@article{GorobtsovMercurioBrenneretal.2017,
  author    = {Gorobtsov, O. Yu. and Mercurio, G. and Brenner, G. and Lorenz, Ulf and Gerasimova, N. and Kurta, R. P. and Hieke, F. and Skopintsev, P. and Zaluzhnyy, I. and Lazarev, S. and Dzhigaev, D. and Rose, M. and Singer, A. and Wurth, W. and Vartanyants, I. A.},
  title     = {Statistical properties of a free-electron laser revealed by Hanbury Brown-Twiss interferometry},
  series = {Physical review : A, Atomic, molecular, and optical physics},
  volume    = {95},
  journal   = {Physical review : A, Atomic, molecular, and optical physics},
  number    = {2},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {2469-9926},
  doi       = {10.1103/PhysRevA.95.023843},
  pages     = {16},
  year      = {2017},
  abstract  = {We present a comprehensive experimental analysis of statistical properties of the self-amplified spontaneous emission free-electron laser (FEL) FLASH by means of Hanbury Brown and Twiss interferometry. The experiments were performed at FEL wavelengths of 5.5, 13.4, and 20.8 nm. We determined the second-order intensity correlation function for all wavelengths and different operation conditions of FLASH. In all experiments a high degree of spatial coherence (above 50\%) was obtained. Our analysis performed in spatial and spectral domains provided us with the independent measurements of an average pulse duration of the FEL that were below 60 fs. To explain the complicated behavior of the second-order intensity correlation function we developed an advanced theoretical model that includes the presence of multiple beams and external positional jitter of the FEL pulses. By this analysis we determined that in one of the experiments external positional jitter was about 25\% of the beam size. We envision that methods developed in our study will be used widely for analysis and diagnostics of FEL radiation.},
  language  = {en}
}
@article{SchmidtLorenz2016,
  author    = {Schmidt, Burkhard and Lorenz, Ulf},
  title     = {WavePacket},
  series = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics},
  volume    = {213},
  journal   = {Computer physics communications : an international journal devoted to computational physics and computer programs in physics},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0010-4655},
  doi       = {10.1016/j.cpc.2016.12.007},
  pages     = {223 -- 234},
  year      = {2016},
  abstract  = {WavePacket is an open-source program package for the numerical simulation of quantum-mechanical dynamics. It can be used to solve time-independent or time-dependent linear Schr{\"o}dinger and Liouville-von Neumann-equations in one or more dimensions. Also coupled equations can be treated, which allows to simulate molecular quantum dynamics beyond the Born-Oppenheimer approximation. Optionally accounting for the interaction with external electric fields within the semiclassical dipole approximation, WavePacket can be used to simulate experiments involving tailored light pulses in photo-induced physics or chemistry. The graphical capabilities allow visualization of quantum dynamics 'on the fly', including Wigner phase space representations. Being easy to use and highly versatile, WavePacket is well suited for the teaching of quantum mechanics as well as for research projects in atomic, molecular and optical physics or in physical or theoretical chemistry. The present Part I deals with the description of closed quantum systems in terms of Schr{\"o}dinger equations. The emphasis is on discrete variable representations for spatial discretization as well as various techniques for temporal discretization. The upcoming Part II will focus on open quantum systems and dimension reduction; it also describes the codes for optimal control of quantum dynamics. The present work introduces the MATLAB version of WavePacket 5.2.1 which is hosted at the Sourceforge platform, where extensive Wiki-documentation as well as worked-out demonstration examples can be found.},
  language  = {en}
}
@article{DzhigaevShabalinStankevicetal.2016,
  author    = {Dzhigaev, D. and Shabalin, A. and Stankevic, T. and Lorenz, Ulf and Kurta, R. P. and Seiboth, F. and Wallentin, J. and Singer, A. and Lazarev, S. and Yefanov, O. M. and Borgstrom, M. and Strikhanov, M. N. and Samuelson, L. and Falkenberg, G. and Schroer, C. G. and Mikkelsen, A. and Vartanyants, I. A.},
  title     = {Bragg coherent x-ray diffractive imaging of a single indium phosphide nanowire},
  series = {Journal of optics},
  volume    = {18},
  journal   = {Journal of optics},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {2040-8978},
  doi       = {10.1088/2040-8978/18/6/064007},
  pages     = {10},
  year      = {2016},
  abstract  = {Three-dimensional (3D) Bragg coherent x-ray diffractive imaging (CXDI) with a nanofocused beam was applied to quantitatively map the internal strain field of a single indium phosphide nanowire. The quantitative values of the strain were obtained by pre-characterization of the beam profile with transmission ptychography on a test sample. Our measurements revealed the 3D strain distribution in a region of 150 nm below the catalyst Au particle. We observed a slight gradient of the strain in the range of +/- 0.6\% along the [111] growth direction of the nanowire. We also determined the spatial resolution in our measurements to be about 10 nm in the direction perpendicular to the facets of the nanowire. The CXDI measurements were compared with the finite element method simulations and show a good agreement with our experimental results. The proposed approach can become an effective tool for in operando studies of the nanowires.},
  language  = {en}
}
@article{LorenzSaalfrank2015,
  author    = {Lorenz, Ulf and Saalfrank, Peter},
  title     = {Measures for the non-Markovianity of a harmonic oscillator coupled to a discrete bath derived from numerically exact references},
  series = {The European physical journal : D, Atomic, molecular, optical and plasma physics},
  volume    = {69},
  journal   = {The European physical journal : D, Atomic, molecular, optical and plasma physics},
  number    = {2},
  publisher = {Springer},
  address   = {New York},
  issn      = {1434-6060},
  doi       = {10.1140/epjd/e2014-50727-8},
  pages     = {14},
  year      = {2015},
  abstract  = {System-bath problems in physics and chemistry are often described by Markovian master equations. However, the Markov approximation, i.e., neglect of bath memory effects is not always justified, and different measures of non-Markovianity have been suggested in the literature to judge the validity of this approximation. Here we calculate several computable measures of non-Markovianity for the non-trivial problem of a harmonic oscillator coupled to a large number of bath oscillators. The Multi Configurational Time Dependent Hart ree nietliod is used to provide a numerically converged solution of the system-bath Schrodinger equation, from which the appropriate quantities can be calculated. In particular, we consider measures based on trace-distances and quantum discord for a variety of initial states. These quantities have proven useful in the case of two-level and other small model systems Tpically encountered in quantum optics; but are less straightforward to interpret for the more complex model systems that are relevant for chemical physics.},
  language  = {en}
}
@article{SulyanovaShabalinZozulyaetal.2015,
  author    = {Sulyanova, Elena A. and Shabalin, Anatoly and Zozulya, Alexey V. and Meijer, Janne-Mieke and Dzhigaev, Dmitry and Gorobtsov, Oleg and Kurta, Ruslan P. and Lazarev, Sergey and Lorenz, Ulf and Singer, Andrej and Yefanov, Oleksandr and Zaluzhnyy, Ivan and Besedin, Ilya and Sprung, Michael and Petukhov, Andrei V. and Vartanyants, Ivan A.},
  title     = {Structural Evolution of Colloidal Crystal Films in the Process of Melting Revealed by Bragg Peak Analysis},
  series = {Langmuir},
  volume    = {31},
  journal   = {Langmuir},
  number    = {19},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0743-7463},
  doi       = {10.1021/la504652z},
  pages     = {5274 -- 5283},
  year      = {2015},
  abstract  = {In situ X-ray diffraction studies of structural evolution of colloidal crystal films formed by polystyrene spherical particles upon incremental heating are reported. The Bragg peak parameters, such as peak position, integrated intensity, and radial and azimuthal widths were analyzed as a function of temperature. A quantitative study of colloidal crystal lattice distortions and mosaic spread as a function of temperature was carried out using Williamson-Hall plots based on mosaic block model. The temperature dependence of the diameter of polystyrene particles was obtained from the analysis of Bragg peaks, and the form factor contribution extracted from the diffraction patterns. Four stages of structural evolution in a colloidal crystal upon heating were identified. Based on this analysis, a model of the heating and melting process in the colloidal crystal film is suggested.},
  language  = {en}
}
@article{GorobtsovLorenzKabachniketal.2015,
  author    = {Gorobtsov, Oleg Yu. and Lorenz, Ulf and Kabachnik, Nicolai M. and Vartanyants, Ivan A.},
  title     = {Theoretical study of electronic damage in single-particle imaging experiments at x-ray free-electron lasers for pulse durations from 0.1 to 10 fs},
  series = {Physical review : E, Statistical, nonlinear and soft matter physics},
  volume    = {91},
  journal   = {Physical review : E, Statistical, nonlinear and soft matter physics},
  number    = {6},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1539-3755},
  doi       = {10.1103/PhysRevE.91.062712},
  pages     = {13},
  year      = {2015},
  abstract  = {X-ray free-electron lasers (XFELs) may allow us to employ the single-particle imaging (SPI) method to determine the structure of macromolecules that do not form stable crystals. Ultrashort pulses of 10 fs and less allow us to outrun complete disintegration by Coulomb explosion and minimize radiation damage due to nuclear motion, but electronic damage is still present. The major contribution to the electronic damage comes from the plasma generated in the sample that is strongly dependent on the amount of Auger ionization. Since the Auger process has a characteristic time scale on the order of femtoseconds, one may expect that its contribution will be significantly reduced for attosecond pulses. Here we study the effect of electronic damage on the SPI at pulse durations from 0.1 to 10 fs and in a large range of XFEL fluences to determine optimal conditions for imaging of biological samples. We analyzed the contribution of different electronic excitation processes and found that at fluences higher than 1013-1015 photons/mu m(2) (depending on the photon energy and pulse duration) the diffracted signal saturates and does not increase further. A significant gain in the signal is obtained by reducing the pulse duration from 10 to 1 fs. Pulses below a duration of 1 fs do not give a significant gain in the scattering signal in comparison with 1-fs pulses. We also study the limits imposed on SPI by Compton scattering.},
  language  = {en}
}
@misc{LorenzSaalfrank2015,
  author    = {Lorenz, Ulf and Saalfrank, Peter},
  title     = {Comparing thermal wave function methods for multi-configuration time-dependent Hartree simulations (vol 140, 044106, 2014)},
  series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
  volume    = {143},
  journal   = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr},
  number    = {22},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0021-9606},
  doi       = {10.1063/1.4938051},
  pages     = {1},
  year      = {2015},
  language  = {en}
}