Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Relativistic tunnelling

17.04.2013
The time a particle takes to tunnel through a barrier in quantum mechanics is obviously longer than many physicists assumed so far. Scientists at the Max Planck Institute for Nuclear Physics in Heidelberg showed evidence that tunnelling takes a very brief but finite and measureable time.

This is the result of their theoretical study on an electron that tunnels out of an atom in an intense laser field while being accelerated up near to the speed of light.


Fig. 1: Schematic description of tunnel ionization of highly charged ions at relativistic laser intensities. The superposition of the Coulomb potential of the atomic core and the electric field of the laser forms a potential barrier (in blue) that the electronic wave packet (in green) may tunnel through into the direction of the laser's electric component. Unlike in nonrelativistic tunnelling the ionization potential (in red) becomes position-dependent as a consequence of the laser's magnetic field. Furthermore, while tunnelling the wave packet gets shifted under the influence of ‘light pressure’ into the propagation direction fields (solid green line, see text for details).

A ball running uphill will not roll over the hill if it is not given enough velocity. On atomic scales that are ruled by the laws of quantum physics, however, a particle has a non-zero chance to get onto the opposite side of a barrier even though it is not allowed to get over according to classical physics. Physicists call this effect tunnelling because it seems as if the particle forms a tunnel to pass through the barrier.

A quantum tunnelling barrier may be build up in an atom or a hydrogen-like ion by the attractive Coulomb forces that attach the electron to the atomic core and the electric field of a strong laser that pulls the electron away from the core. Metaphorically speaking the ion's Coulomb potential and the laser's electric field form a hill (a so-called potential barrier) the electron may tunnel through to ionize. For highly charged hydrogen-like ions, i.e., an atomic core with a single electron, however, ultra-strong lasers with intensities of the order of 10^18 W/cm^2 and above are required to achieve measureable ionization probabilities. Such ultra-strong lasers can no longer be treated as pure electric fields, the laser's magnetic field component has to be taken into account, too. Magnetic fields, however, do not fit into the conventional picture of a tunnelling barrier.

Therefore, it has been argued that the whole tunnelling concept may break down in the presence of magnetic fields. In Physical Review Letters, Klaiber and colleagues at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, have shown now that the notion of a tunnelling barrier can also be applied in the presence of magnetic fields of ultra-strong lasers via reshaping the potential barrier. A question that has caused many controversial discussions among physicists and remains unsolved till today is how long an electron needs to tunnel through a barrier.

Direct measurements of tunnelling times are hampered by experimental as well as conceptual difficulties. While extending the tunnelling picture into the regime of ultra-strong lasers, Klaiber and colleagues demonstrated that tunnel ionization of hydrogen-like ions via ultra-strong lasers features two time scales which may be measured indirectly. In particular, a small shift of the point of exit where the electron leaves the tunnelling barrier is caused by the presence of a magnetic field. This shift is proportional to the so-called Eisenbud-Wigner-Smith tunnelling time.

Furthermore, the magnetic field changes the velocity distribution of the ionized electrons. Ionized electrons escape with a non-zero velocity along the propagation direction of the laser that is proportional to the so-called Keldysh tunnelling time. Thus, Max-Planck-physicists related these two tunnelling times to quantities that are accessible to direct measurements in laboratory experiments. For tunnel ionization of hydrogen-like ions with small atomic numbers lasers of moderate intensities and, therefore, weak magnetic components are sufficient and the consequences of the two tunnelling time scales become small.

This may explain why experimentalists have not been able so far to measure non-zero tunnelling times in tunnelling through high barriers. By increasing the laser's intensity the height of the tunnelling barrier decreases and the shape of the barrier changes qualitatively. First calculations have given hints that in this regime the tunnelling times become relevant again and may be determined experimentally.

Original publication:
Under-the-barrier dynamics in laser-induced relativistic tunneling
Michael Klaiber et al., Phys. Rev. Lett. 110, 153004 (2013)
doi:10.1103/PhysRevLett.110.153004

Contact:

Hon.-Prof. Dr. Christoph H. Keitel
Phone: (+49)6221 516-150
E-Mail: christoph.keitel@mpi-hd.mpg.de

Dr. habil. Karen Z. Hatsagortsyan
Phone: (+49)6221 516-160
E-Mail: Karen.Hatsagortsyan@mpi-hd.mpg.de
Weitere Informationen:
http://link.aps.org/doi/10.1103/PhysRevLett.110.153004
Original publication
http://www.mpi-hd.mpg.de/keitel/
Division Keitel at MPIK

Dr. Bernold Feuerstein | Max-Planck-Institut
Further information:
http://www.mpi-hd.mpg.de

More articles from Physics and Astronomy:

nachricht First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>