Featured Research

from universities, journals, and other organizations

Electrons Caught In The Act Of Tunnelling

Date:
April 12, 2007
Source:
Max Planck Society
Summary:
An international team of researchers has observed the quantum mechanical tunnelling effect for the first time.

There are two ways of conquering a mountain. In classical physics, one must climb the mountain to get to the other side. That is not the case in quantum physics: objects can simply cross the mountain horizontally - by tunnelling through it.
Credit: Max Planck Institute for Quantum Optics

We have to climb a mountain in order to conquer it. In quantum physics there is a different way: objects can reach the opposite side of a hill simply by tunnelling through it, instead of laboriously climbing over it. An international team of researchers working with Prof. Ferenc Krausz from the Max Planck Institute for Quantum Optics has now observed electrons in this tunnelling process. This effect is responsible for the ionization of atoms under the influence of strong magnetic fields.

The electrons overcome the attraction of the atomic nucleus by tunnelling through a potential wall. The scientists used ultra-short laser pulses to show discrete stages of ionization in this process, each of which lasts 100 attoseconds - a fraction of a billionth of a second. The results make a significant contribution to understanding how electrons move around in atoms and molecules.

In the same way as gravity brings a body to a halt on the floor of a valley, the nuclear force (which binds protons and neutrons to form the atomic nucleus) and the electrical force (which combines negatively charged electrons with the positively charged atomic nucleus to make an atom) hold these particles within a tiny space. This binding effect can also be depicted as a type of valley, which is also called a potential by physicists. In the world of quantum particles, it is, to a certain extent, a normal event to tunnel through the wall surrounding the potential well.

An international team of researchers working with Ferenc Krausz has now caught the electrons in the act of tunnelling through the binding potential of the atom nucleus under the influence of laser light. The physicists used the new tools provided by attosecond metrology. "For the first time, our findings confirmed in real time observation the theoretical predictions of quantum mechanics," says Ferenc Krausz, Director at the Max Planck Institute for Quantum Optics and head of the team of scientists.

The tunnelling effect can be explained by the wave behaviour of each particle. Macroscopic objects are extremely unlikely to tunnel, which is why the phenomenon has never been observed in them. In contrast, there is a significant probability that particles from the microcosmos will tunnel through areas where, according to the rules of traditional physics, they are not even supposed to be. The tunnelling effect is considered to be responsible for processes as varied as atomic nuclei decay and the switching process in electronic components. However, since it only lasts for an extremely short time, it has not yet been observed in real time.

Krausz and his colleagues have now followed this process live with the aid of two light pulses: an intense pulse of just a few wave trains of red laser light and an attosecond pulse of extreme ultraviolet light perfectly synchronized with the red pulse. The electrical field of the laser pulses periodically exerts strong forces on the electrons. When the force is at its strongest, the light force presses the potential wall downwards. For a short moment when the wave peaks, the electron has the opportunity to penetrate the barrier and escape from the atom. This opportunity only arises when the wave peaks, that is over an extremely short interval of a fraction of a femtosecond, a trillionth of a second.

There is no instrument that can directly resolve the tunnel effect. It is only possible to show the existence of the end products, the atoms, which, following the laser pulse, disintegrate into an electron and a positively charged ion. The researchers therefore had to use the trick of experimenting with neon atoms. In these, the electrons are in a closed shell, and therefore in particularly strong bonds, and resist the attempts of the laser pulse to release them from the atom. Only electrons hit by an attosecond flash of UV manage to reach the periphery of the atom and can extricate themselves from the atom by tunnelling. Therefore, the physicists can only ionize neon atoms with a red laser pulse that they have first prepared with this flash.

"With a UV pulse lasting just 250 attoseconds, which was synchronized exactly with the red laser pulse, we moved an electron at any point in time during the laser wave with attosecond precision to the periphery," explains Krausz. Step by step, the researchers shifted this point in time and measured the number of atoms ionized by the laser. This allowed them to reconstruct the chronology of the ionization process. As the theory predicted, the electrons left the atoms in the immediate vicinity of the most intense wave peaks, which can be seen clearly from the discrete stages of ionization coinciding exactly with the peaks in fig. 3 (the green line). The electrons remained at this stage for less than 400 attoseconds. Within such a short period, the electrons are released from the atom by the light energy.

Original work: M. Uiberacker, Th. Uphues, M. Schultze, A. J. Verhoef, V. Yakovlev, M. F. Kling, J. Rauschenberger, N. M. Kabachnik, H. Schrφder, M. Lezius, K. L. Kompa, H.-G. Muller, M. J. J. Vrakking, S. Hendel, U. Kleineberg, U. Heinzmann, M. Drescher und F. Krausz "Attosecond real-time observation of electron tunnelling in atoms" (Nature, 5 April 2007)


Story Source:

The above story is based on materials provided by Max Planck Society. Note: Materials may be edited for content and length.


Cite This Page:

Max Planck Society. "Electrons Caught In The Act Of Tunnelling." ScienceDaily. ScienceDaily, 12 April 2007. <www.sciencedaily.com/releases/2007/04/070412131304.htm>.
Max Planck Society. (2007, April 12). Electrons Caught In The Act Of Tunnelling. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2007/04/070412131304.htm
Max Planck Society. "Electrons Caught In The Act Of Tunnelling." ScienceDaily. www.sciencedaily.com/releases/2007/04/070412131304.htm (accessed July 23, 2014).

Share This




More Matter & Energy News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) — 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com
Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) — Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
Powered by NewsLook.com
Europe's Car Market on the Rebound?

Europe's Car Market on the Rebound?

Reuters - Business Video Online (July 23, 2014) — Daimler kicks off a round of second-quarter earnings results from Europe's top carmakers with a healthy set of numbers - prompting hopes that stronger sales in Europe will counter weakness in emerging markets. Hayley Platt reports. Video provided by Reuters
Powered by NewsLook.com
9/11 Commission Members Warn of Terror "fatigue" Among American Public

9/11 Commission Members Warn of Terror "fatigue" Among American Public

Reuters - US Online Video (July 22, 2014) — Ten years after releasing its initial report, members of the 9/11 Commission warn of the "waning sense of urgency" in combating terrorists attacks. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins