Schrodinger's Cat Closer To Reality?

Shipud writes "A group from the University of Oxford is proposing a scheme to achieve quantum superposition in a large object, according to Nature - not as large as Schrodinger's cat, but about ten-thousandth of a square millimiter, some 10^14 atoms. Quantum superposition is the phenomenon in which a photon passing through a beam splitter to takes two paths at once, inconceivable in the macroscopic world. William Marshall and co-workers suggest to mount a tiny mirror on a springy arm, so that the power of a single photon will be enough to oscillate it. When that photon is superposed, it transfers its superposition to the mirror, which will be quantum superposed: at two places at once. Wave particle duality has already been shown in Buckminster fullerenes, a 60 atom compound. Are we getting closer to quantum computers?"

Comments

Yeah...

[Kiriwas]

Achieving superposition is great, but how long is it maintainable? To get truly useful quantum computers, we need states that can be maintained that way, for longer periods of time (or so at least some proposed versions say). fp?

Re:Yeah...

[drkich]

The researchers propose to calm this stormy background by cooling the apparatus to less than two thousandths of a degree above absolute zero. The mirrors would also be in a very high vacuum so as not to be disturbed by colliding gas molecules.

It does not sound like it will be in a case near you any time soon.
Plus it will be in a high vacuum, not a perfect vacuum. So even though the probability of the mirror hitting any gas molecules is low, how reliable are their results?

Re:Yeah...

[Nickybob]

I don't mean to be a spoil sport, but even if they accomplish superposition, we still have Heisenberg to consider, right?

Re:Yeah...

[isaac]

I don't mean to be a spoil sport, but even if they accomplish superposition, we still have Heisenberg to consider, right?

I'm not sure. Maybe we do, and maybe we don't. We'll probably never know for certain.

Re:Yeah...

[Jerf]

So even though the probability of the mirror hitting any gas molecules is low, how reliable are their results?

All experiments have a reliability less then 100%. Techniques to handle that have been around for a long time.

Rest assured the experiment will be performed many, many more times then just "once". (It seems to me you have that as part of your mental image.) Supercollider experiments are run into the hundreds or thousands of times (not certain, not part of that community, could easily be millions for all I know; corrections welcomed).

Can they...

[drkich]

I would love to be able to stay up really freakin' late and sleep at the same time. Now that would be a break through!

Interesting!

[floydigus]

Quantum superposition is the phenomenon in which a photon passing through a beam splitter to takes two paths at once, inconceivable in the macroscopic world.

Whereas Slashdot is the phenomenon in which a sentence takes two paths at once.

Open the box and see

[Dancin_Santa]

Are we getting closer to quantum computers?

Maybe.

Re:Open the box and see

[KDan]

Why do people posting about cool physics stuff invariably feel the need to pepper it with buzzwords like "quantum computers" and what not? This article is interesting and cool and fun without the buzz-reference...

Daniel

Closer to reality?

[henrygb]

Not until they have done the experiment.

This is a hypothetical experiment at this stage. Until they actually try, they will not know if they can actually detect the effect of "the system [cycling] back and forth between a superposition of photon states (in which case one can detect an interference pattern) and a superposition of mirror positions (for which there is no photon interference pattern)." It is possible that it cannot be detected (either since observing whether or not there is an interference pattern may destroy the cycling process or because the cycling is not happening at all), in which case it becomes a philosphical question rather than a scientific one.

Canonical answer

[jolshefsky]

The question:

Are we getting closer to quantum computers?

The answer:

Yes and no.

Obligatory quote

[ManxStef]

inconceivable in the macroscopic world.

You keep using that word. I do not think it means what you think it means.

heating up counts as a measurement

[QEDog]

The cantilever (vibrating arm) is connected to something (the outside). Even if you cool it down a lot, to prevent thermal effects from the outside, the vibrations of the cantilever will heat up the system, and this counts as an observation. The paper doesn't mention how to correct this.

Re:heating up counts as a measurement

[radtea]

This is a good point, but I'm sure the researchers have considered it. The limiting factor will be inelastic flexion of the cantilever, which can be made small in a number of ways, not least of which is keeping the amplitude of vibration small. Given that they're talking about setting the thing vibrating using the momentum transfer from a single photon, this shouldn't be a huge problem!

But it does bring up an important common misunderstanding that the headline of the article repeats: quantum effects have absolutely nothing to do with size and everything to do with complexity. A photon that passes through both slits of a double-slit apparatus demonstrates quantum effects on a scale of a fraction of a millimeter (the separation distance of the slits) and large multi-path interferometers of one kind or another involve photons that take paths that are tens of centimeters or more apart.

Size doesn't matter. What matters is the number of modes available, because interference between modes destroys our ability to observe quantum effects. Systems of many particles (particularly at higher temperatures) have so many modes available that the coherence time is extremely small, although even then we can under the right circumstances observe things like the Mossbauer Effect in which an entire block of material acts as a single quantum-mechanical entity.

--Tom