FERMI opens up new paths to quantum control: new horizons for atomic and molecular science

In a pioneering experiment conducted at FERMI, the Free Electron Laser (FEL) of Elettra Sincrotrone Trieste, active in Area Science Park, has, for the first time, made it possible to directly control quantum hybrid electron-photon states in helium atoms, demonstrating quantum control of nonlinear electronic dynamics. This significant achievement, the result of international collaboration between theoretical and experimental groups led by Dr Lukas Bruder from the University of Freiburg, involved several Italian institutions: the Polytechnic University of Milan, the Institute of Photonics and Nanotechnologies of the National Research Council in Milan (CNR-IFN), the Istituto Officina dei Materiali of the National Research Council in Trieste (CNR-IOM), the National Institute for Nuclear Physics (INFN), the National Laboratories of Frascati (Rome) and Elettra Sincrotrone Trieste. This is an important milestone in quantum physics, opening up new perspectives for studying and controlling chemical reactions on an atomic scale, thanks also to FERMI’s extraordinary technological capabilities.

The research, published in the scientific journal Nature, demonstrates how precise manipulation of light pulses generated by the FERMI FEL makes it possible to facilitate specific quantum processes, through an approach known as “coherent control”. While this method has been well-established for visible light and at low intensities, it has now been successfully applied to extreme ultraviolet wavelengths, opening up a new field of research for analysing atomic and molecular phenomena occurring on attosecond timescales (one billionth of a billionth of a second).

The FERMI laser stands out on the international scene as the only source of its kind capable of ensuring such precise control of the generation of ultraviolet radiation and X-rays, thanks to the use of an “external seed”. This innovative approach makes it possible to impart further coherence to the light during the amplification process, finally making coherent control experiments feasible. In fact, without this process, amplified radiation would be chaotic and incoherent, with a random sequence of pulses very close to each other.

This experiment exploited ultraviolet radiation pulses with intensities in the range of 10–100 trillion watts per square centimetre, generating quantum states known as “dressed states”, where electrons strongly interact with the light field, altering their energy levels. Thanks to this precise manipulation of the phase and amplitude of these light pulses, the researchers achieved unprecedented control of these dynamics.

The results obtained first of all demonstrate the efficiency and technical maturity achieved by FERMI, since the ability to reproduce effects well known at optical frequencies in X-rays was, and remains, a highly sought-after achievement that can by no means be taken for granted.

Right now, we have new methodologies available for investigating fundamental quantum systems. Very short wavelengths and correspondingly shorter pulse durations generally allow us to handle electrons on their natural length and time scales – i.e. atomic. This also opens up new prospects for developing techniques to control material properties and chemical reactions, with potential implications in sectors such as photovoltaics, catalysis and materials science in general.

When going into such minute details, it becomes increasingly challenging to grasp and understand the events being observed, and these very precise pulses allow us to isolate the smallest details very quickly and with equal precision (as with an ultra-high-resolution camera). Thanks to this technology, it is not only possible to passively explore all these phenomena but also to guide and manipulate them towards new discoveries and new hypotheses.

Institutions involved:

• Institute of Physics, University of Freiburg, Freiburg, Germany
• Max-Planck-Institut für Physik komplexer Systeme, Dresden, Germany
• Elettra-Sincrotrone Trieste S.C.p.A., Trieste, Italy
• Institute of Physics, University of Oldenburg, Oldenburg, Germany Department of Physics, IFN-CNR, Milan, Italy
• Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Innsbruck, Austria
• Department of Physics, University of Gothenburg, Gothenburg, Sweden
• Istituto Officina dei Materiali, CNR (CNR-IOM), Trieste, Italy
• National Institute of Nuclear Physics, National Laboratories of Frascati, Frascati, Italy
• Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany
• The Hamburg Centre for Ultrafast Imaging CUI, Hamburg, Germany
• IFN-CNR, Milan, Italy
• Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
• Institute for Experimental Physics, University of Hamburg, Hamburg, Germany