
The geometry of an electron determined for the first time - furcyd
https://www.unibas.ch/en/News-Events/News/Uni-Research/The-geometry-of-an-electron-determined-for-the-first-time.html
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aj7
From reading the article, I think they mean “determined” in the sense of
controlled. They changed the potential distribution in the electrodes, and the
single-electron wavefunction changed in a controlled way. The “geometry” is
presumably the spatial probability distribution, including the spin.

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HNLurker2
Yes and more they know the precise geometry (position) less they know about
momentum

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Koshkin
... except that in the given context 'geometry' does not mean position.

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ulises314
Yes it does,from the abstract of the original article: "We show that in-plane
magnetic-field-assisted spectroscopy allows extraction of the in-plane
orientation and full 3D size parameters of the quantum mechanical orbitals of
a single electron GaAs lateral quantum dot with subnanometer precision."

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Koshkin
That can hardly be interpreted as talking about 'position.' Also, it helps to
remember that 1 nanometer is about 10 atom sizes.

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ttflee
IMHO the title is a little confusing.

What could be measured was the geometry of orbitals of electrons, not that of
electrons.

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ivan_gammel
Orbital is the form of wave function in atom, but here they are talking about
free electrons confined in quantum dots.

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mnl
Well, if they're confined they're not free. I guess they mean the spatial
probability density (modulus squared of the orbital wavefunction in an atom,
you might skip the orbital label if the potential is not central, but it's the
same thing) of the electron in these artificial atoms. The title is misleading
because the "geometry" of the electron is point-like (to all effects in this
case).

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neohaven
It's free in the sense that it is not bound to an actual atom.

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mnl
Free depends on the context. These electrons are in a potential well, they're
in a bound state. Actual atoms are just an example of that. My point was that
conceptually both situations are alike, as they are bound states you get
discrete spectra (roughly speaking), if they were free particles you wouldn't.
(Maybe those levels happen to be very close, but that's a different story. In
principle the _artificial atom_ name makes sense and talking about orbitals is
not a bad analogy.)

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dr_dshiv
I thought the geometry of electron orbitals was that of spherical harmonics?
Platonically beautiful, emperically validated, etc etc.

[https://en.m.wikipedia.org/wiki/Spherical_harmonics](https://en.m.wikipedia.org/wiki/Spherical_harmonics)

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antonvs
The article is referring to confined free electrons, no nucleus and therefore
no orbitals involved.

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gmueckl
In other words: different charge distribution, different potential, diffetent
resulting wave functions.

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tomrod
This is a fascinating notion to me, and while generally I get things I have no
idea what foundation I would need to understand this. What exactly is going
on?

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piannucci
The scale of this experiment is pretty big in quantum terms, so a semi-
classical explanation is not inaccurate. The electron is behaving like water
filling a bowl. The height of the bowl floor represents how much potential
energy the electron needs to reach that point in space.

Suppose that the bowl is invisible, and detailed knowledge of its shape is of
scientific interest for one reason or another. Here, it's interesting because
they want to fine-tune their ability to spatially and electromagnetically
control individual electrons so that they can explore "spintronics".

One way to measure the shape of the bowl is to measure the shape of the
electron "fluid" filling the bowl. They've developed some technique for doing
that. I haven't read the details.

That only gives you information about the bottommost part of the bowl, where
the fluid lies. By applying voltages to the electrodes, the authors can raise
the potential energy needed for the electron to hang out at one end of the
bowl relative to the other. This effectively tips the bowl, and the electron
"fluid" re-distributes itself, allowing them to measure the shape of the bowl
at locations other than the bottom.

That's all I get from the article. You'd have to read the linked original
paper to learn more. A traditional undergraduate series in classical
mechanics, electromagnetics, waves, and quantum mechanics is very helpful, but
cutting-edge research is never communicated in the same terms that are used in
undergraduate teaching. There are going to be some jargon barriers no matter
what. Happy reading!

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riemannzeta
As other commenters have noted, the title is mildly annoying. Electrons are
structureless, one of the most beautiful facts about nature. Euclidean points
actually exist all over. And have spin. :-)

Why try to sex that up? Already sexy.

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amelius
Are you sure they are structureless, or is that just based on the accuracy by
which we can measure this?

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ianai
They’re theorized to be fundamental particles. Nothing smaller exists within
them. There’s no nuclear decay of or fusion which produces electrons. Similar
to how photons are quanta of energy.

Edit: clarified that electrons don’t decay. Of course things decay into
electrons plus other things.

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hpcjoe
Er ... there are lots of nuclear decays which produce beta particles
electrons. Neutrons have a short half-life when free of a nucleus, and decay
into a proton, electron and an electron anti-neutrino (to conserve momentum).
[1]

Electrons are posited to be fundamental, and e-e e-e<sup>+</sup> collisions
haven't, as far as I know though well outside my original field of study,
produced any data suggesting internal structure.

This doesn't mean that they don't have structure, we simply have no theory
(that I know of, but then again, I'm a former solid state guy) that predicts
structure, nor do we have sufficiently powerful colliders to get us to a point
to see such structure.

[1]
[https://en.wikipedia.org/wiki/Beta_decay#%CE%B2%E2%88%92_dec...](https://en.wikipedia.org/wiki/Beta_decay#%CE%B2%E2%88%92_decay)

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ianai
Thanks, I tried to clarify that.

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bediger4000
I found the article uninformative - nowhere in it could I find a picture of
this "geometry". The incomprehensible diagrams were nice, but only because I
collect that sort of thing.

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aurbano
Open access paper here:
[https://arxiv.org/pdf/1804.00162.pdf](https://arxiv.org/pdf/1804.00162.pdf)

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teilo
Now if only we can discover what they want. Also their favorite color would be
nice.

But aside from the poor title, this is incredible work.

