> Well, it may be room temperature superconductivity, but if it isn't also
> "room pressure" superconductivity, then it is still no more useful than > low temp SC.
Not true. If you could get to RTSC with a diamond-anvil
pressure cell, you could put a SQUID magnetometer in there
that would be useful for lots of stuff. Maybe even a
Josephson junction CPU chip that would run Vista XP Pro
at a reasonable speed. What killed IBM's Josephson junction
project was the crazy way materials would break down when
cycled repeatedly to cryogenic temperatures.
I agree that a room-temperature SQUID would be a very useful device,
even though it wouldn't be nearly as good as a low-temperature SQUID.
Hypres used to make a 100-GHz sampling scope based on SQUIDs, but it
needed liquid helium. Pretty amazing device for its time, though.
RE the IBM Josephson project:
They stayed with Pb junctions for too long, and those had the
temperature cycling problem in spades, just as you say. They eventually
went to niobium edge junctions, which survived very well, but by then it
was clear that the speed advantage wasn't enough to justify the
requirement for cryogenic temperatures. (I wasn't on the project, I'm
about 10 years too young, but I know a bunch of the people who worked on
it.)
Cheers,
Phil Hobbs
IBM T. J. Watson Research Center
Yorktown Heights NY
Mark Thorson wrote in
news: snipped-for-privacy@sonic.net:
Bzzzzt, wrong answer! You don't honestly think that they won't break
down equally unpleasantly when cycled repeatedly to diamond anvil
pressures, do you?
A liquid nitrogen refrigerator is an infinitely cheaper, and much
larger, place to build complex widgets, than a diamond anvil. What we
really need to bridge the gap between liquid nitrogen temp
superconductors and room temp superconductors is a dry ice temperature
superconductor (-60F, IIRC), because dry ice refrigerators are even
cheaper than liquid nitrogen refrigerators. ?:D
IMO, what makes Josephson Junction computers uninteresting is that
they're not a better mousetrap, just a different mousetrap.
Larger, sure, but all we're talking about putting in it is a SQUID. You
can make those lithographically on one half of the anvil, and then
assemble it with a big preload, using some sort of
temperature-compensated mount. It ought never to have to be
disassembled, so in principle there's no cycling involved. (That of
course assumes that the metal seal on the cell didn't ever leak.)
The key thing about cryogenics is that they need constantly power and
continual babysitting.
Cheers,
Phil Hobbs
Phil Hobbs wrote in
news: snipped-for-privacy@corp.supernews.com:
I knew you were going to say this, and now we've descended to the nadir
of bickering about what's complex and what isn't. According to my
definition, anything under the purview of "professional science" is by
definition complex. Other categories, like industrial, commercial,
hobbyist and amateur science are by definition easier.
Both steps you described above are intricate and difficult to implement,
and I shudder to think about the complexity of any steps you've left
out. I'm not saying that it can't be done, but just that it's not
*obviously* competitive with other ideas, for research dollars. Other
ideas can provide any or all of the following benefits - quicker
payoff, more important area of research, less effort, cheaper equipment.
Sure, but the same was true of the IBM experiment. Theoretically, once
you've got your widget working, it's reasonable to require that the user
never allow it to return to ambient temp & pressure. In practice, this
is yet another headache for the user, and it only takes a couple like
that to make them throw up their hands and say "It just ain't worth the
hassle." ;(
I'm sure that the anvil requires no less power or babysitting than the
cryo, and cryo setups are much more familiar to lab people than the
anvil. Familiarity = low cost + ease of use.
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