Dadface
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f95toli said:this is not really ambiguous. That the persistent current in the loop correspond to a certain flux follows from "classical" SQUID physics (flux quantization). you can find more about this in any standard textbook on superconductivity (say Tinkham's book).
The 3 junction SQUID used as a qubit is not in any way fundamentally different from a normal 2 junction SQUID. If you calculate the potential energy of the system you will find that the addition of an "extra" small junction gives rise to a double well potential, with the two wells corresponding to clockwise and counter-clockwise persistent currents flowing in the loop, respectively. If you then plug this potential energy into the Schrodinger equation you get what is more or less a complete description of the system (minus the effect of decoherence), anyone who has done say a first course in QM at university can do this.
I am going to be lazy and just refer to the following paper on the arXiv where you can find a brief summary and some references, just ignore the bit about the resonator. I am sure there are better references, but I can't think of one now.
http://arxiv.org/abs/0704.0727
Thank you for the reply but I would be grateful if you could clarify something.I'm fine with the correspondence between flux and current and with the superposition of two flux states. The ambiguity I referred to was that the sentence referred to earlier can be interpreted as the currents being in superposition as well as the flux states.
All I am trying to find out is whether there are any theoretical physicists who work in QM and who believe that there can be events such as an electron flowing in two opposite directions at the same time, or a bar which is vibrating at the same time when it is not vibrating,or a cat which is simultaneously dead and alive,and so on.I don't need details.Thank you.