Transporte de electrones de baja energía en gases moleculares

Ana Lozano (IFF, CSIC)
Date & location:   Thu 13 Dic  2018 12:30:00 GMT+0200 (CEST), Meeting Room, Serrano 121 (CFMAC)

En este estudio se presentan medidas experimentales novedosas de secciones eficaces totales de colisión de electrones de baja energía (1-300 eV) con moléculas de interés biológico en fase gaseosa: para-benzoquinona, piridina, sevofluorano y tiofeno. Para la realización de dichas medidas, se ha optimizado y validado un dispositivo experimental estado del arte basado en el transporte de electrones en condiciones de confinamiento magnético. La incertidumbre experimental asociada a todo el conjunto de datos presentados es inferior al 5%. Además, se ha proporcionado una estimación adecuada de un error sistemático inherente al aparato de medida derivado del confinamiento magnético del haz. En estas condiciones se han podido identificar resonancias asignadas a la formación temporal de iones negativos, tanto en casos en los que elelectrón incidente se ve atrapado por la forma del potencial molecular (“shape resonances”) como aquellos en los que la captura viene acompañada de la excitación de un nivel electrónico (“core excited resonances”)

La validación del conjunto de datos experimentales que conforman este estudio se ha realizado: Primero, a través de un análisis crítico de los resultados obtenidos y la comparación con otros resultados disponibles en la literatura, así como con los datos obtenidos a partir de los formalismos teóricos IAM-SCAR y R-matrix para el presente estudio y segundo, mediante la simulación por Monte Carlo del transporte de electrones en los gases estudiados, utilizando los presentes resultados como datos de entrada, y su comparación con los espectros de transmisión experimentales.

Daño por radiación a nivel molecular en aplicaciones biomédicas

Rafael Colmenares (IFF, CSIC)
Date & location:   Thu 22 Nov  2018 12:30:00 GMT+0200 (CEST), Meeting Room, Serrano 121 (CFMAC)

El papel de los electrones de energías bajas en el daño molecular en términos de roturas o disociaciones, independientemente del tipo de haz primario, es un campo de actualidad científica. Por un lado, los modelos teóricos de colisiones de electrones en medios condensados para energías menores de 100 eV presentan diferencias metodológicas y discrepancias importantes en los resultados. Por otro, a pesar de que el daño en el ADN se produce a escala molecular, no existe una teoría que permita relacionar la información a esta escala con el daño biológico observado o medido. De hecho, la dosis absorbida, pese a ser una magnitud macroscópica que pierde los detalles de la escala en la que se produce realmente el daño, es la magnitud de referencia en los tratamientos con radiaciones ionizantes.

Los códigos Monte Carlo de evento por evento, en los que la energía de corte en la simulación del transporte de electrones se sitúa en niveles de pocos eV o incluso menos, son una potente herramienta para estudiar las interacciones a escala molecular. LEPTS (Low Energy Particle Track Simulation code) es un programa de este tipo, que contiene información física (secciones eficaces de colisión y espectros de pérdida de energía) para moléculas de interés biológico. En las simulaciones de LEPTS se incluyen todas las vías de colisión electrón-molécula que han demostrado tener capacidad de dañar al ADN. Algunas de estas colisiones, que solo se producen en energía bajas y transfieren poca energía, pueden ser, sin embargo, muy eficientes en términos de daño molecular.

En este trabajo, en una primera parte, se describen las medidas experimentales realizadas para la obtención de esta información física en algunas biomoléculas para su incorporación en LEPTS.

En una segunda parte, el papel en situaciones clínicas de las interacciones poco energéticas (pero con capacidad de generar daño) es estudiado en comparación con la dosis absorbida, a través de LEPTS, los sistemas de cálculo clínicos y datos experimentales.

Particle-Molecule Interactions for Radiation and Plasma Treatment Models

Lilian Ellis-Gibbings (IFF, CSIC)
Date & location:   Fri 21 Sep  2018 12:00:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

The details of low energy collision processes are necessary for modelling both the effect of plasma treatment and the electron cascade produced in radiotherapy. This summary of the doctoral thesis by the same name includes both experimental and calculated cross section databases, electron energy loss spectra, fragmentation via DEA and electron transfer, and the effects of condensation of the target.

Estudio computacional de solvatación de cationes de átomos alcalinos con helio e hidrógeno

Josu Ortiz de Zárate (IFF, CSIC)
Date & location:   Fri 14 Sep  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Las nanagotas de helio ofrecen una buena oportunidad para estudiar la solvatación de cationes de átomos alcalinos. En esta charla se pretende mostrar un estudio computacional de clústeres de (He)nLi+ [1] y (H2)nCs+ junto con medidas experimentales obtenidas de espectros de masas realizadas por Scheier y colaboradores [1,2]. Para estimar las interacciones se utiliza un potencial de Pirani [3] con parámetros optimizados a partir de cálculos ab initio. La estructura y estabilidad de los clústeres se analiza mediante distintos métodos, clásicos y cuánticos, como son: Basin Hopping, Monte Carlo Clásico, Diffusion Monte Carlo y Path Integral Monte Carlo. También se detallará el papel de los efectos de inducción de tres cuerpos en (He)nLi+ y de los grados de libertad rotacionales del H2 en (H2)nCs+.

Referencias:
[1]  Rastogi, M.; Leidlmair, C.; An der Lan, L.; Ortiz de Zárate, J.; Pérez de Tudela, R.; M. Bartolomei, M.; Hernández, M. I.; Campos-Martínez, J.; González-Lezana, T.; Hernández-Rojas, J.; Bretón, J.; Scheier, P.; Gatchell, M. Phys. Chem. Chem. Phys., 2018, 10.1039/C8CP04522D.
[2]  Kranabetter L.; Goulart, M.; Aleem, A.; Kurzhaler, T.; Kuhn, M.; Barwa, E.; Renzler, M.; Grubwieser, L.; Schwärzler, M.; Kaiser, A.; Scheier, P. J. Phys. Chem. C, 2017, 121, 10887.
[3]  Pirani, F.; Brizi, S.; Roncaratti, L.; Casavecchia, P.; Cappelletti, D.; Vecchicattivi, F. Phys. Chem. Chem. Phys., 2008, 10, 5489.

Quantum dynamics studies on bimolecular reactions of practical and fundamental interest

Rajagopala Rao(Indian Institute of Technology Patna)
Date & location:   Thu 12 Jul  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Obtaining the ro-vibrational state resolved reaction attributes is a formidable challenge both for the theoreticians and experimentalists. Atom + diatom reactions have been used as a prototype to study some important quantum effects like geometric phase (example: H + H2reaction) [1], non-adiabatic coupling effects (Cl + H2 reaction) [2] and nuclear spin symmetry effects (O + O2 reaction). The latter exists in the molecules with all identical nuclei. In the case of O3 or H3+, all the three nuclei are identical and hence indistinguishable under cyclic permutation ( thus belongs to P3 permutation symmetry group). The total wavefunction (including nuclear spin) is required to be either symmetric (for bosons) or antisymmetric (for fermions) with respect to interchange of the identical nuclei. Hence a full quantum mechanical calculations should take these spin statistics into consideration. In one of my recent works [3] on the O + O2 and H+ + H2 collision dynamics, we found that the inclusion of proper spin statistics is essential for obtaining the desirable results.

References:

[1] J. Jankunas, M. Sneha, R. N. Zare, F. Bouakline, and S. C. Althorpe J. Chem. Phys. 139, 144316 (2013).
[2] E. Garand, J. Zhou, D.E. Manolopoulos, M.H. Alexander, D.M. Neumark, Science 319, 72 (2008).
[3] T. Rajagopala Rao, G. Guillon, S. Mahaatra, P. Honvault J. Phys. Chem. Lett. 6,633 (2015).

Long-lasting coherence in biological complexes: from microscopic models to actual experiments

Javier Prior (Universidad Politécnica de Cartagena)
Date & location:   Fri 15 Jun  2018 12:00:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Recent observations of oscillatory features in the optical response of photosynthetic complexes have revealed evidence for surprisingly long-lasting electronic coherences which can coexist with energy transport. This observation has generated different questions like: Is  quantum coherence responsible for the surprisingly high efficiency of  natural light harvesters? If so, how do such systems avoid the loss of coherence due to interactions with their warm, wet and noisy environments? The answer to these important questions rests in the beneficial interplay between electronic and vibrational degrees of freedom.

FOUCAULT PENDULUM, GIRATOR-COUPLED RESONANT CIRCUITS AND NEUTRAL KAONS: A GEOMETRICAL VIEWPOINT

Carlos García Canal (Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina)
Date & location:   Wed 13 Jun  2018 12:00:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

A careful visit to the systems mentioned in the title allows one to find an equivalence among their dynamics. From this finding, a geometrical interpretation of the complex phase of he Cabibbo-Kobayashi-Maskawa matrix naturally appears.

Molecules in space

Marcelino Agúndez (IFF, CSIC)
Date & location:   Wed 06 Jun  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

The interstellar medium is a harsh environment exposed to energetic radiation, where the survival of molecules does not seem favorable. However, molecules are found in many different types of interstellar and circumstellar clouds. The study of molecules has a twofold interest. On the one hand, they serve as excellent tools to characterize the physical conditions prevailing in the clouds. In some clouds that are heavily obscured at optical wavelengths, observing molecules is the only way to get access to the temperature, density, and kinematics of the internal regions. On the other hand, knowing how molecules are synthesized and why different environments host different types of molecules allows to understand the chemical evolution that matter experiences along the process in which stars and planets form. For this latter purpose, chemical models are an essential tool, and these models need to be fed by molecular data coming from laboratory experiments and theoretical calculations. A strong relation between astronomers and physicist and chemists is thus a must to correctly understand the physical and chemical evolution of matter along the life cycle of stars.

References:

Agúndez, M., & Wakelam, V. 2013, Chemical Reviews, 113, 8710. http://adsabs.harvard.edu/abs/2013ChRv..113.8710A
Herbst, E. The chemistry of interstellar space. Chem. Soc. Rev., 2001, 30, 168-176.  http://pubs.rsc.org/en/content/articlelanding/2001/cs/a909040a#!divAbstract

Airborne Infrared Astronomy with SOFIA

Hans Zinneker (Deutsches SOFIA Institut)
Date & location:   Thu 24 May  2018 12:00:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an 80/20 joint project of NASA and the German Aerospace Center (DLR) to operate an airborne observatory. SOFIA is based on a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aircraft fuselage that can be opened in flight to allow a 2.5 m diameter reflecting telescope access to the sky. This telescope is designed for infrared astronomy observations in the stratosphere at altitudes of about 12 kilometers. The primary science objectives of SOFIA are to study the composition of planetary atmospheres and surfaces; to investigate the structure, evolution and composition of comets; to determine the physics and chemistry of the interstellar medium; and to explore the formation of stars and other stellar objects. In this talk, we will review the capabilities of SOFIA, with an emphasis on molecular spectroscopy and astrochemistry studies.

The role of computational modelling in catalysis and gas adsorption/separation with metal organic frameworks 

Andreas Mavrandonakis (IMDEA Energy)
Date & location:   Wed 23 May  2018 12:30:00 GMT+0200 (CEST), Meeting Room, Serrano 113-bis (CFMAC)

First-principles quantum Porous coordination materials such as metal/covalent organic frameworks (MOFs/COFs) have attracted considerable interest for their potential use in catalysis and gas adsorption and/or separation. In this work, several computational chemistry tools are used to explain the structure and reactivity of Metal Organic Frameworks for applications in catalysis and gas adsorption/separation. The complex dehydration process of NU-1000 will be presented. NU-1000 is a MOF that has a unique mixed proton topology, with significant importance in catalysis, acid/base chemistry and deposition of metal atoms on the nodes of the framework. Based on experimental results, it is suggested that the Zr6Ox nodes undergo structural distortions upon heating [1]. We try to assign the structural distortions in NU-1000 and compare with the phase transitions in bulk zirconia. Moreover, the importance of open metal sites will be emphasized, with focus on the energetics and vibrational properties of various adsorbed gaseous molecules [2, 3, 4, 5].

[1] Platero-Prats, A. E.; Mavrandonakis, A.; Gallington, L. C.; Liu, Y.; Hupp, J. T.; Farha, O. K.; Cramer, C. J.; Chapman, K. W. J. Am. Chem. Soc. 2016, 138, 4178–4185.
[2] Wang, Z.; Sezen, H.; Liu, J.; Yang, C.; Roggenbuck, S. E.; Peikert, K.; Froba, M.; Mavrandonakis, A.; Supronowicz, B.; Heine, T.; Gliemann, H.; Woll, C. Microporous Mesoporous Mater. 2015, 207, 53–60.
[3] Oh, H.; Savchenko, I.; Mavrandonakis, A.; Heine, T.; Hirscher, M. ACS Nano 2014, 8, 761–770.
[4] Weinrauch, I.; Savchenko, I.; Denysenko, D.; Souliou, S. M.; Kim, H.-H.; Le Tacon, M.; Daemen, L. L.; Cheng, Y.; Mavrandonakis, A.; Ramirez-Cuesta, A. J.; Volkmer, D.; Schutz, G.; Hirscher, M.; Heine, T. Nat. Commun. 2017, 8, 14496.
[5] Mavrandonakis, A.; Vogiatzis, K. D.; Boese, A. D.; Fink, K.; Heine, T.; Klopper, W. Inorg. Chem. 2015, 54, 8251–8263.

Non-Equilibrium Quantum Dynamics and Conservation Laws: A Trapped-Ion Experiment Proposal.

Jordi Mur-Petit (Clarendon Laboratory, Oxford University)
Date & location:   Fri 11 May  2018 14:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Non-equilibrium dynamics of quantum many-body systems pose some of the most challenging open problems in Physics, such as how do quantum systems relax towards equilibrium or how could it be possible to extract work from them [1]. The emergent field of quantum thermodynamics applies principles and ideas from statistical mechanics and provides general results about these open questions. Among these results, the quantum fluctuation relations (QFRs) are especially powerful, as they lead to the formulation of new measurement protocols for thermometry in ultra-cold setups [2] and on work statistics in out-of-equilibrium processes [3], as recently demonstrated in pioneering experiments with trapped ions [4].

I will offer a review of these advances and discuss the limitations of QFRs when trying to obtain information about a quantum system with conserved charges. After this, I will present a new set of generalized fluctuation relations that are suitable for such a system, and illustrate its impact in a proposed trapped-ion experiment [5].

I will also provide an overview of ongoing research at interrogating complex quantum systems with quantum probes [6], and talk about new avenues opened up by certain recent advances that have been made concerning the trapping and cooling of diatomic molecules [7].

[1] See S. Vinjanampathy, J. Anders, Contemp. Phys. 57, 545 (2016) for a recent review.
[2] T. H. Johnson et al., Phys. Rev. A 93, 053619 (2016).
[3] R. Dorner et al., Phys. Rev. Lett. 110, 230601 (2013); also L. Mazzola et al., ibid. 110, 230602 (2013), and T. B. Batalhão et al., ibid. 113, 140601 (2014).
[4] S. An et al., Nature Phys. 11, 193 (2015); also J. Roßnagel et al., Science 352, 325 (2016).
[5] J. Mur-Petit, A. Relaño, R. A. Molina, D. Jaksch, Nature Comms. (2018); in the press, preprint available at arXiv:1711.00871.
[6] A. Usui, B. Buča, J. Mur-Petit. Quantum probe spectroscopy for cold atomic systems [arXiv:1804.09237].
[7] J. A. Blackmore et al., Ultracold Molecules: A Platform for Quantum Simulation [arXiv:1804.02372].

Benchmarking chemical reactivity in the deep tunnelling regime: the ultra-col behaviours of the F+H2

Dario de Fazio (Instituto de Struttura della Materia, CNR)
Date & location:   Wed 18 Apr  2018 12:30:00 GMT+0200 (CEST), Meeting Room, Serrano 113-bis (CFMAC)

Recent attention to cold environments, either in the laboratory or under astrophysical and other conditions, is putting at the forefront the tunnel effect, a principal source of deviations from the Arrhenius rate law. Progress in theoretical chemical kinetics relies on accurate knowledge of potential energy surfaces, as provided by advanced quantum chemistry and tested against experiments [1]. To generate accurate rate data, quantum scattering calculations involve sophisticated algorithms to produce scattering matrix elements at given angular momenta (to be summed to yield cross sections) and as a function of collision velocities (to be integrated to give rate constants and temperature dependencies). Here illustrated are these passages, a milestone having been benchmark temperature dependent rate constants for the prototypical F + H2 reaction [2], recently validated by experiments in the moderate tunnelling regime [3]. The F+ HD variant permits exploring tunnel as well as isotopic effects [4] and developing a phenomenology and interpretive ingredients down to the deep tunnelling regime [5,6] where the reactivity is strongly dominated by resonances and quantum effects. In the seminar we will discuss and compare cold and ultra-cold reactive behaviours of the F+H2 reaction and of its isotopic variants (F+HD and F+D2) to deeply understand its dependence by the entrance channel behaviour of the potential energy surface [2]. Simplified dynamical treatments and ultra-cold theories will be employed to understand the various resonance features obtained by ‘exact’ quantum reactive scattering results and as they affect cross sections and kinetic behaviours.

[1] D. De Fazio, S. Cavalli and V. Aquilanti; J. Phys. Chem. A, 120 (2016) 5288.
[2] V. Aquilanti, S. Cavalli, D. De Fazio, A. Volpi, A. Aguilar, J. M. Lucas; Chem. Phys. 308, 237 (2005).
[3] M. Tizniti, S. D. Le Picard, F. Lique, C. Berteloite, A. Canosa, M. H. Alexander, I. R. Sims; Nat. Chem., 6, 141 (2014).
[4] D. De Fazio, V. Aquilanti, S. Cavalli, A. Aguilar, J. M. Lucas; J.Chem. Phys. 125, 133109 (2006).
[5] V. Aquilanti, K.C. Mundim, S. Cavalli, D. De Fazio, A. Aguilar, J. M. Lucas; Chem. Phys., 398,186-191 (2012). [6] S. Cavalli, V. Aquilanti, K. C. Mundim, D De Fazio; J Phys Chem A, 118, 6632–6641 (2014).

Agregados de esferas magnéticas: Mapas energéticos y transiciones estructurales

Javier Hernández Rojas (Universidad de La Laguna)
Date & location:   Wed 21 Mar  2018 12:30:00 GMT+0200 (CEST), Meeting Room, Serrano 113-bis (CFMAC)

El autoensamblaje es un proceso espontáneo de formación de estructuras ordenadas a partir de constituyentes más o menos desordenados. En particular, la creación de superestructuras magnéticas formadas por esferas con momentos dipolares magnéticos permanentes (magnetos), es de gran interés por las muchas aplicaciones que tienen estos sistemas en diferentes áreas científicas y/o tecnológicas. En este seminario presentaremos un modelo de interacción entre magnetos [1], basado en interacciones de corto y largo alcance. Para las fuerzas de corto alcance utilizaremos el potencial binario de Morse, mientras que para las de largo alcance emplearemos la interacción estándar entre dipolos magnéticos permanentes. Con este modelo determinaremos las estructuras de mínimo global (las más estables) de hasta 50 agregados de esferas magnéticas. Presentaremos las morfologías más relevantes que se encuentran y que varían desde cadenas lineales, anillos circulares, apilamientos de dos y tres anillos circulares, hasta estructuras compactas basadas en láminas superpuestas. Para algunas estructuras seleccionadas, caracterizaremos su mapa energético [2] y analizaremos algunos caminos de reacción en importantes transiciones estructurales. Finalmente, estudiaremos el efecto de un campo magnético externo sobre estas estructuras.

Referencias:
[1] J. Hernández-Rojas, D. Chakrabarti, D. J. Wales, Phys. Chem. Chem. Phys. 18, 26579 (2016).
[2] D. J. Wales, Energy Landscapes, Cambridge University Press, Cambridge (2003).

Síntesis y propiedades de clústeres de átomos metálicos sin ligandos protectores 

Arturo López Quintela(Universidad de Santiago de Compostela)
Date & location:  Fri 9 Mar  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

En los últimos años se han desarrollado diferentes estrategias de química suave para sintetizar clústeres cuánticos de átomos metálicos (AQCs, atomic quantum clusters), la mayoría de las cuales se basan en el uso de ligandos que enlazan fuertemente (tales como tioles, fosfinas, etc.) con los AQCs, actuando como agentes estabilizantes/protectores para inhibir el crecimiento de los mismos (véase refs. [1]). Sin embargo, la pasivación de los átomos superficiales de los AQCs puede afectar de forma muy notable sus propiedades químico-físicas, tales como catálisis, propiedades biomédicas, etc. En nuestro laboratorio hemos desarrollado la síntesis de AQCs utilizando el control cinético [2] que no precisa el uso de tales ligandos enlazantes (véase refs. [3]) y permite, además, tanto la obtención de muestras de tamaños muy monodispersas como su escalabilidad. Mediante este procedimiento se han sintetizado AQCs desnudos (es decir, sin la presencia de ligandos protectores) y monodispersos de diferentes metales (Au, Ag, Cu,…), con distinto número de átomos (n < ≈ 30), así como estudiado sus propiedades y aplicaciones catalíticas y biomédicas [4]. En la presentación se realizará un breve resumen de los fundamentos de las técnicas de síntesis de AQCs, así como de sus interesantes propiedades (actividades catalíticas, fotocatalíticas y biomédicas), que demuestran que los clústeres metálicos representan una nueva serie de materiales muy estables –térmica y químicamente- y cuyas propiedades difieren completamente de los correspondientes nanomateriales y materiales masivos.

[1] A.C. Templeton et al. Acc.Chem. Res. 33 (2000) 27; P. D. Jadzinsky et al. Science 318 (2007) 430; M. Walter et al. PNAS 105 (2008) 9157; D. Jiang et al. J. Am. Chem. Soc. 130 (2008) 2778.
[2] Y. Piñeiro et al. J. Colloid Interf. Sci. 449 (2015) 279.
[3] A. Ledo-Suárez et al. Angew.Chem, Int. Ed. 46 (2007) 8823; B. Santiago- González et al. Nano Lett. 10 (2010) 4217 ; B. Santiago González et al. Nanoscale 4 (2012) 7632; S. Huseyinova et al. J. Phys. Chem. C 120 (2016) 15902.
[4] N. Vilar- Vidal et al. ACS Catal. 2 (2012) 1693; A. Corma et al. Nat. Chem. 5 (2013) 775; Y. A. Attia et al. J. Am.Chem.Soc. 136 (2014) 1182; D. Buceta et al. Angew. Chem. Int. Ed. 54 (2015) 7612; J. Neissa et al. Chem. Sci. 6 (2015) 6717; M. Cuerva et al. ACS Nano 9 (2015) 10834.

Radiobiological effect of secondary electrons and radicals in radiotherapy 

Gustavo García Gómez-Tejedor (IFF, CSIC)
Date & location:  Wed 28 Feb  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Ionising radiations have been used for decades in radiotherapy treatments of cancer tumours. The radiobiological effectiveness of these radiations is customary assumed to be proportional to the absorbed dose (energy deposited per mass unit). However, Sanche et al. [1] showed that processes involving low energy secondary electrons, whose contribution to the absorbed dose is negligible, are really efficient breaking DNA bases. A similar role can be assumed for the abundant positive, negative and neutral radicals generated during the irradiation which chemically react with key DNA component leading to bond breaking and molecular dissociations. We will review in this seminar the experimental, theoretical and simulation studies we have carried out in the last few years in order to incorporate the effect of secondary electrons and radicals to the current radiotherapy modelling procedures. In addition, a recent proposal to introduce these effects into the radiobiological effectiveness associated to the new hadrontherapy (proton and heavy ion) techniques will be presented [2, 3].

References:
[1] B. Boudaifa, et al. Science 287 1658 (2000).
[2] Radiation Damage in Biomolecualr Systems, G. García and M. Fuss Editors (Springer, London 2012).
[3] M. Durante, et al. Nature Rev. Clin. Oncol. 14 483 (2017).

Quantum information tools to manipulate spacetime: Engineering negative stress-energy densities with quantum energy teleportation

Eduardo Martín Martínez (University of Waterloo, Canada)
Date & location:  Wed 21 Feb  2018 15:00:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

We show how to use quantum energy teleportation in the light-matter interaction as an operational means to create quantum field states that violate energy conditions and have negative local stress-energy densities. We show that the protocol is optimal in the sense that it scales in a way that saturates the quantum interest conjecture and violates energy conditions maximally. We will briefly discuss the backreaction of this protocol on spacetime curvature, and the gravitational properties of the negative energy density created with this process.

Quantum simulation of molecular vibronic spectrum and quantum Rabi model with trapped ion system.

Kiwhan Kim (Tsinghua Unversity, China)
Date & location:  Wed 08 Feb  2018 12:00:00 GMT+0200 (CEST), Meeting Room, Serrano 113-bis (IFF)

In the quite near future, a quantum computer capable of handling 50-100 qubits would be expected to be developed. Such quantum computer is large enough to be impossible to be simulated by existing classical computers, but it may not be sufficient to perform the full quantum error correction and to execute Shor algorithms. Therefore, it is an important question at this stage to find something meaningful tasks with such levels of quantum computers. In this seminar, I’d like to show that an analogue quantum simulation can be a promising solution to perform beyond classical computation by discussing two examples of experimental demonstrations that we’ve recently conducted in our simple system.

The first is the quantum simulation of molecular vibronic spectrum lead by Yangchao Shen [1]. This simulation is a modification of the boson sampling algorithm, which is suitable for showing the power of a quantum computer. Thought the boson sampling algorithm is difficult to perform any useful tasks, by modifying the boson sampling protocol we are able to compute the molecular vibronic spectrum [2]. The trapped ion demonstration employs phonons that can deterministically prepared and detected, which would allow us the sampling of vibronic spectrum beyond photonic systems.

The second is the quantum simulation of quantum Rabi model demonstrated by Dingshun Lv [3]. Currently, the realizations of quantum simulation have been mostly limited to spin models. The quantum Rabi model is the most fundamental model that describes the interaction between spin and field. In particular, when the interaction strength is comparable or larger than the field frequency, various exotic phenomena and ground state entanglement can be occurred, which is observed in our trapped ion quantum simulator.

The current experimental demonstrations are limited to small systems, but we expect that as the system grows, it will provide solutions that exceed the existing limitations without the requirement of full quantum error corrections.

[1] Yangchao Shen, et al., Quantum simulation of molecular spectroscopy in trapped-ion device, Chemical Science DOI: 10.1039/C7SC04602B (2018).
[2] J. Huh, et al., Boson sampling for molecular vibronic spectra, Nature Photon. 9, 615 (2015).
[3] Dingshun Lv, et al., Quantum simulation of the quantum Rabi model in a trapped ion, arXiv:1711.00582 (2017).

Evidences of halogen bonds in clathrate cages

Ramón Hernández-Lamoneda (Centro de Investigaciones Químicas, UAEM México)
Date & location:  Thu 25 Jan  2018 12:30:00 GMT+0200 (CEST), Conference Room, Serrano 121 (CFMAC)

Abstract: Interest in the physicochemical properties of clathrates stems from its potential applications in energy and environment and open questions in basic science. We have been interested in the nature of intermolecular interactions of halogen clathrates as a result of the extensive spectroscopic studies by the groups of Janda and Apkarian. An outstanding result is the significant blue-shift observed in the ultraviolet- visible spectra of different clathrate phases. Large shift values are characteristic of halogen bonding (XB) and can be understood in simple molecular orbital concepts: the electronic transitions involved to the B and C states promote an electron into the sigma antibonding orbital of the dihalogen which is acting as an acceptor of electron density from an oxygen lone pair leading to a repulsive interaction in the excited state. The smaller blue-shifts in the clathrates have been interpreted as showing that no halogen bonding can occur in the cages since all oxygen lone pairs are tied in hydrogen bonding to maintain the cage structure. In this seminar I will present a theoretical characterization of the interaction of Cl2 and Br2 in 512 and 51262 clathrate cages respectively, based on energy partitioning analysis and a study of the electronic shifts associated with transitions to the main valence bands, and I will discuss the characteristics for halogen bonding in the cages.

References:
R. Hernández-Ramoneda, et al. J. Phys. Chem. A 112 (2008) 89-96.
F.A. Batista-Romero, et al. J. Chem. Phys. 143 (2015) 094305; 146 (2017) 144311; 147, (2017) 154301. D. Ochoa-Resendiz, et al. J. Chem. Phys. 145 (2016) 161104.