Closing in on high-temperature superconductivity | Hacker News Reader

Closing in on high-temperature superconductivity

sciencedaily.com

107 pointsjonbaer70 comments

Three groups published essentially the same results in the same issue of Science:

Greiner group: https://arxiv.org/pdf/1605.02704.pdf

Zwierlein group: https://arxiv.org/pdf/1606.04089v1.pdf

Bloch group: https://arxiv.org/pdf/1605.05661v1.pdf

Thanks for sharing. I'm pretty familiar with the area, and it was fun to see the different approaches and styles of the three groups in the papers.

Zwierlein = "we're doing solid state physics" (disclaimer: with ultracold atoms)

Bloch: optical lattices and ultracold atoms are cool. You can do anything.

Greiner: quantum gas MICROSCOPES!

There's probably a serious error in the cover image caption, or the image itself is seriously misleading. I'm quoting verbatim:

> "This composite image contains an equation in the foreground related to theory research in high-temperature superconductivity, and images in the background resulting from high-temperature superconductivity experiments. Credit: Image courtesy of Penn State University"

At least one of the images in the background is not 'resulting from high-temperature superconductivity experiments', it's just a plain rendering of the default preset of a Filter Forge filter 'Electricity': https://www.filterforge.com/filters/237.html

(I am the author of this particular filter, and the founder of Filter Forge. The 'electric' image looks a bit different on our page because we force seamless tiling to on when rendering images for the web).

It saddens me that the top comment is a technical note about the eye-catcher image, not the substance of the article.

The article doesn't have a lot of substance though. It spends a lot of time on what the goals are and buries the few snippets of what they actually did and measured. They have a physical simulator and a computational simulator? Maybe? It's a mess.

Yeah, basically. From what I can tell given some work I've done in a related field, what's happened is that they found a new way to do the math in a theoretical model some long time ago, and it revealed some cool new predictions within a certain temperature range, as well as some equivalent of high-T superconductivity at some other temperature range.

Now they went to test it, which they did by supercooling potassium atoms while using lasers to force them into one place. (Conveniently you can also use lasers for refrigeration though I'm not sure if they did.) Then they switched the lasers to describe a big 2D standing wave which the potassium atoms spread out into, forming a square grid. These are called "optical lattices"; they're difficult to work with because you don't have anything small enough to really poke at individual atoms and even if you did you'd have to deal with how the lasers are blasting your poker left and right... so, you just have to kind of throw your hands up, "I am not going to care about any of these individual atoms." However, you get some nice bulk properties: for an easy example, if you just turn off the lasers and let stuff drift and then image it, they all basically started from the same place and drifted according to their velocity which is proportional to their momentum, so you can get an image of |ψ[p]|², the momentum-space distribution of the wavefunctions of the individual atoms. So that's cool. But basically you have this tiny little dot of well-arranged well-controlled particles, but you can only do bulk operations on them (including e.g. bulk entanglements by bringing pairs of rows closer together by messing with the lattice and cool stuff like that).

While I'm not clear what the theoretical predictions were, exactly, apparently when they pushed the system into the first temperature regime described above they discovered whatever their theoretical model predicted. Hooray! This has given them some small confidence that maybe their theoretical model is a plausible step forward for understanding high-T superconductivity.

I don't see any error, the image does contain images in the background from the experiments.

By "high-temperature" superconductivity, physicists mean liquid nitrogen temperature, not room temperature. It's progress, but cheap maglev is still a ways off.

>By "high-temperature" superconductivity, physicists mean liquid nitrogen temperature

...sure, but there are superconductors at a lot warmer temperatures than 77K.

mercury barium calcium copper oxide at 133 K (atmospheric pressure). http://adsabs.harvard.edu/abs/1993Natur.363...56S

Hydrogen Sulfide at 203K, under pressure:

http://physicsworld.com/cws/article/news/2015/aug/21/hydroge...

Liquid nitrogen is much easier and cheaper to work with than liquid helium (probably most US high schools see freeze and break a banana or similar experiments regularly; it costs very little).

IMO it would still be a major real world breakthrough when this is ready for engineering use. But while this research may be a big step to that goal, it does not yet move the problem from science to engineering.

I used to do a lot of cryogenics work during my PhD.

The statistic one of the professors often quoted was that "LN2 is cheaper than milk".

Although LN2 is cheaper and more abundant, it's also 20 times warmer than LHe. That matters a lot for applications.

To get an idea of ability to restrict thermal excitations, LN2 at 77K is only 4x 'colder' than room temperature. But LHe (4.2K) is 18x 'colder' than LN2, or 72x 'colder' than room temperature!

The 4x 'colder' here really threw me. Took me a minute to realize you meant 1/4 the temperature. Strikes me as an odd phrasing, like saying "airplanes fly 23x 'lower' than LEO".

It's odd but correct because temperature has a minimum.

We're just used to Celsius/Fahrenheit temperatures where you can't say that.

There is already a short (1 km long) high voltage, nitrogen cooled superconducting cable in use in Germany:

http://www.extremetech.com/extreme/182278-the-worlds-first-s...

Thanks: http://www.nexans.de/eservice/Germany-de_DE/fileLibrary/Down...

I'd say one of the more exciting possibilities is helium-free NMR & MRI.

The high temperature stuff is still very sensitive to strong changing magnetic fields, so I'm not holding my breath for MRI.

But don't ignore improvements in low temperature superconductors engineering:

https://dspace.mit.edu/openaccess-disseminate/1721.1/91644

...I also believe that GE is working on a MRI using liquid hydrogen as the cryogen.

> I also believe that GE is working on a MRI using liquid hydrogen as the cryogen.

What could possibly go wrong?

"This asphyxiant gas is expensive and dangerous if it leaks. What should we do?"

"Well... we could replace the asphyxiant with an explosive gas?"

"..."

Not much. Liquid hydrogen could leak a little. Then it could burn a little. In the liquid form its 100's of degrees away from burning.

It's pretty easy to make high-temperature (liquid nitrogen) super conductors already , I remember making this in undergraduate labs a few years ago:

https://en.wikipedia.org/wiki/High-temperature_superconducti...

The problem with them is that they are not ductile, and only super-conduct in 2 dimensions (along the planes of the material) and therefore it is difficult to do anything with them.

Isn't China building affordable low-speed maglevs? I believe the S1 Line in Beijing is almost finished.

https://en.wikipedia.org/wiki/Line_S1,_BCR

It travels at around 110kph (68mph).

A new low-speed maglev started operation in Changsha last May.[1] This is China's first maglev built with Chinese technology. The Shanghai airport maglev uses the German Transrapid system.

Few countries can build a maglev. A US company tried and failed to build even a simple, slow maglev.[2]

[1] http://www.scmp.com/news/china/society/article/1941693/china... [2] http://ireport.cnn.com/docs/DOC-586439

That seems a bit odd. What's the advantage over an ordinary wheeled train at speeds < 600 km/h?

Well, I imagine that maglev is faster, quieter, and has better acceleration than a subway or light rail. You don't need to go 600 km/h across town.

Getting tens of thousands of people to their destinations 10 minutes quicker adds up.

Wheeled electric trains are already limited in their acceleration rates by passenger comfort, so we don't need superior acceleration or braking. Sound level is the only one advantage that really seems plausible.

Speed?

http://www.nyctransitforums.com/forums/topic/17313-subway-sy...

And for some reason, NYC subways aren't a very smooth ride. Are you sure maglevs wouldn't accelerate faster?

Also, I'd think a maglev from Manhattan to JFK would be preferable to a subway.

What is closer, high temperature superconductors, or fusion power plants?

Well, according the SMAC tech tree, Superconductors come before Fusion power [1]. Kind of makes sense, if you think about it.

[1] http://civilization.wikia.com/wiki/Superconductor_(SMAC)

You need super conductors for the containment of the plasma, but they don't have to be high temperature super conductors.

It sure helps though, and can hopefully keep costs down.

Are these not closely related? IIRC the plasma containment would be a lot easier if the magnets would work in higher temperatures.

What's nice about high-temperature superconductors is they also happen to be high magnetic field superconductors. Higher magnetic fields let one build smaller devices. The problem is they also need to be structurally strong to sustain the forces that such high fields create.

https://en.wikipedia.org/wiki/ARC_fusion_reactor

Add to the list: quantum computers, strong AI, virtual reality.

Flying cars dude!

Fusion's 20 years away. Just like it's always been since ZETA in the late 50s.

I always thought that was a funding thing. It seems like there are a few small improvements every few years, because, I think people who work on that work pretty hard.

It's that they want to build a multi billion dollar thing "to answer questions". Since there's no immediate payoff, it follows the superconducting supercollider path.

Also, it's nuclear power, so that's another nail in the coffin.

I don't really think it's funding. There has - over the last 50 years - been considerable funding from all industrialized countries. The physics of containing a large volume of plasma and injecting cryogenic fuel and turning the resulting energy into something usable (eg. steam) all next to each other is simply not trivial.

Let's see how Wendelstein 7x or the announced micro-fusion devices turn out in operation - maybe they are finally the breakthrough. I am not holding my breath for ITER, though.

Funding: http://i.imgur.com/sjH5r.jpg

Wendelstein 7X is impressive, but it doesn't have the facilities for actual fusion. The best they can do is "theoretical breakeven", which has already been achieved with tokamaks (JT-60 in Japan).

As for "micro-fusion" devices: if you're thinking of Lockheed, as far as I can tell they're full of shit. It's an approach that was tried 50 years ago and failed.

You seem to imply that failure 50 years ago implies failure 10 years from now, which, with all the advances in supporting technologies, is nonsensical. Do you have any solid evidence that Lockheed is full of shit?

No I don't, which is why it was a qualified statement. They've released very little information about their design, and it's up to them to convince the taxpaying public it's anything more than a mirror machine. How do they keep the plasma from squirting out of the sides? That'd be the real innovation, but they're silent on this point. Almost as if they're not worried about it.

Oh, and now it's 10 years from now? I thought they said it'd be ready in five? Wait, three, because they said that two years ago.

The other reason to keep quiet about confinement is that it's their secret sauce. The 10 year number is a deliberately pessimistic one I pulled out of my hat, not meant to be precise. I'm just saying, it's possible that things have changed enough to make possible in the near future what was impossible/impractical in the past.

> [...] simply not trivial

Well, yeah. It's not clear how hard it is. It seems unlikely a high school kid will get power from their farnsworth fusor in their garage. It's not something you can cobble together in your back yard.

In the absence of corruption, will a billion dollars do it? Will 100 billion? 10 trillion? It's not a question we can answer. The answer may be no at any price. I do think a serious effort would have some pretty cool side effects. Perhaps some advances in material science, higher precision in process control, fast dynamic control of magnetic fields.

That said, at what cost? Infrastructure, health care, the F-35, whatever war we want to have next. Dumping a lot of money into fusion power is probably not the optimal answer. But i don't think it's the flat out wrong answer. We don't know what's behind door number 2, It's probably not infinite free power. But there's probably good stuff there, and worth exploring eventually.

Anyway, it's clearly too risky for private enterprise. It seems like one of those questions that federal funding could answer. Again, the answer might be no, it's to hard to do at a reasonable price. Right now, we just have a bunch of questions. As things are, we're going to have a bunch of questions for quite some time.

It's important to keep in mind that power plants are expensive, fullstop. Even a new coal plant costs several billion dollars, and that's century-old technology. The fact that the first generation of a revolutionary new power plant costs ~10X more than that should not surprise anyone.

we don't need fusion https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reacto...

In contrast to fusion (which is 20 years away and always has been), working Thorium reactors and safe disposal of nuclear wast is 50 years away. Since about 50 years.

I don't see how a better Nuclear plant even touches fusion. Fusion is sort of like the perpetual motion machine, nearly free energy.

because Thorium is pretty much free too, as it's everywhere. and meltdowns just stop the reaction and you can recommission the system easily, or just stop the meltdown before it happens.

It'll always be 20 years away until the petroleum economy gets too expensive.

Or while PV continues to drop precipitously in cost.

This is really important. If you can improve conduction efficiency by a percent or two (let alone lossless) you can put solar panels on the other side of the planet and solve global warming in a pinch by piping power to the dark side. Right now it's about 3% at 100kV iirc which translates to ~40% losses best case which, while almost financially feasible, would also cook the planet in a toaster oven. :P

>would also cook the planet in a toaster oven.

That energy is normally converted to heat anyways so it's not like it's that much hotter. Solar panels are going to absorb more light than vegetation would but either way, it's not a huge difference one way or another.

I think a lot of energy gets either bounced into space (desert) or turned into a weird thing like a protein or complex structure which takes away some of the heat by storing it in chemical bonds. Deserts are where you'd put solar panels and i'd gather that vegetation is pretty efficient with absorbed energy. There's a good chance it'd be net positive for heat.

It's the former; most energy is returned to space. Not that much energy is stored in biological systems on the macro scale -- heat waves cause wildfire, not the reverse. Besides, to keep homeostasis or anything resembling it, energy in needs to roughly equal energy out.

Also vegetation is pretty terrible with absorbed energy efficiency. I mean, for goodness sake's it's green, the color right in the peak of the Sun's spectrum. That means the best wavelengths are all reflected. This is a feature, as it really helps quite a bit with keeping albedo higher, even in dark forests, for the purposes of preventing runaway global warming.

The leafs are green because it improves over all efficiency of photosynthesis across spectrum,

http://m.pcp.oxfordjournals.org/content/50/4/684.full

might be a pretty long wire. Is that going to be cheaper than the solar energy microwaved from space?

Define "microwaved from space". Are you talking about the power production, or the power transmission?

If you're talking about production, it's always going to be stupendously cheaper to install solar panels on the ground.

If you're talking about transmission, just look into why we don't already use microwaves for bulk power transmission. One cable can carry gigawatts and lose a couple percent per thousand kilometers. You could go a third of the way around the planet at 75% efficiency. Microwaves are at 75% efficiency to transmit halfway across a room. They're dangerous at high power, and even then your capacity per dish is not going to be very much. Focusing it at such an enormous distance is not going to be easy, and there are extra losses when it travels through the atmosphere.

Beamed energy is much less efficient right now. Wires are long, but we build long wires today. Maintenance will be a pain, but hey at least we'd have a planet.

EDIT: If you want to see my back of the envelope calculations you can check out the second half of this article I wrote: https://medium.com/@willsilversmith/the-future-requires-unit...

What's the difference between space-based directed energy transmission and building-vaporizing laser space weapons?

"solar level" power density, even ten times solar level power density, is still maybe a factor of a million too low to vaporize buildings.

Note that a 2x solar energy flux beam would still be an interesting tactical or strategic weapon. It wouldn't melt or burn anything directly but you could make winter streets very comfortable for protestors, or make summer streets intolerably hot for protestors. Or you could boil off water quicker than letting the sun do it itself, which is nice after a snow storm and not so nice during a drought.

There are a variety of interesting optical resolution limits such that its physically impossible to accidentally turn a "warms up a couple square miles" mirror into a death ray of doom.

Note that like 50 years ago people were pimping 90+% effective microwave antennas... the ground station work was done decades ago and its cheap. Now how you get a multi-megawatt continuous microwave magnetron in orbit and powered is the hard part.

super interesting thx! I didn't think of larger-area, lower intensity beam as an option. Now it's got me thinking of other ideas like adding a few months of growing season to northern & southern farms, which sounds like a cover story of Popular Science magazine from the 70s :D

Nothing!!!! MUAHAHAHAHAHA!

Nobody would build it

More to the point, it starts to look like a space based death ray, which might make other nations a bit nervous...

TLDR: The main finding is: They built a simulation and super cold 2D experimental setup that verified that the "Hubbard" superconducting model is validated to a high degree (for a certain temperature range), and that electrons start forming pairs that "bunch" with empty spaces in the lattice.

Man, I wish the title didn't suggest that high temperature superconductivity experiments were performed.

I know, total clickbait for engineers and nerds.. A similar one would be like, "Woz has THIS to say about new Star Wars movie..." omg, gotta click that...

"You won't believe what Linus just said"

"11 programs Stallman doesn't want you to install"

Link to the article (paywall) [0].

0. http://science.sciencemag.org/content/353/6305/1257

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