configuration policies, and the concurrent kernels capability of new CUDA architectures, leads to a performance improvement of up to 62 % with respect to one of the possible configurations recommended by CUDA, considered as baseline.This research has been partially supported by Ministerio de Economía y Competitividad (Spain) and ERDF program of the European Union: CAPAP-H4 network (TIN2011-15734-E), MOGECOPP project (TIN2011-25639); and Junta de Castilla y León (Spain) ATLAS project (VA172A12-2)

Du mythe du « retard » au mythe de la « modernisation » ou l'adaptation des agricultures du sud de l'Europe à la Politique agricole commune : le cas de l'Estrémadure espagnole

Ce travail se veut une réflexion sur le changement social en agriculture, changement qui a commencé dès la fin des années 1980, lorsque le modèle dominant de l'agriculture européenne semblait ne plus tenir le cap et que le monde se déclarait en crise. Pendant cette période, les fondements productifs de la PAC sont remis en cause et, au sein de la CEE, en particulier en France, un même discours fait écho : le modèle dominant surnommé « modèle productiviste » ne pouvait, à lui seul, déso..