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Quantum State Created In Largest Object Yet
SpuriousLogic writes "A team of researchers have created a 'quantum state' in an object billions of times larger than ever before. From the article: 'Such states, in which an object is effectively in two places at once, have until now only been accomplished with single particles, atoms and molecules. In this experiment, published in the journal Nature, scientists produced a quantum state in an object billions of times larger than previous tests. The team says the result could have significant implications in quantum computing.'"
That's the problem with vague claims in an article. We don't know if the weight is billions of times bigger or if the diameter is. Therefore we don't know if we have 6x10^9 atoms or 6x10^27 atoms. It doesn't even give an order of magnitude -> epic fail of scientific journalism.
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According to the researchers' website the nano-mechanical resonator is a few micrometers in diameter:
http://www.physics.ucsb.edu/~clelandgroup/research.html
The previous record was a buckyball.
Once they've placed this object in a quantum state, how do they verify that it's "occupying two states at once?"
Interference phenomena. The article is light on detail, but presumably they excite the system into a superposition of (mechanical) normal modes and then observe the motion, or the position of some part of it, at a later time and find that it is in a classically forbidden region.
For example, suppose they excite it into two modes that interfere to produce a node at some point, so there is no motion there, but there would be if there it was in one mode or the other. Then monitoring the motion at that point would allow you to determine if the system was in a superposition of two quantum states rather than one or the other.
With regard to the many-worlds interpretation: it doesn't answer the really important question. Neither does consistent histories or any of the decoherence-based approaches. The really important question is, "Why is there a classical world at all?" That is, these theories purport to show that we can get along just fine without the wavefunction ever undergoing "collapse", so in some sense all possible quantum outcomes of an experiment are permitted. But they never answer (or even ask), "Why is it only via interference phenomena that we are aware of these effects? Why aren't we aware of the other components of the wavefunction all the time? Why is there a classical world at all? Is it a feature of consciousness or the physics that permits beings like us to exist, that we are selected by a basically anthropic process to be able to experience only the narrowest subset of existence? If so, how?"
Apart from that, the article is badly misleading: it seems to suggest that anyone anywhere thinks there is anything interesting about the physical size or number of particles involved the detectability of quantum phenomena. It has been known for decades that this is not the case: the number of available modes is what matters, and any sufficiently cold object can become arbitarily large without exhibiting classical behaviour. Furthermore, phenomena like the Mossbaure Effect told us something similar half a century or so ago. It's probably time for the popular press to stop talking about the quantum equivalent of the luminiferous aether and get with the 21st century.
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