# Physicists watch quantum particles tunnel through solid barriers. Here's what they found.

#### tommytoes

Trying to wrap my head around the math here and was hoping someone could help me out.

moving them about 0.15 inches per second (4 millimeters/s)
barrier was 1.3 micrometers (microns) thick
it took them about 0.6 milliseconds to traverse the barrier

Was there a rate of acceleration or deceleration here upon encountering the barrier? It seems slow versus the initial observations that it's instant or near instant.

#### David F Walter

Trying to wrap my head around the math here and was hoping someone could help me out.

moving them about 0.15 inches per second (4 millimeters/s)
barrier was 1.3 micrometers (microns) thick
it took them about 0.6 milliseconds to traverse the barrier

Was there a rate of acceleration or deceleration here upon encountering the barrier? It seems slow versus the initial observations that it's instant or near instant.
RESPONSE:
At a velocity of 4 mm/sec, the rubidium atom would need 0.33 msec to traverse 1.3 microns. This is 1.3 * 10^-6 / 4*10^-3 seconds. With the observed time of 0.6 msec to cross the barrier, the implication is that the barrier induced a 0.27 msec delay.

It would be interesting to know the exit velocity from the barrier. This might indicate whether the tunneling changed the momentum of the particle reversibly or irreversibly inside the barrier. Or otherwise stated, does the particle return to its original entrance velocity or not as it exits the barrier.

David F Walter

#### EMN

I believe David's calculations are correct. However there is a round-off error in the article.

.15 inch/sec = 3.81 mm/sec. This means it lost a little less speed , but it still lost some.

David's question is what I am curious about as well. What was the speed after it exited and what direction was it in compared to the initial direction.

-Eric

tommytoes

#### SteveMDFP

"The barrier induced a 0.27 msec delay."
Where *exactly* was the atom during that 0.27 msec? I'm guessing it was in superposition, on both sides of the barrier simultaneously.

#### cashme

A team of physicists has devised a simple way to measure the of a bizarre phenomenon called quantum tunneling.

Physicists watch quantum particles tunnel through solid barriers. Here's what they found. : Read more
"Fundamental particles such as an electron are real, extended particles each of size equal to its De Broglie wavelength, rather than a point-particle-probability-wave. Potential energy is gained as the particle traverses the barrier that is cleared; even though its initial kinetic energy was less than the barrier height. Energy conservation is obeyed at all times. Tunnelling arises from physical laws.":
This understanding was known since 1990, by derivations realized without any assumptions of waves, without the use of any of the 41 free parameters or postulates that are required to try and make quantum mechanics work. The first principles are :

The first principles used were:
1 ) Haus re-derivation of Goedecke’s non radiation condition in a new way(1986 at MIT):
Haus, H. A. (1986). "On the radiation from point charges". American Journal of Physics. 54 (12): 1126–1129. Bibcode:1986AmJPh..54.1126H
2 ) Maxwell’s/Heavysides’s electro-magnetic formulas
3 ) Einstein’s Special Theory of Relativity
4 ) The Stern-Gerlach Experiment
5 ) The DeBroglie Matter-Wave formulations

These first principles were first used in 1986, by Herman Haus, Institute professor of electronic engineering at MIT, to answer the question, "What is the quantum level mechanism at work in the Free Electron Laser?" This was asked by the USA Department of Defence. The answer, derived by Haus, was a purely classical mechanism and which answer was accepted by the DoD in 1986 and then by the academic physics community in 2019. Using those same first principles, Randell Mills with the help of Hermann Haus, started the derivation of the Grand Unified Theory-Classical Physics (GUT-CP) and later with the help of John J. Farrell, a Chemistry professor at Franklin and Marshall College, published in 1990, the fuller thesis of this theory.
By using GUT-CP as a guide to guide their development, at least four items were developed. Since not one items has been successfully developed using accepted Standard Quantum Mechanics then, the case for GUT-CP is much greater than that for SQM.

Do consider this in a serious way, and do not just try to ban me from this site. There are many others who will continue to spread the word.

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Very cool (literary) experiment! While simple in principle and complicated in practice, they can tease apart the effects both experimentally and theoretically. The measurement is weak, so they have to integrate out the result - the ground state of the tunneling require simulation over an imaginary time axis - and they get that "about 40% of the measured time for the lowest incident energy comes from the time spent in the classically forbidden region."

And of course there is the traversal time estimate: "At the lowest incident velocity (4.1 mm s^−1), we observe a transmission probability of 3%. Given the energy dependence of the transmission, we calculate that the transmitted atoms have a velocity distribution with a peak at 4.8 mm s^−1, corresponding to κd ≈ 3. About three-quarters of this distribution cor-responds to energies below the barrier height. The measured traversal time τ_y is 0.61(7) ms."

It would be interesting to know the exit velocity from the barrier. This might indicate whether the tunneling changed the momentum of the particle reversibly or irreversibly inside the barrier. Or otherwise stated, does the particle return to its original entrance velocity or not as it exits the barrier.

Unfortunately the measurement is complicated and the particle behavior also depends on a measurement backaction.

"Considering incident particles polarized in the x direction and a magnetic field along z, one would expect the spin to precess by an angle θ = ω_Lτ, where ω_L is the Larmor frequency and τ is the time spent in the barrier. By working in the limit of a weak magnetic field (ω_L →0), this time can be measured without substantially perturbing the tunnelling [sic] particle. Büttiker15 noted that even in this limit, measurement backaction cannot be neglected, and it results in preferential transmission of atoms aligned with the magnetic field. This leads to two spin rotation angles: a precession in the plane orthogonal to the applied magnetic field, θ_y, as well as an alignment along the direction of the field, θ_z. He defined times associated with the spin projections: τ_z, τ_y and τ_x=sqrt(t_y^2+t_s^2); the latter is often known as the ‘Büttiker time’. It turns out that combinations of two such quantities appear in other theoretical treatments as a single complex number33,34, but researchers were hesitant to accept complex-valued times without a clear interpretation. Later, further studies11,12 associated τ_y and τ_z with the real and imaginary parts of the ‘weak value’13 of a dwell-time operator, thereby providing them with distinct interpretations as the inherent tunnelling time and the measurement backaction, respectively."

"We investigate the two Larmor times by performing full-spin tomography of the transmitted spin-½ particles. Rotations after the scattering event enable us to measure the spin components along the x, y and z axes of the Bloch sphere (Fig. 4b). From the different projections, we find the traversal time τ_y and the time τ_z associated with the backaction of the measurement (Fig. 4c). At the lowest incident velocity (4.1 mm s^−1), we observe a transmission probability of 3%. Given the energy dependence of the transmission, we calculate that the transmitted atoms have a velocity distribution with a peak at 4.8 mm s^−1, corresponding to κd ≈ 3. About three-quarters of this distribution corresponds to energies below the barrier height. The measured traversal time τy is 0.61(7) ms."

"The total duration of the simulations is set such that all the atoms have finished interacting with the barrier. By setting the scattering lengths to zero, we go from the Gross–Pitaevskii equation, also known as the nonlinear Schrödinger equation, to the Schrödinger equation. We find no major differences between the interacting and the non-interacting cases (see Extended Data Fig. 2)."

The passing of the barrier is a complicated situation, especially in this setup.

Where *exactly* was the atom during that 0.27 msec? I'm guessing it was in superposition, on both sides of the barrier simultaneously.

Good question!

It is easier to think of the elementary particles as particles of their quantum fields at first. The field penetrates the barrier but there is no probability current inside the barrier, there is no observable particle inside the volume [ https://en.wikipedia.org/wiki/Probability_current ] but it is its wave function (describing the particle probability amplitude) that has been delocalized over the barrier [ https://en.wikipedia.org/wiki/Quantum_tunnelling ].

Pulling that back to the atom, if it tunnels as a coherent system - as we can see it does - I doubt you can say it existed - was observable - in the common sense definition during the tunneling time. Quantum fields are funny things, they answer the classical question "particle and/or wave", but not always in the way we would think.

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#### Valentine Michael Smith

If ulimately only fields exist, why do people continue to think in terms of particles, rather than self-propogating wakes?

#### cashme

If ulimately only fields exist, why do people continue to think in terms of particles, rather than self-propogating wakes?
If so then yes, why think in terms of particles. What seems to be happening in quantum physics, is that there are only a few choices, waves or fields at base of all phenomena. What if one opens those choices to include particles as consisting of waves where, the waves are very different from the kind that oscillate in terms of their charge varying across space as is commonly depicted in graphic form.

But,instead what if the particles do exist and exactly as predicted by Randell Mills' theory, the Grand Unified Theory-Classical Physics. The waves in that model consist of, resonating in place, circular standing charges of many such circles of charge combining to form a solid sphere of charge or the resulting particle. That is the kind of model that was used at MIT by Hermann Haus to answer a question posed by the USA Department of Defence , "What quantum level mechanism explains how the Free Electron Laser works?"

Besides the DoD, I also find that theory and the way particles are modelled, to work much more accurately to describe all phenomena than, when using the kind of waves used under accepted QM. for explaining phenomena.

Those statement may be taken as, being very heretical by, very many who do physics at the quantum level. The waves, as currently depicted, provide a substantial substrate that seems to work very accurately by which, very many phenomena can be explained. The reason most would find a different model of waves or field /cum waves, to be a difficult concept to entertain is, because nearly everyone uses the current model, as a common language for representing what, is happening at the quantum level. Getting away from that, would seem to require that common language having to be relearned almost from the ground up.

I have studied GUT-CP for about 7-8 years and it seems to work much better, by a factor of at least 100 times, more accurately than, the kind of quantum mechanics that uses waves or fields. This works that much better everywhere, from quarks up to the whole of the universe, plus more. Using QM, with its types of waves, nothing was ever made to work. Under GUT-CP there are currently at least 4 items that were fully developed and do work in a way that QM has no way of explaining.

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