M. Ossiander, M. Schultz

Scientists Have Measured The Smallest Fragment of Time Ever

We just witnessed an electron escaping an atom.

14 NOV 2016

Our understanding of time and the world around us just got way more precise. Physicists have successfully measured changes in an atom on the level of zeptoseconds. That's a trillionth of a billionth of a second - the smallest fragment of time ever observed.

With this new level of detail, they were able to measure the entire process of an electron escaping its atom for the first time, in a stunning test of Einstein's photoelectric effect.


The photoelectric effect was first proposed by Albert Einstein in 1905, and occurs when particles of light, known as photons, strike the electrons orbiting an atom.

According to quantum mechanics, the energy from these photons is either absorbed entirely by one electron, or divided among a few of them. But until now, no one has been able to study this process in enough detail to know for sure how it's decided.

The end result is that an electron is sent flying from the bonds of its parent atom in an incredibly rapid process. Previous research has shown that the whole thing from start to finish takes between 5 and 15 attoseconds (10-18 seconds).

But before this, researchers had only been able to measure in detail what happened after the electron fled its atom.

Now a team led by the Max Planck Institute of Quantum Optics in Germany has been able to see the other side of the process for the first time - and measure what happens in the tiny amount of time before the electron leaves the atom.

They did this by firing a range of lasers at a helium atom, and were able to measure the entire photoelectric effect with zeptosecond (10-21 seconds) precision - the smallest fragment of time ever measured.


"Using this information, we can measure the time it takes the electron to change its quantum state from the very constricted, bound state around the atom to the free state," one of the researchers, Marcus Ossiander, told Rebecca Boyle over at New Scientist.

The team picked helium atoms to study because they have just two electrons, which means they're complex enough that the researchers were able to measure their quantum mechanical behaviour - how the photon's energy was split between the electrons - but simple enough that they could spot some patterns in the results.

In the first set of experiments, the team fired a super-short, extremely ultraviolet laser pulse at a helium atom to excite its two electrons.

The pulse lasted just 100 to 200 attoseconds, but by making a whole lot of readings across that time and calculating their statistical spread, the team was able to narrow events down to a time frame of 850 zeptoseconds.

They then used a near-infrared laser pulse, which lasted 4 femtoseconds (10-15 seconds). Overall, they calculated that the ejection of an electron took between 7 and 20 attoseconds, depending on how the electron interacted with the nucleus and the other electron.

That meant the researchers were able to finally get some insight into how the electrons divided up the laser's energy.

Sometimes the energy was split evenly between the two, sometimes it was uneven. And sometimes, one electron took all of the energy. 

There were several factors that influenced the divide, including the correlation between the electrons, and the electromagnetic state of the laser field.

There's still more work to be done, but this is an exciting step towards finally understanding the quantum behaviour of atoms - and how electrons work on an individual basis.

Once we properly understand how these fundamental building blocks of matter function, it'll help improve future technologies, such as superconductivity and quantum computing

Now the team will attempt to conduct more experiments to create a full description of how these electrons behave when exposed to a photon's energy. 

"There is always more than one electron. They always interact. They will always feel each other, even at great distances," lead researcher Martin Schultze told 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."

The research has been published in Nature Physics.

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