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Quantum superposition, big enough to see!

In today's Nature online, there's a report of an experimental group who have put a naked-eye visible oscillator (an aluminum-nitride paddle about 30 microns wide) into a quantum superposition of moving and not moving simultaneously.  They cooled the paddle to a few tens of millikelvins, and connected it to a superconducting circuit that could drive the paddle to osciilate. 

After confirming that the paddle was in its quantum ground state (no vibrational energy), they put the superconducting circuit into a superposition of on- and off states, and directly measured that the paddle was in the corresponding superposition of vibrating and not vibrating.

In the words of J.B.S. Haldane, "Life is not only queerer than we imagine, it is queerer than we can imagine."

Update #1:  Science News also has a report on this result, with some slightly different details.  The paper itself is a pay-per-view Nature article.

Update #2:  Science magazine now also has a report on this result, with a better and more detailed explanation of the superconducting phase circuit.


Picture of Quantum superposition, big enough to see!
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rachel7 years ago
Agree with lemonie, this is tantalizing.  How did they "put the quantum circuit into a superposition of 'push' and 'don't push'"?  This may be too hard to explain to the lay person, I admit.  But if it's really "an object large enough to be visible to the naked eye" WHY ISN'T THERE A PICTURE OF IT IN THE QUANTUM STATE???
kelseymh (author)  rachel7 years ago
Hi again, Rachel.  Adrian Cho at Science Magazine has written the best news summary so far on this result.  He has a very nice paragraph explaining the superconducting phase circuit they used:
Cleland and Martinis rely not on a SET, but on a widget called a "phase qubit," a strip of superconductor with a non-superconducting patch in it that acts a bit like a sandbar in a stream of free-flowing electrons.

The details aside, the phase qubit is itself a highly controllable quantum-mechanical system with a ground state and one higher-energy state. Researchers can ease the qubit from one state to the other—or even put it into both states at once—by applying microwaves of a specific frequency.

Without going into engineering details, that's probably the best description you'll get.
rachel kelseymh7 years ago
Awesome, thanks!  That is indeed the article I was hoping to read.
kelseymh (author)  rachel7 years ago
To answer your VERY LOUD QUESTION ;->

The picture you see there is an electron micrograph of the etched chip, showing the oscillator (paddle) structure.  When the whole apparatus is assembled, that chip is part of a structure, all of which is immersed in a liquid helium cryostat (to get to 4 K) which surrounds a dilution refrigerator (to get to millikelvins).  Those things are stainless steel tanks; kind of hard to see through :-/
rachel kelseymh7 years ago
OK fine the actual (non-superposed) vibration is probably not visible to the naked eye anyway, even if there were a camera inside the tank (there are obviously some kind of sensors in there to detect the Wigner density or whatever they did measure).  But maybe super super slo-mo?  I don't know enough about cameras to know if there are any that can detect changes in the megahertz range.  I'd be happy even to look at a tiny blur, though :)

I may just have to buy a subscription to Nature.  All the articles there look fascinating, if utterly obscure to my under-educated self.
kelseymh (author)  rachel7 years ago
It's not hard to explain in principle, but I don't want to explain the wrong thing.  The actual research article is behind a pay-per-view barrier on the Nature website, and there's no preprint out on arXiv :-( 

If you look up Wikipedia articles on "quantum bits" or "qubits", you should find some general information on how experimenters generate superposition states.
Rotten1947 years ago
I'm a bit confused. I'm guessing the object that they manipulated into the quantum superposition is the aluminum-nitride paddle, which is the slightly bent rectangle in the picture? But when watching it, would you see it moving, or not moving? After reading the Science News article, it almost sounds like they dont know, especially this sentence: "If the researchers could make a resonator with longer-lasting vibrations, scientists might be able to test superposition on the macroscopic scale."
kelseymh (author)  Rotten1947 years ago
Yes, the picture shows the resonator, which is 30 microns wide (big enough to see).  That sentence in the SN article does seem to contradict Nature's own news report, which suggests that they did observe the paddle in a superposition state (presumably by doing weak measurements to map out the Wigner density, but I'm just guessing).

I have no idea what the paddle would "look like" in a superposition.  It's natural frequency is in the megahertz range, so I'm not sure you'd actually "see" anything moving; think about a POV display.  
Thanks. Of course, now : "megahertz range, so I'm not sure you'd actually "see" anything moving; think about a POV display. " Doesn't that mean that it is actually moving? Or am I just not understanding it?
kelseymh (author)  Rotten1947 years ago
Well, I was interpreting your and Rachel's questions as, "If I were looking at this thing myself, what would I see?"  My point is that I am not sure whether the superposition state would actually have any naked-eye visible difference from either the ground or the vibrational state.  That conclusion is based on the frequency, which is too fast for the eye to resolve.

If you're asking how the experimenters deduced that (a) they could distinguish the ground from the vibrational state, and (b) that they had put the paddle into a superposition of those two states, then you'd need to read the article.
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