According to my current knowledge, the Cooper-pairs in a closed superconducting circuit should "feel" a centrifugal force. The (-2) charged pairs are therefore accelerated.
Do the Cooper pairs emit photons? Is there some mechanism that prevents it? Even if you look at the complete wavefunction, still there is an electric charge that accelerates. At different points in the circuit, this acceleration is different. I can't find any reason why they shouldn't, but I'm not sure. I'm not sure either if this case the form of the circuit has the same implications as that of a closed circular circuit (apparently not, according to the comments below).
Has the solution to this question has something to do with the Meissner effect, as in the answer below (though I can't see how)?
Or is the emission that small (because of the small acceleration due to the low temperature) that it effectively has no effect on the current's energy? Just stating that the definition of a superconductor is that it experiences no resistance begs the question.
So, Is there anyone who can help me solve this riddle? Much obliged in advance!