Don’t even try to capture a zeptosecond using a run-of-the-mill stopwatch. This tiny slice of time is a fraction of a second—so small it is equal to a single number one sitting 21 places behind the decimal point, a trillionth of a billionth of a second​, reports Rebecca Boyle at New Scientist. And researchers at the Max Plank Institute in Germany finally measured minute changes within an atom on the zeptosecond scale.

The researchers accomplished this feat while studying the so-called photoelectric effect in action. Albert Einstein described this tricky quirk of light in 1905, later winning the Nobel Prize in Physics for his explanation of this defining concept. The photoelectric effect shows that light can act as both a wave and a particle. When a photon, or a particle of light, of a certain energy strikes an electron, it can free the electron from its atom. The photon ejects the electron in a process called photoemission, the basis behind solar energy.

Now researchers have actually captured the electron emission from helium atoms, measuring the minsiscule amount of time it takes for the electron to be ejected after the photon strike. To measure the event, the physicist used a piece of equipment called an Attosecond Streak Camera, which consists of two lasers of different light firing in extremely short bursts, writes Stewart Wills at Optics and Photonics News. The researchers directed the camera toward a jet of helium—a relatively simple gas, consisting of atoms that have only two electrons each.

The first laser was an extremely ultraviolet ray intended to excite the helium enough to relinquish one of its electrons, firing in 100 attosecond pulses (one attosecond is a mere 10-18 seconds). The second laser was near-infrared and was used capture the escaping electrons in action, firing for four femtosecond at a time (a single femtosecond is only 10-15 seconds).

When the helium atom ejected an electron, the infrared laser detected the emission, allowing the researchers to calculate the duration of the event down to 850 zeptoseconds. The experiment showed that it takes between 7 and 20 attoseconds for the helium atom to eject one of its electrons, Boyle reports. The results of the study were published this week in the journal Nature Physics.

The experiment’s results give the researchers some insight into how this quantum process works, writes Boyle, and may one day be useful in quantum computing and superconductivity.

“There is always more than one electron. They always interact. They will always feel each other, even at great distances,” team leader Martin Schultze tells Boyle. “Many things are rooted in the interactions of individual electrons, but we handle them as a collective thing. If you really want to develop a microscopic understanding of atoms, on the most basic level, you need to understand how electrons deal with each other.”

Schultze tells Wills that the team is using helium, one of the simplest atoms, to validate their methods and create measurements for how multiple electrons and photons interact. Working out these tiny timelines with simple atoms is the first step toward understanding more atoms with more electrons.