Are superconducting and normal electrons interchangeable in the momentum space?

[StanislavDolgopolov]

An interesting result in Nature "A superconductor free of quasiparticles for seconds" https://www.nature.com/articles/s41567-021-01433-7 . It shows that superconducting (paired) electrons don't hop into normal (unpaired) states for seconds. The measurement device detects single pair-breaking-events for a large pair population, so the average life time of each pair is much longer than a few seconds (up to many hours). Thus, the superconducting and normal electrons are not interchangeable in the momentum space during the measurement. More intriguing: all modern theories of superconductivity assume that all conduction electrons (superconducting + normal) are interchangeable within one shared momentum space, i.e. every electron may be awhile superconducting and awhile normal. So it's unclear are superconducting and normal electrons interchangeable or not?

[Lorentz Jr]

I'm not sure this article addresses that question.

[StanislavDolgopolov]

I also was not sure that the article is about that question. However, the experiment shows that superconducting electrons stay permanently in paired states, so we can assert that a paired electron never was normal (at least during the measurement on the device). This fact has interesting consequences. For example, now we may not put all electrons and states into one Slater determinant; but we must form two Slater determinants (a normal and a superconducting ones). And electrons may not hop from one determinant to another one.