Coherent control of strongly driven quantum dynamics using FERMI shaped pulses

The interaction of light with matter provides indispensable insight into the quantum mechanical world of atoms and molecules on their intrinsic time and length scale. Compared to the macroscopic world, these scales are extreme: about 10 fs for the motion of the nuclei, about 10 as for the motion of the electrons; 0.2 nm is the typical length of a chemical bond. A major objective in science is the control of the nanoscopic processes on their extreme scales, which remains a challenge. Based on the concepts of quantum mechanics, specially tailored light fields can be used to address this problem. Here, the electromagnetic wave-character of light is exploited. By shaping the amplitude, phase and polarization of the electromagnetic waves, fields can be sculpted that enhance certain quantum processes while suppressing others, resulting in a net control of the system. The prerequisite is the ability to shape the electromagnetic field of ultrashort laser pulses with durations of just a few femtoseconds. Such pulses enabled scientists for the first time to trigger and control the atomic and molecular processes on their natural time scale.

In the visible range of the spectrum the spectro-temporal shaping of ultrashort laser pulses is a mature technique. Potential applications can be found in physics, chemistry and material science, for instance in the control of chemical reactions, efficient qubit manipulation, the exploration of complex reaction pathways, and the emergence of new spectroscopy concepts. To date, corresponding concepts in the extreme ultraviolet (XUV) and X-ray regime are hardly explored. The short-wavelength domain provides a perspective to access shorter time and length scales. Extremely short laser pulses with attosecond duration are available in this range, and highly localized inner-shell electrons can be addressed at these photon energies. Thus, extending spectro-temporal pulse shaping to the short-wavelength regime promises the quantum control of matter on unprecedented short time scales and with chemical sensitivity.

Figure 1: Quantum control of the strongly driven dynamics in helium atoms. Left: level scheme. Right: photoelectron spectrum showing the split-up of the energy level in helium and the control of the relative population by shaping the phase of the XUV pulses. Adapted from the original paper, licensed under a Creative Commons Attribution 4.0 International License, see: http://creativecommons.org/licenses/by/4.0/.

In this study, a key step towards this development is achieved: the control of quantum dynamics by the shaping of XUV pulses is established. The concept is applied to a fundamental problem, that is, the control of the quantum dynamics in a strongly driven few-electron system. To this end, helium atoms are irradiated with highly intense XUV pulses produced by one of the two advanced light sources operated by Elettra – Sincrotrone Trieste: the free electron laser FERMI. If an atom (or any other quantum system) is exposed to intense fields, the energy levels of the electrons start to shift or even split up into multiple states. Under these conditions, the quantum dynamics of the system have to be described by coupled electron-photon states, so called “dressed states”. In the experiment, carried out at the LDM beamline of FERMI, these hybrid states exist only in an ultrashort time window during the perturbation of the system by the light pulse. The ultrafast dynamics of these short-lived states are successfully controlled by shaping the phase of the XUV laser pulses (Figure 1). These results are a fundamental demonstration that quantum control using shaped laser fields can be indeed extended to the short-wavelength domain. This opens an exciting route towards the exploration and control of matter with unprecedented capabilities.

Fabian Richter¹, Ulf Saalmann², Enrico Allaria³, Matthias Wollenhaupt⁴, Benedetto Ardini⁵, Alexander Brynes³, Carlo Callegari³, Giulio Cerullo⁵, Miltcho Danailov³, Alexander Demidovich³, Katrin Dulitz⁶, Raimund Feifel⁷, Michele Di Fraia^3,8, Sarang Dev Ganeshamandiram¹, Luca Giannessi^3,9, Nicolai Gölz¹, Sebastian Hartweg¹, Bernd von Issendorff¹, Tim Laarmann^10,11, Friedemann Landmesser¹, Yilin Li¹, Michele Manfredda3, Cristian Manzoni¹², Moritz Michelbach¹, Arne Morlok¹, Marcel Mudrich¹³, Aaron Ngai¹, Ivaylo Nikolov³, Nitish Pal³, Fabian Pannek¹⁴, Giuseppe Penco³, Oksana Plekan³, Kevin C. Prince³, Giuseppe Sansone¹, Alberto Simoncig³, Frank Stienkemeier¹, Richard James Squibb7, Peter Susnjar³, Mauro Trovò³, Daniel Uhl¹, Brendan Wouterlood¹, Marco Zangrando^3,8, and Lukas Bruder¹

¹ Institute of Physics, University of Freiburg, Freiburg, Germany
² Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany
³ Elettra-Sincrotrone Trieste S.C.p.A., Trieste, Italy
⁴ Institute of Physics, University of Oldenburg, Oldenburg, Germany
⁵ Dipartimento di Fisica, IFN-CNR, Milan, Italy
⁶ Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
⁷ Department of Physics, University of Gothenburg, Gothenburg, Sweden
⁸ Istituto Officina dei Materiali, CNR (CNR-IOM), Trieste, Italy
⁹ Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, Frascati, Italy
¹⁰ Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
¹¹ The Hamburg Centre for Ultrafast Imaging CUI, Hamburg, Germany
¹² IFN-CNR, Milan, Italy
¹³ Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
¹⁴ Institute for Experimental Physics, University of Hamburg, Hamburg, Germany

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