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#1




Help understanding quantum cat states and artificial atoms
So the May 27 issue of Science has this article which claims to demonstrate a "cat state" (an observable real world Schrödinger's cat two states existing at the same time occurance, I think the same thing sometimes also called a "Schrödinger's kitten") "in two separate locations at the same time."
Anyone able to help explain what they actually did? I understand that Hilbert spaces are just largen geometric spaces of which the basic rules of geometric transformation/translation, calculus, etc. all apply. But what is "a superconducting artificial atom"? How does it bridge the two cavities? From the article, this is where I knew I was in need of help to understand this! Quote:

#2




I do not really understand much of what they did. There are two papers inside this link here: one being the full published paper and another seeming to be a supplementary about the mechanics of creating the experiment itself.
http://webcache.googleusercontent.co...&gbv=1&ct=clnk so, i guess at worst, if you really want to know what they did then have wikipedia open in another tab to act as a translator for all the new words and ideas they are using. So sorry, explaining anything about this is beyond me. 
#3




Oh I have the article (and I think the link can get you there without even a paywall problem). Individual words are not the issue so much as how they string together into sentences and concepts ...
The basic claim I get. Schrödinger's kittens are macroscopic states which are coherent from a quantum phase POV and are observably in more than one state at a time ... in this case I guess groups of coherent photons that have two sorts of oscillations at the same time. And somehow now in two locations at once too? By way of an artificial atom? 
#4




I haven't completely read the article, but this is how I read it:
In the Schrodinger's cat gedankenexperiment , you have one box which contains a cat which is in an equal superposition of states of [alive] and [dead]. The experiment in the article "recreates" the state of affairs of having a "largeish" system which is in an equal superposition of two intuitively opposing states, but the twist is the system is spread over two spatially separated boxes rather than a single box. Specifically, in the experiment they have two boxes, A and B, and the number of photons bouncing around in each box is in a near equal superposition of states of [box A contains an even number of photons and box B contains an odd number of photons] and [box A contains an odd number of photons and box B contains an even number of photons]. This is achieved by entangling the states in the boxes which is itself achieved by connecting them via a nanoparticle of semiconducting material (i.e. the artificial atom). Last edited by Asympotically fat; 06112016 at 09:50 PM. 


#5




A 'cat state' typically is a superposition of two coherent states with opposite phases. A coherent state is, in some sense, the most 'classicallike' state of an electromagnetic fieldit moves on a classical trajectory through phase space, for instance. So, such a cat state is a superposition of opposing classical states of affairs; hence the name.
They generalize that concept (as Asympotically fat already explained above) by generating a superposition of two cavities containing two coherent states (cavity A and B containing coherent state 1 and cavity A and B containing coherent state 2). (Just parenthetically, I would like to point out that one can't think of coherent states as containing a definite number of photons; they're instead superpositions of definitephotonnumber states, the socalled Fock states.) An 'artificial atom' is generally something like a twolevel (or more) system: the two possible states of the system mirror an atom being in one energy state or another. In this case, it's implemented via a Josephson junction, which can hold different levels of charge. Basically, the 'artificial atom' is used to couple the radiation fields in the two cavities: depending on the level it's in, different transformations are implemented on the fields via microwave interactions; thus, it's used to build (and perhaps read out) the cat state. 
#6




That sounds fishy to me. If they're considering the evenodd state of the photons in each box to be entangled, that seems to suggest that they're assuming that the total number of photons is conserved. But photon number is not only not conserved, it's not even invariant.
Now, it may be that they've managed to contrive some way to keep the evenoddness of the total photon number conserved, but that would take a lot of contriving. 
#7




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#8




Thank you HMHW. That along with the cartoon schematic in the article got me to as much understanding as I at least can reasonably hope for.
Is a "cat state" fundamentally different than what gets called a "Schrödinger's kitten" or a specific sort of instance of one dealing with entangled quasiclassical systems? Am I right in understanding that Hilbert space in this case seems to just be used as the way to express how much is gained in increased potential computing power, in this case the concern for error correction? And hijacking my own op, how difficult is it for traditional computing to manipulate geometric forms in modest n Hilbert spaces? (My longstanding fantasy is related to concepts being represented as ndimensional objects (e.g. the color spindle) and to creative analogy making being the discovery of an unexpectedly good fit of of one geometric object when transformed and applied to another domain. If concepts can be expressed geometrically then a computer that can transform objects in modestly large ndimensional spaces would be engaging in creative analogy making, something that is a hallmark of human creativity.) Thanks. 
#9




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Sometimes, one also hears states that are superpositions of 'contradictory' properties called 'cat states' or similarsuch as, for instance, a superposition of 'all spins up' and 'all spins down'. Quote:
The nice feature of Hilbert space is that there is a way of multiplying two points (vectors) A and B (scalar multiplication) such that the square of the result is the probability of finding state A if the system is in state B. I'm not sure what you're aiming at in terms of computational powerhowever, in a sense, quantum states are very complex objects (the number of parameters needed to describe an nparticle system is exponential in n, while in classical mechanics, each 'particle' only adds 6 coordinatesthree for position, and three for momentum). Quote:
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#10




Thank you for the link. An interesting read but my thoughts had been more inspired by this book and tying it to creativity as an unexpected good fit of analogy making leading to novel ideas.
The bit about computational power comes from my limited understanding of this in the article: Quote:

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