Registration Room: AlbaNova Main Entrance

Welcome! Room: FR4, Oskar Klein Auditorium

Spectroscopy with attosecond time resolution

• Ferenc Krausz (MPI Garching)

Room: FR4, Oskar Klein Auditorium Electronic motion is a key process in a wide range of modern technologies, including micro- to nano-electronics, photovoltaics, bioinformatics, molecular biology, and medical as well as information technologies. The atomic-scale motion of electrons typically unfolds within tens to thousands of attoseconds (1 attosecond [as] = 10^-18 s). Recent advances in laser science have opened the door to watching and controlling these hitherto inaccessible microscopic dynamics [1]-[14]. Key tools include waveform-controlled few-cycle laser light and attosecond extreme ultraviolet pulses. They permit control of atomic-scale electric currents just as microwave fields control currents in nanometer-scale semiconductor chips. By analogy to microwave electronics, we have dubbed this new technology "lightwave electronics" [10,12]. Lightwave electronics provides - for the first time - real-time access to the motion of electrons on atomic and sub-atomic scales. Insight into and control over microscopic electron motion are likely to be important for developing brilliant sources of X-rays, understanding molecular processes relevant to the curing effects of drugs, the transport of bioinformation, or the damage and repair mechanisms of DNA, at the most fundamental level, where the borders between physics, chemistry and biology disappear. Once implemented in condensed matter, the new technology will be instrumental in advancing electronics and electron-based information technologies to their ultimate speed: from microwave towards lightwave frequencies.<br> [1] M. Hentschel et al., Nature 414, 509 (2001) <br> [2] R. Kienberger et al., Science 291, 1923 (2002)<br> [3] A. Baltuska et al., Nature 421, 611 (2003)<br> [4] R. Kienberger et al., Nature 427, 817 (2004)<br> [5] E. Goulielmakis et al., Science 305, 1267 (2004)<br> [6] M. Drescher et al., Nature 419, 803 (2002)<br> [7] M. Uiberacker et al., Nature 446, 627 (2007)<br> [8] M. Kling et al., Science 312, 246 (2006)<br> [9] A. Cavalieri et al., Nature 449, 1029 (2007)<br> [10] E. Goulielmakis et al., Science 317, 769 (2007)<br> [11] E. Goulielmakis et al., Science 320, 1614 (2008)<br> [12] F. Krausz, M. Ivanov, Rev. Mod. Phys. 81, 163 (2009). <br> [13] M. Schultze et al., Science 328, 1658 (2010). E. Goulielmakis et al., Nature 466, 739 (2010).

Attosecond Physics using Attosecond pulse trains

• Anne L'Huillier (Lund University)

Room: FR4, Oskar Klein Auditorium

Ultra-fast dynamics: Pump-Probe Experiments at FELs

• Joachim Ullrich (MPI Heidelberg)

Room: FR4, Oskar Klein Auditorium

The Reincarnation of Multiphoton Processes

• Peter Lambropoulos (University of Crete)

Room: FR4, Oskar Klein Auditorium About fifty years ago, the first laser-induced two-photon absorption in an atomic vapor was observed in Cesium. With the subsequent developments in laser technology, the field of multiphoton (MP) processes evolved through a series of stages, involving harmonic generation, resonantly enhanced multiphoton ionization (REMPI), effects of field correlations in non-linear processes, to mention a few. With the advent of sub-picosecond, Fourier limited and eventually few-cycle sources, over the last 20 years, the paradigm shifted to what is now known as strong field phenomena and attosecond physics, in terms of the single-active electron approximation, dominated by recollision dynamics. Thus multiphoton processes per se went into a dormant stage, leaving behind certain tools such as REMPI. The appearance of strong, sub-picosecond, radiation in a broad frequency range, from the XUV to hard X-rays, has now revived MP concepts and techniques, but in an entirely new context. Whereas traditional MP processes under infrared to UV radiation involved exclusively valence electrons, in the new paradigm it is inner electrons that dominate the chain of events triggered by the exposure to strong, short wavelength radiation. <br> <br> After a brief historical review of the main stages and concepts of MP processes under long wavelength radiation, I discuss their connection to the short wavelength context, using specific examples of observations in the XUV to soft X-ray range, in order to illustrate the similarities and differences between the two paradigms. In particular the operational meaning of concepts such as strong field, short pulse, sequential versus direct multiple ionization, double resonance, etc. are discussed and illustrated through the application to specific systems.

Attosecond molecular spectroscopies with XUV harmonic radiation

• Alfred Maquet (UPMC Paris)

Room: FR4, Oskar Klein Auditorium

Hole dynamics and coherence

• Robin Santra (DESY Hamburg)

Room: FR4, Oskar Klein Auditorium Photoionization of an atom or a molecule leads, in general, to the formation of a superposition of ionic eigenstates. That superposition cannot, in general, be described in terms of a wave function, but a description in terms of a reduced density matrix (a statistical mixture) is required. In the first part of the talk, ultrafast, partially coherent hole dynamics driven by spin-orbit coupling will be analyzed in terms of a time-dependent multichannel mean-field theory [1]. This theory will be compared with the results of an attosecond transient absorption experiment on strong-field-ionized krypton atoms [2]. In the second part of the talk, a new implementation of time-dependent configuration interaction singles (TDCIS) will be discussed [3]. Using TDCIS calculations, it will be shown that photoelectron-mediated interchannel coupling causes ion decoherence in attosecond photoionization. As a consequence, even if the spectral bandwidth of the ionizing pulse exceeds the energy splittings among the hole states involved, perfectly coherent hole wave packets cannot be formed [4] <br> <br> [1] N. Rohringer and R. Santra, Phys. Rev. A 79, 053402 (2009). <br> [2] E. Goulielmakis, Z.-H. Loh, A. Wirth, R. Santra, N. Rohringer, V. S. Yakovlev, S. Zherebtsov, T. Pfeifer, A. M. Azzeer, M. F. Kling, S. R. Leone, and F. Krausz, Nature 466, 739 (2010). <br> [3] L. Greenman, P. J. Ho, S. Pabst, E. Kamarchik, D. A. Mazziotti, and R. Santra, Phys. Rev. A 82, 023406 (2010). <br> [4] S. Pabst, L. Greenman, P. J. Ho, D. A. Mazziotti, and R. Santra, Phys. Rev. Lett. 106, 053003 (2011). <br>

Analysis and control of electronic motion in the time domain

• E. K. U. Gross (MPI Halle)

Room: FB53 This lecture is about how electronic motion can be monitored, analyzed and, ultimately, controlled, in real time. In particular: (i) A novel approach to describe electronic transport through single molecules or atomic wires, sandwiched between semi-infinite leads, will be presented. The basic idea is to propagate the time-dependent Kohn Sham equations in time upon ramping up a bias between the metallic leads. In this way, genuinely time-dependent phenomena, not accessible in the standard Landauer approach, can be addressed. For example, employing an Anderson model, we demonstrate that Coulomb blockade corresponds, in the time-domain, to a periodic charging and discharging of the quantum dot [1]. (ii) With modern pulse-shaping facilities, the control of electronic motion is becoming more and more realistic. By combining quantum optimal control theory with TDDFT, we calculate shaped laser pulses suitable to control, e.g., the chirality of currents in quantum rings [2], the location of electrons in double quantum dots, as well as the enhancement of a single peak in the harmonic spectrum of atoms and molecules. (iii) In all practical TDDFT calculations, approximate forms of the exchange-correlation potential need to be employed. One of the most popular approximations, the adiabatic local-density approximation (ALDA) will be analyzed as to whether the main error comes from the adiabaticity assumption, i.e. locality in time, or from the LDA, i.e. locality in space. For an exactly solvable model where the exact adiabatic approximation can be extracted, we find the surprising fact, that the adiabaticity assumption can be an excellent approximation even in highly intense laser fields [3]. (iv) Finally, the coupling between electronic and nuclear motion will be addressed. As a first step towards a full ab-initio treatment of the coupled electron-nuclear motion in time-dependent external fields, we deduce an exact factorization of the complete wavefunction into a purely nuclear part and a many-electron wavefunction which parametrically depends on the nuclear configuration. We derive formally exact equations of motion for the nuclear and electronic wavefunctions [4]. These exact equations lead to a rigorous definition of time-dependent potential energy surfaces as well as time-dependent geometric phases. With the simple example of the hydrogen molecular ion in a laser field we demonstrate the significance of these concepts in understanding the full electron-ion dynamics. In particular, the time-dependent potential energy surfaces are shown to represent a powerful tool to analyse and interpret different (direct vs. tunneling) types of dissociation processes. [1] S. Kurth, G. Stefanucci, E. Khosravi, C. Verdozzi, E.K.U. Gross, Phys. Rev.Lett.104, 236801 (2010). [2] E. Räsänen, A. Castro, J. Werschnik, A. Rubio, E.K.U. Gross, Phys. Rev. Lett. 98,157404 (2007). [3] M. Thiele, E.K.U. Gross and S. Kümmel, Phys. Rev. Lett. 100, 153004 (2008). [4] A. Abedi, N.T. Maitra, E.K.U. Gross, Phys. Rev. Lett. 105, 123002 (2010).

Read-out and coherent control of electron spin qubits in quantum dots

• Lieven Vandersypen (TU Delft)

Room: FB53 Quantum information processing requires accurate control of the time evolution of physical systems at the level of single quantum mechanical degrees of freedom. I will present our work on the coherent manipulation of individual and coupled electron spins in semiconductor quantum dots, and on independent read-out of the spins.

Exploring few- and many-body physics with frozen Rydberg gases

• Matthias Weidemüller (University of Heidelberg)

Room: FB53 The investigation of Rydberg atoms has a long history, dating back to the early days of Atomic Physics. Rydberg gases at ultra-low temperatures were first realized only in the last decade by combining advances in atom manipulation and cooling with narrow-band laser excitation of Rydberg states. The exquisite controlof the electronic excitation and the centre-of-mass motion, employing external fields, allows one to exploit the unique and exaggerated properties of Rydberg atoms, namely their large size, large electronic orbiting times, small electronic binding energy, and extremely strong dipole–dipole and van derWaals interactions. The combination of strong atomic interactions and a high level of quantum control, reaching down to the single atom level, gives rise to both new fundamental physics and interesting applications of Rydberg gases, including for example investigations of novel phases of quantum matter, and controlled preparation of atom or photon entanglement. In my presentation I will give a general introduction into the field and discuss some recent experiments of my group.

Talk by Luca Argenti: Vibrationally resolved photoelectron spectroscopy of CH4: Studying electron diffraction from within Room: Nordita building

Talk (Jan Michael Rost)

Talk by Tobias Kramer: The quantum-classical borderline, from 2 to many electrons

Talk by Michael Genkin: Transport through Rydberg aggregates in the blockade regime We discuss excitation dynamics in Rydberg aggregates, induced by resonant dipole-dipole interactions. In particular, we investigate the possibility to extend recently suggested efficient single-atom transport schemes to Rydberg-blocked atomic clouds.

Talk by Maria Richter: Photoelectron spectroscopy of the Kramers-Henneberger atom Today laser pulses with electric fields comparable to or higher than the electrostatic forces binding valence electrons in atoms and molecules have become a routine tool with applications in laser acceleration of electrons and ions, generation of short wavelength emission from plasmas and clusters, laser fusion, etc. Intense fields are also naturally created during laser filamentation in the air or due to local field enhancements in the vicinity of metal nanoparticles. One would expect that very intense fields would always lead to fast ionization of atoms or molecules. However, recently observed acceleration of neutral atoms [1] at the rate of 1015 m/sec2 when exposed to very intense infrared (IR) laser pulses demonstrated that a substantial fraction of atoms remained stable during the pulse. What is the structure of these exotic laser-dressed atoms surviving super-atomic fields? Can it be directly imaged using modern experimental tools? Using ab-initio calculations for the potassium atom, we show [2] how the electronic structure of these stable "laser-dressed" atoms can be unambiguously identified and imaged in angle resolved photoelectron spectra obtained with standard femtosecond laser pulses and velocity map imaging techniques, see e.g. recent experiments [3,4]. We find that the electronic structure of these atoms follows the theoretical predictions made over 40 years ago by W. Henneberger [5], that have so far remained unconfirmed experimentally and thus not generally accepted. We also show that the so-called Kramers-Henneberger (KH) atom is formed and can be detected even before the onset of the stabilization regime. Our findings open the way for visualizing and controlling bound electron dynamics in strong laser fields and reexamining its role in various strong field processes, including the microscopic description of high order Kerr non-linearities and their role in laser filamentation [6]. 1. Eichmann et al., “Acceleration of neutral atoms in strong short-pulse laser fields”, Nature, 461, 1261-1264 (2009). 2. Felipe Morales, Maria Richter, Serguei Patchkovskii and Olga Smirnova, “Imaging the Kramers-Henneberger atom”, PNAS, accepted. 3. M. Wollenhaupt, M. Krug, J. Köhler, T. Bayer, C. Sarpe-Tudoran and T. Baumert, “Photoelectron angular distributions from strong-field coherent electronic excitation”, Appl. Phys. B, 95, 245 (2009). 4. M. Schuricke, G. Zhu, J. Steinmann, K. Simeonidis, I. Ivanov, A. Kheifets, A. N. Grum-Grzhimailo, K. Bartschat, A. Dorn and J. Ullrich, “ Strong-field ionization of lithium”, Phys. Rev. A, 83, 023413 (2011). 5. W. Henneberger, “Perturbation method for atoms in intense laser fields”, Phys. Rev. Lett., 21, 838 (1968). 6. Béjot et al., “Higher-Order Kerr Terms Allow Ionization-Free Filamentation in Gases”, Phys. Rev. Lett., 104, 103903 (2010).

Talk by Nicolas Sisourat: Giant interatomic Coulombic decay Interatomic Coulombic decay (ICD) is an ultrafast non-radiative electronic decay process for excited atoms embedded in a chemical environment. Via ICD, the excited system can get rid of the excess energy and this excess energy is transferred to one of the neighbors and ionizes it. Whereas the same excited atom when isolated relaxes only by emitting a photon in a time range of picoseconds to nanoseconds, ICD takes place in the femtosecond range. Thus, ICD is generally the most favorable decay process. Through ICD, the energy transfer between the two involved atoms can take place over large distances. A question which arises is how far can atoms exchange energy? The giant extremely weakly bound helium dimer is a perfect candidate to investigate this issue. After simultaneous ionization and excitation of one helium atom, the excited ion can relax through ICD and thus ionize the neighboring neutral helium atom. The resulting two He$^+$ then undergo a Coulomb explosion and fly apart. As it will be shown, the two helium atoms can exchange energy via ICD over distances of more than 45 times their atomic radius. Oscillatory structures in the kinetic energy release spectra reflect the nodal structures of vibrational wavefunctions involved in the decay process.

Talk by Maria Hellgren: Optimal control with time-dependent density-functional theory: First application to the ionization of H2

Talk by Luca Argenti: Towards an interferometric spectroscopy of metastable wave packet dynamics

Talk by Adam Etches: Two-centre interference minima in the high-harmonic generation

Talk by Ken Taylor: The R-Matrix incorporating Time propagation (RMT) method for a multi-electron atom in an intense laser field

Talk by Ingo Barth: Non-adiabatic ionization in circularly polarized laser fields Motivated by the recent experimental work of Goulielmakis et al. on real-time observation of electron motion in the valence 4p shell of krypton atoms [1], we will present the theory for the ionization of arbitrary states of atoms in strong circularly polarized laser fields. It is commonly assumed that strong-field ionization in low-frequency laser field is an adiabatic process. Therefore, one does not expect to generate electronic ring currents in ions during ionization in the low-frequency fields. To check this assumption, we revisit the theory of strong-field ionization developed by Perelomov, Popov, and Terent’ev (PPT) [2,3]. The original PPT theory includes explicit results for ionization of s-orbitals by circularly or in general elliptically polarized laser fields. We extend the PPT approach to p0, p+ and p- orbitals of atoms in circularly polarized field. This allows us to address the question on the asymmetry in ionizing the ring-current carrying p+ and p- orbitals by the right (or left) circular polarization, thus characterizing the currents that can be induced by non-adiabatic ionization. [1] E. Goulielmakis, Z.-H. Loh, A. Wirth, R. Santra, N. Rohringer, V. S. Yakovlev, S. Zherebtsov, T. Pfeifer, A. M. Azzeer, M. F. Kling, S. R. Leone, F. Krausz, Real-time observation on valence electron motion, Nature 466, 739 (2010) [2] A. M. Perelomov, V. S. Popov, M. V. Terent’ev, Ionization of atoms in an alternating electric field, Soviet Physics JETP 23, 924 (1966)

Talk by Armin Scrinzi: What to watch out for when you really do exterior complex scaling

Talk by Ulf Saalmann: Non-adiabatic electron pumps: Rectification and current reversals Adiabatic electron pumps have been theoretically proposed and experimentally realized some time ago. Here, non-adiabatic effects are discussed. It will be shown that one can control the direction of the induced current by changing the driving frequency. This surprising observation is related to a rectification effect in the non-adiabatic regime.

Quantum interferences in attophysics

• Marcus Dahlström (Lund University)

Stark shifts and multielectron polarization effects in atoms and molecules

• Darko Dimitrovski (University of Århus)

Time-dependent description of the electronic predissociation in the LiH molecule

• Patryk Jasik (Gdansk University of Technology)

Reactions involving antihydrogen

• Svante Jonsell (Stockholm University)

Massively parallel ionization in ultra-short pulses

• Ulf Saalmann (MPI Dresden)

Ionization by intense and short electric pulses - classical picture

• Karoly Tokesi

Propagation of strong XFEL pulses

• Faris Gelmukhanov (Stockholm University)

Discussion / Workshops

Simulations on pump and probe experiments on Neon

• Thomas Carette (Stockholm University)

One-and two-photon double ionization of atoms: Identifying the mechanisms

• Morten Førre (University of Bergen)

Accurate numerical methods for explicit time-dependent Hamiltonians

• Hans Karlsson (Uppsala University)

Time scaling with high order time-propagation techniques to solve the time-dependent Schrödinger equation (Part I)

• Johannes Eiglsperger (University of Regensburg)

Time scaling with high order time-propagation techniques to solve the time-dependent Schrödinger equation (Part II)

• Bernard Piraux (Univ. Catholique de Louvain)

Discussion / Workshops

Two-photon double ionization studies in noble gases. A time-dependent density matrix approach of the direct/sequential problem

• Damien Middleton (Dublin City University)

Circular Rydberg states in circularly polarized laser fields

• Sigurd Askeland (University of Bergen)

Electron-energy bunching in laser-driven soft recollisions

• Alexander Kästner (MPI Dresden)

Unbound systems: Studying what remains rather than what escapes

• Sølve Selstø (Oslo University College)

Coherence Distillation

• Alejandro Saenz (Humboldt University Berlin)

Parallel implementation of the TDSE using GPUs

• Cathal O'Broin (Dublin City University)

Discussion / Workshops

Reports from the Nordita Workshop: New findings and directions