In the media. Quantum physics: exceptional measurement of 'Rabi oscillations' using the FERMI laser

The results of the experiment published in Nature. This and the great potential of Free Electron Lasers are being discussed at the ongoing FEL2022 International Conference in Trieste, which closes on 26 August

The periodic pattern with which the electrons of atoms exchange energy with laser radiation has been known since the theory was first presented in 1955 by Autler and Townes. The phenomenon, referred to as 'Rabi oscillations', has since then been experimentally observed in the most diverse areas of physics, but only for long-wavelength radiation, and this is still a key observation in understanding radiation-matter interaction.

Today, new research by a pool of researchers from various nationalities and institutes has made it possible to observe the manifestation of such oscillations on a scale ten times smaller than before. The results were published in the prestigious scientific journal Nature.

The article, published on 17 August, with Saikat Nandi of the Lumiere Matiere Institute in Lyon as first author, involved 29 researchers from Italy, France, Sweden and Germany. The high-intensity laser pulses required for the experiment were generated by the FERMI free-electron laser at the Elettra Sincrotrone Trieste research centre.

The coordinated oscillation of electron and laser radiation can be compared to a child jumping rope. When the child is in the air, the electron is in a so-called excited state, while when the child is on the ground, the electron is in the fundamental state (in English, 'ground state', where 'ground' literally means 'ground'). The energy of the laser field oscillates, just like a jump rope, and forces the electron to 'jump'.

"The experimental novelty is that Rabi's oscillations were measured at wavelengths ten times shorter than ever before, and this was made possible by FERMI's ultra-bright light, to date the only source in the world to possess the required spectral purity," says Carlo Callegari, head of the 'Low Density Matter' experimental station where the measurements were carried out.

FERMI is the Free-Electron Laser operated by Elettra Sincrotrone Trieste, an extremely innovative laser consisting of a 350-metre underground structure and based on a linear electron accelerator, which has been operational for users since 2012: it is a unique excellence for the area in which it operates and for Italy, and competes globally with all the countries that are investing today to be at the forefront of scientific research in the most diverse fields of science.

It was possible to conduct the experiment thanks to FERMI's unique characteristics, and the team of Italian researchers contributed to the set-up of the machine, the experimental station, and the collection of data. The results obtained pave the way for similar measurements on virtually all atoms and molecules.

These days, from 22 to 26 August, the TCC Trieste Convention Centre is hosting the FEL2022 International Conference, the 40th edition of the International Conference dedicated to free-electron lasers (FEL stands for Free-Electron laser), the annual congress of the leading experts on these lasers, which represent one of the most advanced expressions of light source technology.

The conference, which was postponed last year due to the pandemic, this year celebrates its 40th edition and the arrival of around 300 participants including researchers and related companies from all over the world. Organised and promoted by Elettra Sincrotrone Trieste, at the helm of which Prof. Alfonso Franciosi, President and CEO, has been firmly during these important years of development, the conference not only provides intense days of scientific discussion, but also allows 150 of the best scientists working in other similar institutes to visit FERMI, to grasp the technical specificities and innovations that make it unique in terms of the purity of the light produced.

Trieste and its system are once again confirmed as being at the top of the world in terms of scientific research, the number of projects and publications, and the ability to attract the best brains of the future.