
Superconductivity offers tantalising changes from electricity to transport - jonbaer
https://www.ft.com/content/08c4109c-d8f1-11e7-9504-59efdb70e12f
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pyedpiper
This article is kind of whack... Yes modern superconducting materials are
getting warmer and warmer. No we're not at room temp now. No there's not a
clear path to simulating band gaps for extended structure materials with the
quantum computing..

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selimthegrim
No, but if you could make Variational Quantum Monte Carlo work better by
starting with a good variational guess in your quantum simulator....

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imglorp
What would room temperature superconductivity actually buy society? I can
think of a few things but I'm not sure about the implications.

* Long distance transmission is currently high voltage AC to work around losses. The whole distribution network would become efficient but would need reinvestment. This would offset the utility of local instant-response power generation.

* Things that need big magnets would get easier: MRI, particle accelerators, etc. Is this a big deal? Maglev trains would get more attractive.

* What else?

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XorNot
Low voltage distribution networks in data centers. Forget 48v - you could
centrally distribute 3.3v power for CPUs. 1000s of 80% step down converters
become 100% efficient.

Superconducting ring storage of electricity.

Probably some break throughs in electrical storage because SQUID devices can
now be commodity parts in hard disks.

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Dylan16807
> Low voltage distribution networks in data centers.

3.3v (or lower, for modern chips) requires _big_ cables. I doubt that's worth
it.

> 1000s of 80% step down converters become 100% efficient.

How does this happen? Are you excluding the efficiency of the central step-
down converter?

> Superconducting ring storage of electricity.

Can you actually fit a meaningful amount of energy in there before it
saturates?

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Robotbeat
Big cables not needed as superconductors can carry more current per unit cross
sectional area than copper.

Even one central step-down converter could be 98% (or whatever) efficient,
plus you could actually generate power at 3.3V if you wanted to, making step-
down not required.

As far as storage of energy, yeah, you can store a lot of energy in a
superconducting ring. It is a viable energy storage method.

THAT ALL SAID, the physics of superconductivity mean that even if you ARE able
to get room temperature superconductivity to work, you can get even BETTER
critical current (i.e. current per cross section area that can be handled
while maintaining a superconducting state) so you'll still probably want to
cool the cables in some applications, and for a certain current carrying
capacity, you'll probably want to use a higher voltage than just 3.3V, even if
you don't have any voltage drop, because that would increase the power that
can be transmitted for the same cable investment.

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justinclift
Hmmm, wonder what the cascade failure of a "full" superconducting ring heated
past it's superconducting point would look like?

Maybe impressive fireworks/explosion?... from a safe distance. :D

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Robotbeat
Good question! The thing you're referring to is "quench." Answer:
[https://en.wikipedia.org/wiki/Superconducting_magnet#Magnet_...](https://en.wikipedia.org/wiki/Superconducting_magnet#Magnet_quench)

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justinclift
Thanks, that's interesting info. It's good there seems to be well established
ways to detect and cope with this. :)

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selimthegrim
Vanilla DFT is still a ground-state theory, last time I checked, which means
it can't tell you the things about the Fermi surfaces you would most like to
know for superconductors. I can't speak for quantum simulation.

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baybal2
I wonder, if cooper pairs can be made with ions?

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marcosdumay
As a rule, the heavier your particles, the harder it is to get quantum
mechanics behavior out of them. You won't see atoms forming Bose-Einstein
condensates at anything you can cool with liquid nitrogen.

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neonate
[http://archive.is/gE8kw](http://archive.is/gE8kw)

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deepnotderp
Haven't carbon nanotubes already been shown to exhibit ballistic conduction at
room temperature?

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Robotbeat
Ballistic conduction is not the same as superconductivity.

Superconductivity relies on Cooper pairing, i.e. charge carriers that are
(relatively weakly) bonded together such that the even smaller interactions
with imperfections (including just thermal dislocations) in the conducting
medium are even smaller than the minimum energy needed to break the Cooper
bond. Until this minimum energy is achieved, then the Cooper pair is quantum
mechanically prohibited from losing energy (to resistance/heat) from these
small imperfections, similar to how an electron is quantum mechanically
prohibited from swirling into the nucleus (losing energy in the form of
electromagnetic radiation due to traveling in a circle, i.e. accelerated, as
classically one would expect) from the ground state.

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deepnotderp
I know the differences between the two, perhaps I should've elaborated more.
My point was that other than the Meissner effect, from a practical standpoint
ballistic conduction is just as useful in terms of electron mobility.

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Robotbeat
Ballistic conduction does raise the possibility that the bulk electrical
resistivity of carbon nanotubes or graphene (etc) could be lower than (say)
copper, but this is not practically as useful as superconductivity. The
Josephson Junction (which is at the heart of SQUIDS--used for measuring
extremely small magnetic fields--and also superconducting qubits--probably the
most promising of the current quantum computing technologies) relies on the
quantum mechanical nature of the phenomenon.

Because of Cooper pairing, you can avoid resistance even at the interface
between one superconductor and another, thus allowing the complete cessation
of all resistance. This allows you to store energy in the form of continual
circulating current with no energy input, something that wouldn't be practical
with merely much lower electrical resistance enabled by ballistic conduction
(which still has significant tube-to-tube resistivity).

So I'd say that probably most practical applications of superconductivity are
not transferable to ballistic conduction. Still nice to beat copper in
conductivity (which hasn't happened with carbon nanotubes and graphene except
for microscopic samples or with corner cases like high temperatures, high
frequencies, etc).

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deepnotderp
Fair enough, I wasn't thinking about the quantum computing side :)

