Physicists solve quantum tunneling mystery

May 27, 2015
Professor Anatoli Kheifets' theory has ultrafast physics wrapped up. Credit: Stuart Hay, ANU

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

The new theory could lead to faster and smaller , for which is a significant factor. It will also lead to a better understanding of diverse areas such as electron microscopy, nuclear fusion and DNA mutations.

"Timescales this short have never been explored before. It's an entirely new world," said one of the international team, Professor Anatoli Kheifets, from The Australian National University (ANU).

"We have modelled the most delicate processes of nature very accurately."

At very small scales shows that particles such as electrons have wave-like properties - their exact position is not well defined. This means they can occasionally sneak through apparently impenetrable barriers, a phenomenon called quantum tunneling.

Quantum tunneling plays a role in a number of phenomena, such as in the sun, scanning tunneling microscopy, and flash memory for computers. However, the leakage of particles also limits the miniaturisation of electronic components.

Professor Kheifets and Dr. Igor Ivanov, from the ANU Research School of Physics and Engineering, are members of a team which studied ultrafast experiments at the attosecond scale (10-18 seconds), a field that has developed in the last 15 years.

Until their work, a number of attosecond phenomena could not be adequately explained, such as the time delay when a photon ionised an atom.

"At that timescale the time an electron takes to quantum tunnel out of an atom was thought to be significant. But the mathematics says the time during tunneling is imaginary - a complex number - which we realised meant it must be an instantaneous process," said Professor Kheifets.

"A very interesting paradox arises, because electron velocity during tunneling may become greater than the speed of light. However, this does not contradict the special theory of relativity, as the tunneling velocity is also imaginary" said Dr Ivanov, who recently took up a position at the Center for Relativistic Laser Science in Korea.

The team's calculations, which were made using the Raijin supercomputer, revealed that the delay in photoionisation originates not from quantum tunneling but from the electric field of the nucleus attracting the escaping electron.

The results give an accurate calibration for future attosecond-scale research, said Professor Kheifets.

"It's a good reference point for future experiments, such as studying proteins unfolding, or speeding up electrons in microchips," he said.

Explore further: Research team devises a means for measuring quantum tunneling time

More information: Interpreting attoclock measurements of tunnelling times, Nature Physics (2015) DOI: 10.1038/nphys3340

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richardwenzel987
2 / 5 (5) May 27, 2015
It seems that all this quantum strangeness is telling us that, at the most fundamental level, reality is not at all obedient to Aristotle. Principles like "A is A" are only emergent and only statistical in nature. If a fellow wanted to waste time being philosophical, you could get a lot of mileage out of such speculations, I think. Could be the basis for an academic career.
RichManJoe
1.5 / 5 (2) May 27, 2015
Please define instantaneous time and imaginary velocity. Ionization is not imaginary. This means that the electron left the atom during the ionization process, implying there is a distance between the (now ionized) atom and its former electron. Since distance = velocity * time, with velocity being imaginary and time being instantaneous, how does distance reconstitute to reality? When one is speaking of imaginary velocity, are they referring to SQRT(-1)*v, or are they talking about some other form of imaginary-ness? Also, over what distance can instantaneous time and imaginary velocity be caused to function?
Mark Thomas
1.4 / 5 (7) May 27, 2015
"quantum tunneling is an instantaneous process"

The tunneling electron has mass but it is effectively traveling faster than the speed of light across a barrier. I wonder what Einstein would say?
SoylentGrin
5 / 5 (6) May 27, 2015
The tunneling electron has mass but it is effectively traveling faster than the speed of light across a barrier. I wonder what Einstein would say?


It isn't travelling. At no point was the electron in the space between the points. It ceased to exist on one side, and began to exist on the other. No movement across the points at any velocity, superluminal or otherwise.
antigoracle
4 / 5 (4) May 27, 2015
"quantum tunneling is an instantaneous process"

The tunneling electron has mass but it is effectively traveling faster than the speed of light across a barrier. I wonder what Einstein would say?

Spooky behaviour close by.
Mark Thomas
2.6 / 5 (11) May 27, 2015
"It isn't travelling."

Ok, but that is putting a pretty fine point on the term "traveling" because the net effect is the same. Exactly how many ways can one get from point A to point B without traveling? Apparently the answer is "at least one, possibly more."

So we will never be able to "travel" to Alpha Centauri in less than 4.3 years, but can we get there faster by tunneling, warping, wormholing, etc.? This makes exceeding the speed of light seem more like a game of semantics than an actual barrier.
SoylentGrin
4.8 / 5 (4) May 27, 2015
So we will never be able to "travel" to Alpha Centauri in less than 4.3 years, but can we get there faster by tunneling, warping, wormholing, etc.?


Yep. Nothing can traverse spaces at speeds exceeding the speed of light. However, if you can reduce the amount of space between two points (wormholes) or can simply stop existing at one point and start existing at another (tunneling) you can get from one point to another in less time than traversing the distance. It doesn't remove the limitations on traversing the whole distance, though. The speed of light is still the speed of light.
Eikka
3 / 5 (2) May 27, 2015
Exactly how many ways can one get from point A to point B without traveling?


The particle doesn't "go" from A to B, it exists at both A and B, or neither, until it is measured to be in either or.

The probability wave is what travels between the measuring points A B, but that propagation happens at the speed of light before the tunneling actually takes place. The wave spreads out in space-time, reflects, interferes, leaks behind barriers, and then finally interacts with something and collapses into the particle.

The particle may appear anywhere the wave has spread to, and it appears instantly. The thought that it "goes" from somewhere to somewhere is simply because we erroneously assume that it must be somewhere and then teleport from there to the place where it shouldn't be.
Eikka
3 / 5 (2) May 27, 2015
Quantum tunneling is illustrated as like shouting at a wall.

You yell "HUP" really loud and you hear the echo of your own voice bounce back, but another person on the other side of the wall hears a muffled "hup" as well. This is like the propagation of the probability wave of a particle. It goes to both places.

In quantum mechanics though, the particle IS the probability wave and it can appear as a particle in a single place only. So if your shout was an electron, it would sometimes bounce back at you, and sometimes it goes through the wall to the other guy. Only, like the echo of the sound, you don't see it coming until it actually hits you - or not if the other guy got it.

Eikka
4.2 / 5 (5) May 27, 2015
but can we get there faster by tunneling, warping, wormholing, etc.?


If you could find a barrier, the other side of which was at Alpha Centauri, then you could throw people at the barrier really really hard and some might tunnel to the other side.

The rest would just go splat.

PhysicsMatter
5 / 5 (3) May 27, 2015
May be we solved QT mathematically and engineer it but we are far from understanding it.
Unfortunately, experimental results are "mis"interpreted "in layman terms" in popular science publications and only confuse rather than clarify issues by invoking weird elements in play for scientific advertisement and perhaps recruitment of young to "exiting" scientific fields. You hear much more humility, doubt and see acute awareness of speculative aspects of QM observables when these issues are discussed on professional seminars and are enclosed in mathematical symbolism that does not need nor have analogy to concepts of everyday life.
An interesting take on those misconceptions about QM as describing reality I found at:
https://questforn...-quanta/
Discussion about TR weirdness as commonly perceived I found at:
https://questforn...ativity/
And interesting reading about general problem of experimental interpretation of theories:
https://questforn...reality/
Mark Thomas
1.3 / 5 (6) May 27, 2015
The tunneling particle does go someplace. Consider a Zener diode in reverse voltage breakdown mode. Electrons would not flow through the device without quantum tunneling. A Zener diode costs less than a dollar, but it has value because it transports electrons under certain conditions that are useful in some circuitry. So from an overall perspective, quantum tunneling allows electrons to enter one side of the Zener diode at point A and exit the other side at point B.

This isn't limited to photons and electrons either. If a proton weren't able to tunnel across the Coulomb barrier of another proton, then fusion at the core of the sun and smaller stars would fail. So from our perspective, we should be thankful that proton was able to go from point A outside the barrier to point B inside the barrier and release energy.

Mark Thomas
1.5 / 5 (6) May 27, 2015
PhysicsMatter, some of us are having difficulty following your links.

met a more fishes
4.7 / 5 (3) May 27, 2015
liking these comments, i tend to think of it as two points in space being the same point in space for some quantum information, allows for workaround of speed of light. related to non-locality.
tmarksur
1 / 5 (2) May 27, 2015
"It isn't travelling."

Ok, but that is putting a pretty fine point on the term "traveling" because the net effect is the same. Exactly how many ways can one get from point A to point B without traveling? Apparently the answer is "at least one, possibly more."

So we will never be able to "travel" to Alpha Centauri in less than 4.3 years, but can we get there faster by tunneling, warping, wormholing, etc.? This makes exceeding the speed of light seem more like a game of semantics than an actual barrier.


It will depend on the energies needed to enable these things though.

Is your name mark thomas? we seem to share the same (very rare) name.
Mark Thomas
1 / 5 (5) May 27, 2015
Two Mark Thomases on the same comment thread, doesn't that double the chances of a Mark Thomas being correct? The world is in trouble now. :-)
dedereu
not rated yet May 27, 2015
Well known since the beginning in the equations of quantum mechanic and thus nothing new solved.
Radioactivity is tunneling and desintegration of Uranium atoms with a half time around a billion years is not an instantaneous process !! but a very few number of U atoms can desintegrate in less than a microsecond at random over a billion years, this is what they call an instantaneous process, the beginning of tunneling, or the time taken by the quantum wavefunction to pass trough the barrier inside the nucleus, which is not the measured random time !!
ichisan
2.3 / 5 (3) May 27, 2015
Once we abandon our obsolete assumptions and realize that distance is an illusion and that there is no time dimension, then it all starts to make sense. Nonspatiality and nontemporality are not new ideas.
adam_russell_9615
1 / 5 (1) May 27, 2015
If a mass has an imaginary velocity then does it have negative energy?
ke=mv^2
big_hairy_jimbo
5 / 5 (1) May 28, 2015
Right so line up a a shiteload of barriers interspaced accordingly all the way to Alpha Centauri, and all aboard the Quantum tunneling Star ship!!! Now if only those barriers would stay put!!!!

I seem to recall this kind of thing being done years ago, with many barriers all lined up to achieve super luminal velocities. The more barriers the faster light "seemed" to travel through vs the same distance in a vacuum. I also recall someone played classical music through this system to prove that a signal COULD be sent this way.
Anyway, no doubt someone will correct me, so I look forward to the evidence based denials.
MaxwellsDemon
1.6 / 5 (7) May 28, 2015
"Imaginary time?" 0.o Who ordered that?

Some excellent comments in this thread, thanks! If anyone can explain the meaning of imaginary time that would be great - are we looking at a second axis of time in a complex plane here or what? My inner Spock has only this to offer: "Fascinating."
antialias_physorg
5 / 5 (5) May 28, 2015
seem to recall this kind of thing being done years ago, with many barriers all lined up to achieve super luminal velocities. The more barriers the faster light "seemed" to travel through vs the same distance in a vacuum. I also recall someone played classical music through this system to prove that a signal COULD be sent this way.

Nothing travveled fatser than light in their experiments (They did show that you can have a group velocity faster than light - but that does not mean anything in the group - least of all information - travelled faster than light)

As for the 'lots of barriers': The problem is that you aren't guaranteed that something will tunnel. The larger the barrier/the more barriers the lower the probability.
marko
1 / 5 (1) May 28, 2015
Can someone please explain how in complex numbers the real number component can have a consistent dimensionality as the imaginary component.

It seems the complex component of an imaginary number must have a dimensionality of 0.5 of the real component, because multiplying two pure imaginary numbers gives a real number.

Its like saying two half apples equals an orange.

This is a complex situation to unravel.
Mark Thomas
2 / 5 (8) May 28, 2015
"Anyway, no doubt someone will correct me, so I look forward to the evidence based denials."

Jimbo, I feel the same way. The physicists in the article above concluded QT is instantaneous. What the article didn't say is that some people have at least suspected this to be true for decades. Yet when other people think a result is challenging special relativity they leap in to its defense. Oh no, they say, that particle isn't really travelling, it just reappeared in a different location when its probability function collapsed, or it was always there or some such thing.

That is a distinction without a difference. A particle approached a barrier it had insufficient energy to cross, then instantaneously passed to the other side of the barrier, some real distance away. If you don't like that conclusion, take it up with the physicists listed above, but don't be surprised that they got it right.
Thnder
1 / 5 (5) May 28, 2015
The problem is that you aren't guaranteed that something will tunnel.

Unless I am mistaken, the chances that something will tunnel can now be improved.

With this new protocol, the researchers have experimentally achieved 88 percent transmission fidelity, twice the classical upper limit of 44 percent.

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

TimLong2001
3 / 5 (2) May 28, 2015
My instructor for Laser Systems Design (a LANL physicist) at the UNM Los Alamos Graduate Center, said the you can think of a 90 degree rotation into the complex plane as like a 180 degree rotation in the real world. An idea that neatly corresponds with the binary dipole photon structure representation.
Captain Stumpy
5 / 5 (5) May 28, 2015
but can we get there faster by tunneling, warping, wormholing, etc.?


If you could find a barrier, the other side of which was at Alpha Centauri, then you could throw people at the barrier really really hard and some might tunnel to the other side.

The rest would just go splat.

ROTFLMFAO
i really, really enjoyed this description, Eikka
THANKS
Koen
1 / 5 (1) May 29, 2015
If lots of electrons more or less tunnel simultaneously, is that equivalent to a violation of local charge conservation d(rho)/dt + div(J) = 0, where rho is charge density and J is current density, div is divergence ?? If yes, is the Josephson junction super-current actually a current?
Jayded
2.3 / 5 (3) May 31, 2015
I think that Eikka described the probability wave concept very well, the only part that sort of bothers me is that it seems like a bit a of a crutch. There are two problems with it, the first is that they allow properties of the probability wave to somehow stay within the light barrier by applying space-time warping which as far as I know is completely immeasurable and to me seems like a patch to retain the "nothing faster than light speed" scenario. It also introduces another problem, the concept of "instantaneous", this process as I understand it happens in measurable time, it exists, doesnt, then does or rather, it exists and then it exists on either side of a barrier without travelling through the distance in the middle. I just cant see this happening. Even on the sort of time scales involved and object should go through processes of non existence and then on the other side go through processes of existing. If you will look at it as an object what part of it stops existing first?
mytwocts
1 / 5 (1) May 31, 2015
In quantum mechanics nothing travels faster than light.
mytwocts
not rated yet May 31, 2015
For the actual article see http://arxiv.org/...620.pdf.
adam_russell_9615
1 / 5 (2) May 31, 2015
If a mass has an imaginary velocity then does it have negative energy?
ke=mv^2


Actually, I think another solution would be if it was a negative mass.

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