Superconducting and normal electrons are not interchangeable

[StanislavD]

TL;DR Summary

Interesting experimental result: superconducting electrons are not interchangeable with normal electrons in the momentum space for seconds. More intriguing: all modern theories of superconductivity assume that superconducting and normal electrons are indistinguishable (i.e. interchangeable in the momentum space).

An interesting paper in NATURE "A superconductor free of quasiparticles for seconds"
https://www.nature.com/articles/s41567-021-01433-7
showing that superconducting (paired) electrons don't hop into normal 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). If so, then the superconducting and normal electrons are not interchangeable during the measurement.
More intriguing: all modern theories of superconductivity assume that all conduction electrons (superconducting + normal) are interchangeable in one shared momentum space. How to solve this paradox?

 

[Hornbein]

Amazing. I have read that the lifetime of pairs was short. I guess they didn't really know.

 

[StanislavD]

If one single pair-breaking-event occurs once per second, then in a pair population the average life time is longer than one second.