» Pfeifer » Introduction 

Introduction:

In nature, quantum physics typically dominates on both small length and time scales.  The motion of small particles (e.g. electrons, nuclei) in atoms and molecules, often termed 'quantum dynamics', can thus only be directly observed (and controlled) with tools/probes that are comparable in duration to the characteristic time scales on which their wavefunctions evolve.  This time scale Δt=h/ΔE is the inverse of quantum-mechanical energy-level spacings ΔE.  The latter is typically ΔE~1 eV or larger for electrons in atoms or nuclei in small molecules, corresponding to  a few femtoseconds (ΔE=1 eV<->Δt=4.1 fs=4.1x10^-15 s) or even much shorter, the attosecond region (1 as = 10^-18 s).

It is a long-standing dream of mankind and a quest in fundamental physics, to take snapshots or movies of electron wavefunctions evolving in atoms and molecules.

This dream comes with formidable challenges on the experimental and conceptual side:

While femtosecond and attosecond pulses are now routinely produced in the laboratory, it is mainly the spectroscopic and imaging tools that are underdeveloped.  In addition, conceptually intuitive physical models and frameworks are required to shape and guide our understanding.

It is one of our primary goals to overcome these last but fundamental challenges.  By using experimental methods such as spectral interferometry, multidimensional spectroscopy and coincidence detection of multiple reaction products, we can map out these fast dynamics on their characteristic time scales by measuring both wavefunction amplitude and phase.  Moreover, using controlled coherence properties of our laser systems, we can actively influence and engineer the evolution of quantum waves, creating exotic states of matter that can, in turn, advance our insight into quantum processes and also promise technological applications - e.g. the control of chemical reactions by shaped laser light.

 

Fundamental Scientific Questions:

•

How and how fast do electrons interact with ("talk to") each other?

- electron dynamics on attosecond and few-femtosecond time-scales
- quantum correlation
   –› entanglement — but in natural/"wild-type" systems
       (room-temperature atoms and molecules, "nanotraps")
   –› Coulomb interaction, fermionic symmetry
- by observation, find physically intuitive fundamental pictures of electronic quantum correlation, and electron–electron interaction dynamics

•

What is the quantum-dynamical nature of the chemical bond?

- understand (on a fundamental level) interaction of the chemical bond ("it's what holds it all together", molecules, solids) with light
- understand and control chemical reaction dynamics (making and breaking of bonds)

•

To what extent can multi-electron dynamics be controlled?

- use "perfectly coherent" absolute-phase stabilized light fields (CEP: carrier-envelope phase) to control quasi-classical and quantum dynamics of electrons

- observe the transition from quantum to classical dynamics

- use partially coherent light fields (e.g. free-electron lasers, FELs) to overcome traditional limits

 

Research Techniques and Methods:

Experimental:

  • ultrashort and intense pulsed laser fields
  • attosecond pulse / high-harmonic generation
  • reaction microscopes / COLTRIMS (coincidence particle detectors)
  • multidimensional spectroscopy / spectral interferometry
  • high-resolution spectroscopy
  • laser pulse shaping and control

Theoretical and Modeling:

  • quantum mechanics
  • time-dependent multi-electron Schrödinger equation
  • inter-nuclear and electronic wave-packet propagation
  • propagation of light
  • “creative” modeling of correlation dynamics

 

left: isolated attosecond pulse used for streak-field spectroscopy (Berkeley experiments); right: Generation of Pairs (and Triplets) of Attosecond Pulses, necessary for Interferometry experiments.