For the first time, researchers place an electron in a dual state—neither freed nor bound

Atoms are composed of electrons moving around a central nucleus to which they are bound. The electrons can also be torn away via the powerful electric field of a laser, overcoming the confining force of their nucleus. A half-century ago, the theorist Walter Henneberger wondered if it were possible to use a laser field to free an electron from its atom without removing it from the nucleus. Many scientists considered it to be impossible. However, it has now been successfully confirmed by physicists from the University of Geneva (UNIGE), Switzerland, and the Max Born Institute (MBI) in Berlin, Germany.

For the first time, researchers controlled the shape of the laser pulse to keep an electron both free and bound to itsnucleus, and were at the same time able to regulate the electronic structure of the atom. What's more, they also made these unusual states amplify laser light and identified a no-go area. In this area, nicknamed "Death Valley," the physicists lost all their power over the electron. These results shatter the usual concepts related to the ionisation of matter. The results have been published in the journal Nature Physics.

Henneberger's hypothesis proposed that if an electron were trapped in the laser, it would be forced to pass back and forth in front of its nucleus, and would thus be exposed to the electric field of both the laser and the nucleus. This dual state would make it possible to control the motion of electrons exposed to both electric fields, and would let the physicists create atoms with a new electronic structure tunable with light.