Mechanism behind sudden levitation lifetime drop at high photon flux

Determine the physical mechanism responsible for the abrupt decrease in levitation lifetime of a magnetically levitated superconducting PbSn microsphere when the applied laser photon flux exceeds approximately 2×10^7 photons per second. Specify the processes that cause this lifetime reduction and reconcile them with heat-capacity and absorption-based lifetime estimates to explain the observed discrepancy.

Background

In the experiments, the superconducting PbSn microsphere is levitated at cryogenic temperatures and probed optically. The authors measure how the levitation lifetime depends on laser power and find a regime in which the lifetime follows a simple inverse-power trend, consistent with a finite thermal energy budget.

However, when the incident photon flux exceeds about 2×10^7 photons per second, the observed levitation lifetime drops abruptly. Simple heating models based on absorption and heat capacity predict significantly longer lifetimes than measured, indicating additional mechanisms—such as quasiparticle generation, recombination dynamics, or weak electron-phonon coupling—may play a role. The precise cause of the sudden lifetime reduction remains unresolved and is important for optimizing optical readout without quenching superconductivity.