Hacker News Reader

Comment by sbierwagen | Hacker News Reader

Pure marketing. "Quantum levitation" is just flux pinning[1] as seen in all "high temperature" superconductors. All you need a chunk of type 2 superconductor, a strong magnet, and some liquid nitrogen. Note the 852 videos on youtube: http://www.google.com/search?q=superconductor+levitation&...

You can shell out 80 bucks and do it yourself: http://sargentwelch.com/superconductivity-suspension-and-lev... (LN2 not provided.)

There doesn't appear to be any novel physics here at all.

1: http://en.wikipedia.org/wiki/Flux_pinning

View on HN

> All you need a chunk of type 2 superconductor, a strong magnet, and some liquid nitrogen.

This isn't entirely accurate. A "chunk of type 2 superconductor" would just show the Meissner Effect, which is different than "flux pinning". The Meissner Effect is how superconductors essentially repel magnetic fields, resulting in levitation; it wouldn't necessarily pin the levitating body in-place such that it could follow some track for example.

Flux pinning occurs when some magnetic fields penetrate the superconductor in discrete "tubes" through the imperfections (along the grains) of the superconductor. In order for flux pinning to happen, you must have an extremely thin superconductor (in the case of the video, it's actually a sapphire crystal wafer with a 1-micron thick coating of superconductor ceramic material).

EDIT: Technically, you could also get flux pinning if you were to supercool the superconductor (i.e. make it a superconductor) while it's in the magnetic field of the magnet.

I played quite a bit with the Meissner and the Flux pinning effect. But I was never able to change a flux pinning "on the fly". You always had to reheat the superconductor to something over the transition temperature and then cool it down again inside a magnetic field (in the desired position). But then, it was quite strongly locked in that position and would snap back to where it was when moved.

So, I'm quite curious on how this works ;) Is it because it's a very thin superconductor in this video?

Just to do (dia)magnetic levitation, you could put together 4 cubes of neodymium magnets, then cleave a very thin sheet of pyrolytic graphite and gently suspend it on top of the cubes.

If it's thin enough, it will float.

This is why I love HN. See something that blows my mind. Read comments. Meh. (When I say "love," you know I mean "hate" right?)

What's he marketing exactly? It's a Tel-Aviv University demo at ASTC.

I think naming the device "Quantum Levitation" is marketing. Why can't the student call it what it is?

Students especially have been known to give things cool names just cuz.

I actually did not click on the movie link initially BECAUSE it has the word "quantum" in its title. To me, that's a bee-ess test, if the link is very popular with the media.

Then I saw some comment threads on various sites and I was like "okay, let's see what's going on here". Heh, cute levitation effect.

I thought first that this is the same old levitation effect, but apparently it's something new. At least the effect seems to be much stronger.

"Much stronger"? You can reposition it with your hand!

It's strong enough to not have the springiness you normally see with levitating superconductors.

Reply on news.ycombinator.com