
Superconductivity Theory Under Attack - dnetesn
https://phys.org/news/2019-11-superconductivity-theory.html
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eigenspace
One of my great surprises coming into my masters degree in condensed matter
theory working with superconductors was just how poorly we understand them.

We have these incredibly seductive theoretical frameworks for thinking about
superconductors which we know are deeply flawed, but it seems nobody (myself
included) has the vision to see an alternate way of looking at them.

The tyranny of the BCS theory of superconductors is real.

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etaioinshrdlu
Do you think it's likely that the Standard Model cannot sufficiently explain
superconductivity? Or alternatively, that it can be perfectly explained, but
the actual analysis is just super difficult?

I find this interesting because pretty much everything else in day to day life
seems to have been explained by the standard model minus gravity.

~~~
eigenspace
I would be extremely surprised if we needed anything beyond non-relativistic
quantum mechanics coupled to classical electrodynamics to describe the next
theory of superconductivity. If there is anything beyond that required, I
would be absolutely stunned if it was more advanced than relativistic quantum
electrodynamics.

The trouble with condensed matter physics has never been that the underlying
phenomena are complicated. We’ve had a more sufficient grasp of the
microscopic physics of materials since the 40s. I could write down the
complete ‘theory of everything’ Hamiltonian for a condensed matter system in
like two lines. The trouble, is not the fundamental building blocks, but how
you take a mathematical description of electrons bumping into ions and then
generalize that to 10^23 electrons and ions.

The game is to make an approximation that gets rid of the stunning complexity
of the full theory without while still preserving the features that are
relevant to the problem you’re trying to solve.

Imagine trying to understand how a modern computer running a video game works,
but all you understand is the basics of logic gates. Sure, in principal you
could understand what’s going on in terms of bit flips, but it’s hopeless in
practice. Interacting, strongly correlated quantum mechanical systems are very
literally _exponentially_ more complex than a classical system like a
computer.

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mrob
>Imagine trying to understand how a modern computer running a video game
works, but all you understand is the basics of logic gates. Sure, in principal
you could understand what’s going on in terms of bit flips, but it’s hopeless
in practice.

See "Could a Neuroscientist Understand a Microprocessor?":

[https://journals.plos.org/ploscompbiol/article?id=10.1371/jo...](https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1005268)

(which is actually looking at transistor-level data, not gate-level, but the
games examined are simple ones)

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eigenspace
Yes, I was thinking of that article when I wrote the above comment. Thanks for
the link!

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jl2718
I really wish physics articles would talk about the actual measurements. It
sounds like they are using shrunken gnomes to observe electrons. Is it
spectroscopy? Simulation? I think the truth would be a lot less exciting than
what the article claims, but if you’re going to lie, might as well just write
science fiction. Science journalism has never been great, but now it’s
intentionally misleading.

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FreeFull
The article says they use UV photons to kick electrons off the surface, and
then measure the trajectories of the electrons

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sfink
Interesting to see this alongside "Physicists Have Identified a Metal That
Conducts Electricity But Not Heat" which is talking about another material
where electrons exhibit collective behavior, "moving as a fluid". Perhaps
there are a number of situations where electrons coordinate within a metallic
lattice, but something additional is required to produce superconductivity.
Cooper pairs could be degenerate (or at least very simple) forms of this
collective behavior.

Or maybe vanadium oxide _is_ a room temperature superconductor, it's just that
any amount of current destroys the effect unless it's really cold, cold enough
for everything to stay put.

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dspillett
> ... at 4.2 Kelvin (4.5 degrees above absolute zero, ...)

Is my understanding wrong (or out of date) or the article bad at this point?

I thought the Kelvin scale was designed such that its base _is_ absolute zero
so 4.2 Kelvin would be 4.2 degrees above not 4.5?

EDIT: Actually, looking at the num-pad on my keyboard, I'm now assuming that
the "4.5" is simply a slip-of-the-finger typo rather than a mistake in
understanding.

~~~
lgats
also,

4.2 K = -452.11 F = -268.95 C

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travisoneill1
Why would you need a quantum computer to simulate behavior that has to do with
quantum mechanics?

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tempsolution
Probably two things. On one hand, our theoretical understanding of quantum
effects may not have come far enough to write a traditional simulation
program. Or doing so would take years or even millions of years, or both.

Quantum computers can simulate things that are not possible with traditional
computers. These problems are in the complexity class BQP. I want to point out
though, that this is very likely a result of our limited understanding, and
not something that is theoretically impossible.

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fooker
How do you know the quantum simulation will match the actual phenomenon. There
seems to be a leap of logic there.

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pixl97
How do we know that classical numerical simulation will match the phenomena...
by experimentation.

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fooker
Experimentation in the quantum world has this nasty habit of changing what you
are trying to observe.

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spectramax
Why use a strong violent word - "Attack"? This kind of journalism bothers me.
"New research questions Superconductivity Theory" should be sufficient.
"Attack" is a poor word choice IMHO.

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pera
"attacking" a theory is a very common expression used in many scientific
literature.

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sgt101
So what scale of QC would be needed to do this work?

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asdfasdfdavid
This looks like it could be a huge turning point for the understanding of
matter at temperatures we love.

