Peer-reviewed Publications |
Barreau, L., Veyrinas, K., Gruson, V., Weber, S. J., Auguste T, Hergott, J. - F., Lepetit F, Carre B, Houver J.-C., Dowek, D., & Salieres, P. (2018). Evidence of depolarization and ellipticity of high harmonics driven by ultrashort bichromatic circularly polarized fields. Nat Commun, 9, 4727.
Résumé: High harmonics generated by counter-rotating laser fields at the fundamental and second harmonic frequencies have raised important interest as a table-top source of circularly polarized ultrashort extreme-ultraviolet light. However, this emission has not yet been fully characterized: in particular it was assumed to be fully polarized, leading to an uncertainty on the effective harmonic ellipticity. Here we show, through simulations, that ultrashort driving fields and ultrafast medium ionization lead to a breaking of the dynamical symmetry of the interaction, and consequently to deviations from perfectly circular and fully polarized harmonics, already at the single-atom level. We perform the complete experimental characterization of the polarization state of high harmonics generated along that scheme, giving direct access to the ellipticity absolute value and sign, as well as the degree of polarization of individual harmonic orders. This study allows defining optimal generation conditions of fully circularly polarized harmonics for advanced studies of ultrafast dichroisms.
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Becker D., Lachmann M. D., Seidel S. T., Ahlers H., Amri S., Charron E., Corgier R., Franz T., Gaaloul N., Grosse J., Hellmig O., Herr W., Lüdtke D., Müntinga H., Popp M., Schkolnik V., Wendrich T., Wenzlawski A., Weps B., Braxmeier C., Ertmer W., Krutzik M., Lämmerzahl C., Peters A., Schleich W. P., Sengstock K., Walser R., Windpassinger P., & Rasel E. M. (2018). Space-borne Bose-Einstein condensation for precision interferometry. Nature, 562, 391.
Résumé: Owing to the low-gravity conditions in space, space-borne laboratories enable experiments with extended free-fall times. Because Bose–Einstein condensates have an extremely low expansion energy, space-borne atom interferometers based on Bose–Einstein condensation have the potential to have much greater sensitivity to inertial forces than do similar ground-based interferometers. On 23 January 2017, as part of the sounding-rocket mission MAIUS-1, we created Bose–Einstein condensates in space and conducted 110 experiments central to matter-wave interferometry, including laser cooling and trapping of atoms in the presence of the large accelerations experienced during launch. Here we report on experiments conducted during the six minutes of in-space flight in which we studied the phase transition from a thermal ensemble to a Bose–Einstein condensate and the collective dynamics of the resulting condensate. Our results provide insights into conducting cold-atom experiments in space, such as precision interferometry, and pave the way to miniaturizing cold-atom and photon-based quantum information concepts for satellite-based implementation. In addition, space-borne Bose–Einstein condensation opens up the possibility of quantum gas experiments in low-gravity conditions.
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Blancard C., Cubaynes D., Guilbaud S., & and Bizau J.-M. (2018). Absolute Photoionization Cross Section for Fe6+ to Fe10+ Ions in the Photon Energy Region of the 2p–3d Resonance Lines. The Astrophysical Journal, 853(1), 32.
Résumé: Resonant single photoionization cross sections of Fen+ (n = 6 to 10) ions have been measured in absolute values using a merged-beams setup at the SOLEIL synchrotron radiation facility. Photon energies were between about 710 and 780 eV, covering the range of the 2p–3d transitions. The experimental cross sections are compared to calculations we performed using a multi-configuration Dirac–Fock code and the OPAS code dedicated to radiative opacity calculations. Comparisons are also done with the Chandra X-ray observatory NGC 3783 spectra and with the results of previously published calculations.
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Chin, A., Mangaud, E., Atabek, O., & Desouter-Lecomte, M. (2018). Coherent quantum dynamics launched by incoherent relaxation in a quantum circuit simulator of a light-harvesting complex. Phys. Rev. A, 97(6), 063823.
Résumé: Engineering and harnessing coherent excitonic transport in organic nanostructures has recently been suggested as a promising way towards improving manmade light-harvesting materials. However, realizing and testing the dissipative system-environment models underlying these proposals is presently very challenging in supramolecular materials. A promising alternative is to use simpler and highly tunable “quantum simulators” built from programmable qubits, as recently achieved in a superconducting circuit by Potočnik et al. [A. Potočnik et al., Nat. Commun. 9, 904 (2018)]. We simulate the real-time dynamics of an exciton coupled to a quantum bath as it moves through a network based on the quantum circuit of Potočnik et al. Using the numerically exact hierarchical equations of motion to capture the open quantum system dynamics, we find that an ultrafast but completely incoherent relaxation from a high-lying “bright” exciton into a doublet of closely spaced “dark” excitons can spontaneously generate electronic coherences and oscillatory real-space motion across the network (quantum beats). Importantly, we show that this behavior also survives when the environmental noise is classically stochastic (effectively high temperature), as in present experiments. These predictions highlight the possibilities of designing matched electronic and spectral noise structures for robust coherence generation that do not require coherent excitation or cold environments.
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Corgier R., Amri S., Herr W., Ahlers H., Guéry-Odelin D., Rasel E. M., Charron E., & Gaaloul N. (2018). Fast manipulation of Bose-Einstein condensates with an atom chip. New J. Phys., 20(5), 055002.
Résumé: We present a detailed theoretical analysis of the implementation of shortcut-to-adiabaticity protocols for the fast transport of neutral atoms with atom chips. The objective is to engineer transport ramps with durations not exceeding a few hundred milliseconds to provide metrologically relevant input states for an atomic sensor. Aided by numerical simulations of the classical and quantum dynamics, we study the behavior of a Bose-Einstein condensate in an atom chip setup with realistic anharmonic trapping. We detail the implementation of fast and controlled transports over large distances of several millimeters, i.e. distances 1000 times larger than the size of the atomic cloud. A subsequent optimized release and collimation step demonstrates the capability of our transport method to generate ensembles of quantum gases with expansion speeds in the picokelvin regime. The performance of this procedure is analyzed in terms of collective excitations reflected in residual center of mass and size oscillations of the condensate. We further evaluate the robustness of the protocol against experimental imperfections.
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Devolder, A., Luc-Koenig, E., Atabek, O., Desouter-Lecomte, M., & Dulieu, O. (2018). Proposal for the formation of ultracold deeply bound RbSr dipolar molecules by all-optical methods. Phys. Rev. A, 98(5), 053411.
Résumé: Ultracold paramagnetic and polar diatomic molecules are among the promising systems for quantum simulation of lattice-spin models. Unfortunately, their experimental observation is still challenging. Based on our recent ab initio calculations, we analyze the feasibility of all-optical schemes for the formation of ultracold 87Rb84Sr bosonic molecules. A first possibility is photoassociation followed by spontaneous emission. The photoassociation rate coefficients toward electronic states converging to the 87Rb(5s2S1/2)+84Sr(5s5p3P0,1,2) asymptotes are particularly small for vibrational levels close to the asymptote. The creation of molecules would be more interesting by using deeply bound levels which preferentially relax to the v''=0 level of the ground state. On the other hand, the photoassociation rate coefficients toward electronic states correlated to the Rb(5p2P1/2,3/2)+Sr(5s21S0) are significant for levels close to the asymptote. The spontaneous emission thus creates weakly bound molecules in a single vibrational level. A second option relies on stimulated Raman adiabatic passage implemented in a tight optical trap. It efficiently creates weakly bound ground-state molecules in a well-defined level, thus providing a promising alternative to magnetic Feshbach resonances for further population transfer toward the absolute ground state of the RbSr molecule.
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Gatti, F. (2018). Molecular dynamics simulated by photons. Nature, 557, 641.
Résumé: The microscopic behaviour of molecules can be difficult to model using ordinary computers because it is governed by quantum physics. A photonic chip provides a versatile platform for simulating such behaviour.
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Holzmeier, F., Bello, R. Y., Herve, M., Achner, A., Baumann, T. M., Meyer, M., Finetti, P., Di Fraia, M., Gauthier, D., Roussel, E., Plekan, O., Richter, R., Prince, K. C., Callegari, C., Bachau, H., Palacios, A., Martin, F., & Dowek, D. (2018). Control of H2 Dissociative Ionization in the Nonlinear Regime Using Vacuum Ultraviolet Free-Electron Laser Pulses. Phys Rev Lett, 121(10), 103002.
Résumé: The role of the nuclear degrees of freedom in nonlinear two-photon single ionization of H_{2} molecules interacting with short and intense vacuum ultraviolet pulses is investigated, both experimentally and theoretically, by selecting single resonant vibronic intermediate neutral states. This high selectivity relies on the narrow bandwidth and tunability of the pulses generated at the FERMI free-electron laser. A sustained enhancement of dissociative ionization, which even exceeds nondissociative ionization, is observed and controlled as one selects progressively higher vibronic states. With the help of ab initio calculations for increasing pulse durations, the photoelectron and ion energy spectra obtained with velocity map imaging allow us to identify new photoionization pathways. With pulses of the order of 100 fs, the experiment probes a timescale that lies between that of ultrafast dynamical processes and that of steady state excitations.
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Kennedy, E. T., Mosnier, J. - P., van Kampen, P., Bizau, J. - M., Cubaynes, D., Guilbaud, S., Carniato, S., Puglisi, A., & Sisourat, N. (2018). Evolution of L-shell photoabsorption of the molecular-ion series SiH_n^+(n=1,2,3): Experimental and theoretical studies. Phys. Rev. A, 97(4), 043410.
Résumé: We report on complementary laboratory and theoretical investigations of the 2p photoexcitation cross sections for the molecular-ion series SiHn+ (n=1,2,3) near the L-shell threshold. The experiments used an electron cyclotron resonance (ECR) plasma molecular-ion source coupled with monochromatized synchrotron radiation in a merged-beam configuration. For all three molecular ions, the Si2+ decay channel appeared dominant, suggesting similar electronic and nuclear relaxation patterns involving resonant Auger and dissociation processes, respectively. The total yields of the Si2+ products were recorded and put on absolute cross-section scales by comparison with the spectrum of the Si+ parent atomic ion. Interpretation of the experimental spectra ensued from a comparison with total photoabsorption cross-sectional profiles calculated using ab initio configuration interaction theoretical methods inclusive of vibrational dynamics and contributions from inner-shell excitations in both ground and valence-excited electronic states. The spectra, while broadly similar for all three molecular ions, moved towards lower energies as the number of screening hydrogen atoms increased from one to three. They featured a wide and shallow region below ∼107eV due to 2p→σ∗ transitions to dissociative states, and intense and broadened peaks in the ∼107–113−eV region merging into sharp Rydberg series due to 2p→nδ,nπ transitions converging on the LII,III limits above ∼113eV. This overall spectral shape is broadly replicated by theory in each case, but the level of agreement does not extend to individual resonance structures. In addition to the fundamental interest, the work should also prove useful for the understanding and modeling of astronomical and laboratory plasma sources where silicon hydride molecular species play significant roles.
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Mangaud E., P. - J. R., Sugny D., Meier C., Atabek O, & Desouter-Lecomte M. (2018). Non-Markovianity in the optimal control of an open quantum system described by hierarchical equations of motion. New J. Phys., 20, 043050.
Résumé: Optimal control theory is implemented with fully converged hierarchical equations of motion (HEOM) describing the time evolution of an open system density matrix strongly coupled to the bath in a spin-boson model. The populations of the two-level sub-system are taken as control objectives; namely, their revivals or exchange when switching off the field. We, in parallel, analyze how the optimal electric field consequently modifies the information back flow from the environment through different non-Markovian witnesses. Although the control field has a dipole interaction with the central sub-system only, its indirect influence on the bath collective mode dynamics is probed through HEOM auxiliary matrices, revealing a strong correlation between control and dissipation during a non-Markovian process. A heterojunction is taken as an illustrative example for modeling in a realistic way the two-level sub-system parameters and its spectral density function leading to a non-perturbative strong coupling regime with the bath. Although, due to strong system-bath couplings, control performances remain rather modest, the most important result is a noticeable increase of the non-Markovian bath response induced by the optimally driven processes.
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Mendive-Tapia, D., Mangaud, E., Firmino, T., de la Lande, A., Desouter-Lecomte, M., Meyer, H. D., & Gatti, F. (2018). Multidimensional Quantum Mechanical Modeling of Electron Transfer and Electronic Coherence in Plant Cryptochromes: The Role of Initial Bath Conditions. Journal Of Physical Chemistry B, 122(1), 126–136.
Résumé: A multidimensional quantum mechanical protocol is used to describe the photoinduced electron transfer and electronic coherence in plant cryptochromes without any semiempirical, e.g., experimentally obtained, parameters. Starting from a two-level spin-boson Hamiltonian we look at the effect that the initial photoinduced nuclear bath distribution has on an intermediate step of this biological electron transfer cascade for two idealized cases. The first assumes a slow equilibration of the nuclear bath with respect to the previous electron transfer step that leads to an ultrafast decay with little temperature dependence; while the second assumes a prior fast bath equilibration on the donor potential energy surface leading to a much slower decay, which contrarily displays a high temperature dependence and a better agreement with previous theoretical and experimental results. Beyond Marcus and semiclassical pictures these results unravel the strong impact that the presence or not of equilibrium initial conditions has on the electronic population and coherence dynamics at the quantum dynamics level in this and conceivably in other biological electron transfer cascades.
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Puglisi A., M. T., Kennedy E.T., Mosnier J.P., Bizau J.M., Cubaynes D., Sisourat N. and Carniato S. (2018). X-ray photochemistry of carbon hydride molecular ions. Physical Chemistry Chemical Physics, 20, 4415.
Résumé: Hydride molecular ions are key ingredients of the interstellar chemistry since they are precursors of more complex molecules. In regions located near a soft X-ray source these ions may resonantly absorb an X-ray photon which triggers a complex chain of reactions. In this work, we simulate ab initio the X-ray absorption spectrum, Auger decay processes and the subsequent fragmentation dynamics of two hydride molecular ions, namely CH2+ and CH3+. We show that these ions feature strong X-ray absorption resonances which relax through Auger decay within 7 fs. The doubly-charged ions thus formed mostly dissociate into smaller ionic carbon fragments: in the case of CH2+, the dominant products are either C+/H+/H or CH+/H+. For CH3+, the system breaks primary into CH2+ and H+, which provides a new route to form CH2+ near a X-ray source. Furthermore, our simulations provide the branching ratios of the final products formed after the X-ray absorption as well as their kinetic and internal energy distributions. Such data can be used in the chemistry models of the interstellar medium.
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Puthumpally-Joseph R., Mangaud E., Chevet V., Desouter-Lecomte M., Sugny D., & Atabek O. (2018). Basic mechanisms in the laser control of non-Markovian dynamics. Phys. Rev. A, 97(3), 033411.
Résumé: Referring to a Fano-type model qualitative analogy we develop a comprehensive basic mechanism for the laser control of the non-Markovian bath response and fully implement it in a realistic control scheme, in strongly coupled open quantum systems. Converged hierarchical equations of motion are worked out to numerically solve the master equation of a spin-boson Hamiltonian to reach the reduced electronic density matrix of a heterojunction in the presence of strong terahertz laser pulses. Robust and efficient control is achieved increasing by a factor of 2 the non-Markovianity measured by the time evolution of the volume of accessible states. The consequences of such fields on the central system populations and coherence are examined, putting the emphasis on the relation between the increase of non-Markovianity and the slowing down of decoherence processes.
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Zanuttini, D., Gatti, F., & Marquardt, R. (2018). CO quantum dynamics diffusion on Cu(1 0 0). Chemical Physics, 509, 3–12.
Résumé: We present a quantum mechanical study of the diffusion of CO molecules on the Cu(0 0 1) surface. We use the Strasbourg-Amsterdam-Postdam potential surface and a “non-tunnel”-variant hereof; to mimic an initial state that is localized in one adsorption well, a “local-potential-shift” concept is introduced; the Multi Configuration Time Dependent Hartree method to perform the calculations. Special emphasis is placed on the effect of the dimensionality of the models. Surprisingly, tunneling plays an important role typically 1 ps after the beginning of the dynamics; it dominates at around 1 ns and might, at least partly, explain the long diffusion rates measured experimentally for the system.
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Zhao, Z. Q., Chen, J., Zhang, Z. J., Zhang, D. H., Wang, X. G., Carrington, T., & Gatti, F. (2018). Computing energy levels of CH4, CHD3, CH3D, and CH3F with a direct product basis and coordinates based on the methyl subsystem. JOURNAL OF CHEMICAL PHYSICS, 148(7), 074113.
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