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 Magnetic nano-imaging on a table top
20.04.2018 | Georg-August-Universität Göttingen

nachricht New record on squeezing light to one atom: Atomic Lego guides light below one nanometer
20.04.2018 | ICFO-The Institute of Photonic Sciences

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: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Tiny microenvironments in the ocean hold clues to global nitrogen cycle

23.04.2018 | Earth Sciences

Joining metals without welding

23.04.2018 | Trade Fair News

Researchers illuminate the path to a new era of microelectronics

23.04.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>