How long does it take an electron to tunnel?

How long does it take an electron to tunnel?
Ionization times (left axis) reconstructed using the ARM theory from offset angles (right axis) obtained numerically using TDSE calculations. Red circles are the numerically calculated offset angles, divided by the laser frequency, θ/ω. Blue diamonds show the offset angles with the correction due to the substraction of the pulse envelope effect, ti0 = θ/ω-|Δtienv (θ,ppeak)| . Green inverted triangles show the Coulomb correction to the ionization time evaluated at the peak of the photoelectron distribution, |ΔtiC (θ,ppeak|. Orange triangles show the ionization times we obtain by applying the reconstruction procedure defined by equation (4) in the paper. In terms of the figure, this is simply the result of subtracting the green curve from the blue curve. Credit: MBI

The combination of ab-initio numerical experiments and theory shows that optical tunnelling of an electron from an atom can occur instantaneously.

How long does it take an atom to absorb a photon and lose an electron? And what if not one but many photons are needed for ionization? How much time would absorption of many photons take? These questions lie at the core of attosecond spectroscopy, which aims to resolve electronic motion at its natural time scale.

Ionization in strong infrared fields is often viewed as electron tunnelling through a potential barrier, created by the combination of the atomic potential that binds the electron and the electric field of the laser pulse that pulls the electron away. Thus, unexpectedly, attosecond spectroscopy finds itself facing an almost age-old and controversial question: how long does it take an electron to tunnel through a barrier?

In the paper by Torlina et al, this question is studied by using the so-called atto-clock setup. The attoclock uses the rotating electric field of a circularly polarized laser pulse as a hand of the clock. One full revolution of this hand takes one laser cycle, about 2.6 fs for experiments with 800 nm pulse of a Ti-sapph laser. As the electric field rotates, so does the tunnelling barrier. Thus, electrons tunnelling at different times will tunnel in different directions. This link between time and direction of is what allows the attoclock to measure times. In every clock, a time zero must be established. In the attoclock, this is done by using a very short laser pulse, which lasts only one-two cycles. Tunnelling occurs in a small window where the rotating passes through its maximum.

Next, like any other clock, the attoclock must be calibrated. This calibration of the attoclock has now been accomplished by Torlina et al, with no ad-hoc assumptions about the nature of the ionization process or the underlying physical picture.

Combining analytical theory with accurate numerical experiments, and having calibrated the attoclock, the authors could finally carefully look at delays in electron tunnelling. They arrive to the surprising answer: this time delay may be equal to zero. At least within the realm of non-relativistic quantum mechanics, the electron tunnelling out of the ground state of a Hydrogen atom spends zero time under the tunnelling barrier. The situation may change, however, if this electron encounters other electrons on the way, which may become important in other atoms or molecules. The interaction between the electrons may lead to delays.

Thus, the attoclock provides a unique window not only into the tunnelling dynamics, but also into the interplay of different electrons that participate in the ionization process, and how the electrons staying behind readjust to the loss of their comrade.


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More information: "Interpreting attoclock measurements of tunnelling times." Nature Physics 11, 503–508 (2015) DOI: 10.1038/nphys3340
Journal information: Nature Physics

Citation: How long does it take an electron to tunnel? (2015, August 25) retrieved 25 June 2019 from https://phys.org/news/2015-08-electron-tunnel.html
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Aug 25, 2015
Time is relative. Effectively it does not exist in some cases.
What is it? Perhaps a misconception. Truth and reality have not a lot to do with subjective perception. It is so much fun! This article is fascinating. Nature is the Mother.

Aug 25, 2015
for those interested, you can find the pre-print version here (arXive- free):
http://arxiv.org/abs/1402.5620

http://arxiv.org/...20v2.pdf

Aug 25, 2015
how do they know that it is the same electron going in and coming out?

Aug 25, 2015
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Aug 25, 2015
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Aug 25, 2015
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Aug 25, 2015
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Aug 25, 2015
docile- matter cannot travel through space at faster than the speed of light.
waves in 'space' (the quantum background) have no such limitations. space traveling has no such limitation. Space expanding has no such limitations. There are plenty of mechanisms. and plenty of misunderstanding.

Aug 26, 2015
This is another misinterpretation by phys.org of the major point of the paper. These are not tunneling times (time it takes to tunnel) authors are talking about but the times associated with rotating EM wave (laser) electric field encountering an electron on its path and they simply suggesting or vaguely infer that such a effect could be associated with tunneling under big assumption that at those times electron encounters the E-field barriers and "passes" it.

Aug 26, 2015
If fact tunneling as described by QM is instantaneous since, while a wave function in Dirac equation can depend on time, the probability density ( in this case probability of the electron existing beyond the barrier interpreted as crossing it) derived from the wave function is stationary time-independent so there could be no tunneling times since it is instantaneous) and hence in this case it suffice to solve Schrodinger equation and not Dirac equation to address the issue of tunneling.

More misconceptions or misinterpretation about the reality of difficult to understand quantum tunneling and other aspects of QM can be found at:

https://questforn...-quanta/

Aug 26, 2015
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Aug 26, 2015
Some of us have known about instantaneous QM tunneling for a long time. If it weren't instantaneous, nearby particles could move into both the starting and ending positions for the tunneling particle while it was tunneling, giving rise to a bit of a problem. In that case we would need a separate mechanism to prevent the tunneling particle and a nearby particle from being in the same place at the same time.

Aug 26, 2015
Some of us have known about instantaneous QM tunneling for a long time.

And you published this 'insight' exactly...where?

Sorry...but posting in hindsight that "you knew it all along" is disingenuous (and pretty pathetic).

Aug 27, 2015
Antialias, my point is simply that if more people had kept an open mind about this, they would have at least suspected that QM tunneling is instantaneous decades ago. Perhaps it was the fear of contradicting Einstein that has held us back in this area. Instead of getting all bent out of shape that something had an "apparent" velocity greater than c, we should have realized the tunneling particle is not traveling in normal space-time, so Einstein's relativity is still intact.

Here's a paper from 1998 that refers to instantaneous QM tunneling: http://arxiv.org/...9053.pdf

This would not be the first time that science had a bias that slowed progress. For example, for a long time the existence of bacteria underground was thought to be impossible. Detection of bacteria on drill bits was considered to be contamination from the surface. This held back the field of astrobiology for years.

Aug 27, 2015
Antialias, you obviously misinterpreted my comment, but I argued QM tunneling is instantaneous on this very website three months ago.

http://phys.org/n...ery.html

The first sentence of that article reads, "An international team of scientists studying ultrafast physics have solved a mystery of quantum mechanics, and found that quantum tunneling is an instantaneous process."

Aug 27, 2015
Gee, this is so complicated: How long is "instantaneous". is it zero time ? In which case tunneling is faster than the speed of light !! I am not sure you can "tunnel" thru space if space isn't anything. Very complicated. Maybe it's the author.

Aug 28, 2015
Anti_alias, you should do a basic google search when you are ignorant of the facts, as you were in this case. Over two decades ago, in 1994, the following book concluded for "photonic tunneling experiments" that, "[t]he evanescent region has shown to be a mysterious medium, where group, energy and according to the Sommerfeld and Brillouin definition signal velocities can exceed the vacuum velocity of light."

Advances in Quantum Phenomena, Page 199, edited by Enrico G. Beltrametti, Jean-Marc Lévy-Leblond

https://books.goo...;f=false


Aug 28, 2015
Antialias, my point is simply that if more people had kept an open mind about this, they would have at least suspected that QM tunneling is instantaneous decades ago


No. You said you 'knew' this. Not that you suspected (from theory). That there is a theory that says it's instantaneous isn't news to anyone.
However, there's a real difference between having a theory and actually doing an experiment.

(and the book-source you cite is about something entirely different. That is concerned with group velocities)

Aug 28, 2015
"No. You said you 'knew' this. Not that you suspected (from theory)."

Give me a break anti_alias, you are not considering the many published experiments. What level of proof do I need to write, "Some of us have known about instantaneous QM tunneling for a long time." You are attempting to cover up your ignorance of this topic with semantic games and by ignoring everything else I wrote. The book I cited, and quoted with a link, is clearly on point. I wrote about this 3 months ago on this very website and provided the link. The bottom line is others (not me) have written in publications for years that instantaneous QM tunneling is the most likely explanation, yet many people (such as you?) dismissed it out of hand without giving it the consideration it deserved. Those people were wrong, wrong, wrong. Whether you like the science or not, these are the results the researchers have published for years, not me ok?, so take it up with them if you don't like it.

Aug 28, 2015
Willful ignorance of scientific results will never help us move forward.

Aug 31, 2015
If you bother to read the grafts explanations, they made a whole bunch of mathematical assumptions to come up with the grafts. If the assumptions are correct than all is well otherwise it is garbage in garbage out.

Aug 31, 2015
Time is relative. Effectively it does not exist in some cases.


Never in reality.

Without time no observable thing exists. Without things no observable time exists.


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