Physicists track electrons as they tunnel to freedom

Every year in the depths of winter, Dutch physicists make a pilgrimage to the south. There, at a sprawling, maze-like hotel, they get together to drink and dis each other's work at the annual Physics@FOM conference. This year is no different, and, like the rest of my colleagues, I am blowing off an afternoon session in order to report on some of the more interesting work being presented.

As usual, the tone and quality of any conference is dominated by its plenary speakers—especially the opening speaker. This year, Physics@FOM (FOM is the Dutch funding agency for fundamental physics) invited Ursula Keller, a pioneer in the field of ultrafast spectroscopy (using extremely short light pulses to probe the nature of matter), to give the opening lecture.

Her work has, among other things, focused on determining how fast quantum tunneling takes place. Specifically, she looks at a particular problem: if you apply a very strong light pulse to an atom, the electric field of the light pulse almost overpowers the attraction between the nucleus and the electron, allowing the electron to tunnel to freedom. But, how long does it take for an electron to break free of a nucleus? And how far away from the nucleus does an electron have to be before it is actually free?